Term Index (S)
Astrophysical terms and names of things beginning with the letter S.
S0
S2
S3
S5
S8
SA
SB
SC
SD
SE
SF
SG
SH
SI
SK
SL
SM
SN
SO
SP
SQ
SR
SS
ST
SU
SV
SW
SX
SY
SZ
- S (Poynting vector): measures directional energy flux density
- S (S-type star): type of star with lines indicating zirconium
- S (entropy): relative measure of the amount of usable energy available
- S (sensitivity function): function of wavelength giving the sensitivity of an instrument
- S (siemens): SI unit of electrical conductance
- S (source function): measure indicating the effect of a material on EMR passing through
- S (spectral flux density): flux or power of radiation per unit area per unit wavelength
- S (sulfur): metal, S, atomic number 16
- S: see Sharpless Catalog
- S: see double star designation
- S Cluster (S-Star Cluster): stellar cluster at the center of the Milky Way
- S Doradus variable (luminous blue variable): type of extremely bright variable stars
- S Doradus variable: see variable star
- S orbital: see electron orbital
- S star: see S-Star Cluster
- Sérsic index: see Sérsic profile
- Sérsic law (Sérsic profile): model of the relative surface brightness across a galaxy
- Sérsic model (Sérsic profile): model of the relative surface brightness across a galaxy
- Sérsic profile: model of the relative surface brightness across a galaxy
- S&T (Sky & Telescope): amateur astronomy publication
- S-class: see S-type star
- S-index (chromospheric activity index): measure of magnetic activity of a star's chromosphere
- s-process: synthesis of elements through neutron capture and beta decay
- neutron capture: combination of an atomic nucleus and a neutron
- r-process: synthesis of elements through neutron capture faster than beta decay
- S-Star Cluster: stellar cluster at the center of the Milky Way
- S-type star: type of star with lines indicating zirconium
- S/m: see siemens
- S/N (signal-to-noise ratio): ratio of the power of a signal to the power of the background noise
- S0 (lenticular galaxy): disk galaxy that has no spirals
- S0 galaxy (lenticular galaxy): disk galaxy that has no spirals
- S2: see S-Star Cluster
- S3MC: see Spitzer Space Telescope
- S5 (Southern Stellar Stream Spectroscopic Survey): spectroscopic survey of seven southern-hemisphere stellar streams
- S5: see Strong Source Surveys
- S8: see sigma-8 tension
- S8 tension (sigma-8 tension): Lambda CDM anomaly regarding matter fluctuation
- S82 (Stripe 82): SDSS field in southern hemisphere
- S1: see Stokes parameters
- S2: see Stokes parameters
- S3: see Stokes parameters
- S4: see Stokes parameters
- S8 tension (sigma-8 tension): Lambda CDM anomaly regarding matter fluctuation
- SN: see globular cluster
- S5 (Southern Stellar Stream Spectroscopic Survey): spectroscopic survey of seven southern-hemisphere stellar streams
- SA: see AGILE
- SA: see IRAS
- SA: see rare designator prefixes
- Sa: see rare designator prefixes
- SAA: see Van Allen belts
- SAAO (South African Astronomical Observatory): South African observatory with SALT telescope
- SAB: see galaxy classification
- SABER: see TIMED
- SABOCA: see Atacama Pathfinder Experiment
- SABRE: see DAMA/LIBRA
- SAC (Shapley-Ames Catalog): 1932 catalog of contemporary data on 1249 galaxies
- Sachs-Wolfe effect: gravitational redshift of the CMB
- Sacramento Peak
- SACS: see rare designator prefixes
- sad trombone: see fast radio burst
- SAF (Société astronomique de France): French non-profit astronomical society
- SAFARI: see SPICA
- Sag A*: SMBH at the center of Milky Way
- Fermi bubbles: gamma-ray features associated with Milky Way center
- Sag DEG (Sagittarius Dwarf Elliptical Galaxy): satellite galaxy of the Milky Way
- SagDIG (Sagittarius Dwarf Irregular Galaxy): most distant galaxy in the Local Group
- SAGE: survey of gas and dust in the Magellanic Clouds
- SAGE-LMC: see SAGE
- SAGE-SMC: see SAGE
- SAGE-Spec: see SAGE
- Sagittarius A* (Sag A*): SMBH at the center of Milky Way
- Sagittarius A*: see galactic center
- Sagittarius A* Cluster (S-Star Cluster): stellar cluster at the center of the Milky Way
- Sagittarius B2 (Sgr B2): GMC near the galactic center
- Sagittarius Dwarf Elliptical Galaxy: satellite galaxy of the Milky Way
- Sagittarius Dwarf Irregular Galaxy: most distant galaxy in the Local Group
- Sagittarius Dwarf Spheroidal Galaxy (Sagittarius Dwarf Elliptical Galaxy): satellite galaxy of the Milky Way
- Sagittarius Stream: see Sagittarius Dwarf Elliptical Galaxy
- Sagittarius Window Eclipsing Extrasolar Planet Search: transit search using HST time
- Sagittarius-Carina Arm: see spiral arm
- Sagnac effect: an effect of the movement of light beams regarding their interference
- Saha equation: equation relating ionization to temperature
- Saha ionization equation (Saha equation): equation relating ionization to temperature
- Saha-Langmuir equation (Saha equation): equation relating ionization to temperature
- SAINT-EX: see SPECULOOS
- Saiph
- Orion: well-known constellation in the northern hemisphere
- SALE: see iSALE
- Salpeter function: see initial mass function
- Salpeter IMF: see initial mass function
- Salpeter time (Salpeter timescale): timescale for black hole growth
- Salpeter timescale: timescale for black hole growth
- SALT (Southern African Large Telescope): 10-meter telescope in South Africa
- SALTICAM: see Southern African Large Telescope
- SAM (semi-analytic model): cosmological model combining analytic and other methods
- SAM: see Mars Science Laboratory
- SAM: see SOAR Telescope
- SAM QC: see Mars Science Laboratory
- SAM-FP: see SOAR Telescope
- SAM-QMS: see Mars Science Laboratory
- SAM-TLS: see Mars Science Laboratory
- SAMI: see Anglo-Australian Telescope
- Sample Acquisition System: see CAESAR
- sampling bias: see selection bias
- sampling error: see selection bias
- Samuel Oschin Telescope (Palomar 48 Inch Telescope): 48 inch Schmidt telescope at Palomar Observatory
- SAN: see rare designator prefixes
- SAND: see rare designator prefixes
- SANE
- sanity check: see back-of-the-envelope calculation
- Santa Barbara Instrument Group: old name of Santa Barbara Scientific, telescope instrument manufacturer
- Santa Cruz
- SAO: see Center for Astrophysics
- SAO: see SAO Star Catalog
- SAO Star Catalog: 1960s catalog
- SAO/ASIAA
- SAO/NASA Astrophysics Data System (Astrophysics Data System): online astrophysics bibliography and paper archive
- SAPTA: see MeerKAT Pulsar Timing Array
- SAR (synthetic aperture radar): method of using moving radar with a stationary target
- SARA (Society of Amateur Radio Astronomers): US organization
- SARAS: survey aiming at highly-redshifted 21-cm detection
- SARAS 1: see SARAS
- SARAS 2: see SARAS
- SARAS 3: see SARAS
- Sardinia Radio Telescope: Italian large single-dish radio telescope
- SARG: see Telescopio Nazionale Galileo
- SAS (XMM-Newton Science Analysis System): software designed to analyze XMM-Newton X-ray data
- SAS: see CAESAR
- SAS 1 (Uhuru): 1970 X-ray space telescope
- SAS 2 (Small Astronomy Satellite 2): 1970s NASA gamma ray space telescope
- SAS 3 (Small Astronomy Satellite 3): 1970s NASA X-ray space telescope
- SAS-A (Uhuru): 1970 X-ray space telescope
- SAS-B (Small Astronomy Satellite 2): 1970s NASA gamma ray space telescope
- SAS-C (Small Astronomy Satellite 3): 1970s NASA X-ray space telescope
- SAS-D (International Ultraviolet Explorer): 1980s ultraviolet space telescope
- Saskatoon: 1990s survey to measure CMB anisotropy
- SASS: see CubIXSS
- SASSy: see SCUBA
- SaSt: see rare designator prefixes
- SAT: see Simons Observatory
- SAT: see aperture synthesis
- satcon (satellite constellation): group of many coordinated satellites such as for communication
- Satech-01: Chinese experimental spacecraft
- satellite: see moon
- satellite constellation: group of many coordinated satellites such as for communication
- satellite constellation: type of communication system incorporating tens/hundreds of satellites
- satellite galaxies
- satellite galaxy: galaxy that orbits a larger galaxy
- satellite mega-constellation (satellite constellation): group of many coordinated satellites such as for communication
- satellite plane problem: satellite galaxies inexplicably tend to fall in a plane
- saturated Hanle effect: see Hanle effect
- saturation: see humidity
- Saturn: second largest planet in the solar system
- Cassini: explorer spacecraft sent to Saturn
- Dragonfly: Titan flying rover under development
- Enceladus: Saturn moon considered possible carrier of life
- Enceladus Life Finder: mission to search for life on Saturn moon Enceladus
- Enceladus Orbilander: concept for a NASA mission to Enceladus
- giant planet: planet of more than 10 Earth masses
- grand tack hypothesis: solar system formation model with Jupiter and Saturn migrating
- gravity sounding: measuring a planet's gravitation field by study of nearby probe flights
- helium rain: possible source of heat in giant planet atmospheres
- ring system: disk or set of rings orbiting a planet
- shepherd moon: small moon affecting outer edge of a planet's ring
- solar system object: the Sun, solar system planets, minor planets, comets, and moons
- TAM: non-gray-RT 3D model of Titan's atmosphere
- Titan: well-known Saturn moon
- Voyager: space probes to observe planets and the edge of the solar system
- Saturn II (Enceladus): Saturn moon considered possible carrier of life
- Saturn V
- Saturn VI (Titan): well-known Saturn moon
- Saurer: see rare designator prefixes
- SAURON: see William Herschel Telescope
- SAVAL (Sociedad Astronómica de Valparaíso y Viña del Mar): Chilean amateur astronomy society
- SaWe: see rare designator prefixes
- SAX: see BeppoSAX
- SAXO: see European Southern Observatory Very Large Telescope
- SAXO: see SPHERE
- SB (spectroscopic binary): binary star detected by movement indicated by Doppler shifts in the spectrum
- SB (surface brightness): brightness per unit area of a surface
- SB: see rare designator prefixes
- SB1: see double-line spectroscopic binary
- SB1: see spectroscopic binary
- SB2 (double-line spectroscopic binary): spectroscopic binary star where a specific line shows up at two different wavelengths
- SBB: see Big Bang
- SBF (surface brightness fluctuation): apparent indication of an elliptical galaxy's distance
- SBH: see supermassive black hole
- SBIG (Santa Barbara Instrument Group): old name of Santa Barbara Scientific, telescope instrument manufacturer
- SBIG STX-6303: see Las Cumbres Observatory
- SBNC (Small Bodies Names Committee): old name of IAU Committee for Small Body Nomenclature
- SBS (Second Byurakan Survey): 1970s-1990s survey of galaxies and quasars
- SBS 0335-052: blue compact galaxy
- SC (stellar cluster): group of stars apparently formed by a single cloud
- SC: see rare designator prefixes
- scalar boson
- scalar curvature: see curvature
- scalar field: see mathematical field
- scalar field dark matter (fuzzy dark matter): concept of extremely light dark matter particles
- scalar spectral index: see Lambda-CDM model
- scalar-tensor gravity: GR-like gravity that incorporates a scalar field
- scalar-tensor-vector gravity: see scalar-tensor gravity
- scale
- scale factor: relative size of the universe as a function of time
- scale height: measure of exponential falloff
- scale length: see scale height
- scaling relation: see standard candle
- scan pattern: see intensity mapping
- scan speed: the speed at which the telescope changes angle on the sky while observing
- scandium
- Am star: A-type star with metallic lines
- SCAP: 1980s balloon-borne ultraviolet telescope
- SCAP-1909: see SCAP
- SCAP-2000: see SCAP
- SCARLET: see atmospheric model
- scatter broadening: see fast radio burst
- scatter plot: plot of points within two dimensions
- scatter plot matrix: see scatter plot
- scattered disk
- scattered disk object
- scattered disk objects
- scattered Kuiper belt object
- scattered light: see stray light
- scattering: changing the direction of a particle's movement
- emission: addition of photons to a beam of EMR
- scattering angle: see cross section
- scattering coefficient: see absorption coefficient
- SCE: see Ulysses
- SCExAO: see Subaru Telescope
- SCF (supercritical fluid): state of matter at sufficient pressure and temperature
- Schönberg-Chandrasekhar limit: maximum stellar isothermal helium core mass
- Schechter function: see luminosity function
- Schechter luminosity function: see luminosity function
- Schiaparelli: see ExoMars
- Schiaparelli: see Trace Gas Orbiter
- Schiefspiegler: type of off-axis reflector telescope
- Schmidt camera: telescope type with a very wide field of view
- Schmidt corrector plate: see Schmidt camera
- Schmidt law (Kennicutt-Schmidt law): relation between gas density and star formation rate
- Schmidt telescope (Schmidt camera): telescope type with a very wide field of view
- Schmidt-Cassegrain telescope: see Schmidt camera
- Schmidt-Newton telescope: type of reflector telescope
- Schmidt-Newtonian telescope (Schmidt-Newton telescope): type of reflector telescope
- Schoenberg: see rare designator prefixes
- Scholz's Star: nearby binary star with red dwarf and brown dwarf
- Schrödinger equation: quantum-mechanical wave-equation-like equation
- Schrödinger-Newton equation (Schrödinger-Poisson equation): Schrödinger equation including a term for gravity
- Schrödinger-Poisson equation: Schrödinger equation including a term for gravity
- Schroedinger equation
- Schuster-Schwarzschild approximation (Schuster-Schwarzschild model): simplified model of a star's production of absorption lines
- Schuster-Schwarzschild model: simplified model of a star's production of absorption lines
- Schwarzschild black hole: see black hole model
- Schwarzschild density: see Schwarzschild radius
- Schwarzschild diameter: see Schwarzschild radius
- Schwarzschild lens: see gravitational lensing
- Schwarzschild metric: see metric
- Schwarzschild object: see black hole model
- Schwarzschild radius: radius of a black hole's event horizon
- black hole shadow: dark-disk appearance of a black hole viewed from a distance
- event horizon: surface-shape around a black hole through which light cannot escape
- Schwarzschild telescope: type of two-mirror reflector telescope
- Schwarzschild throat: see wormhole
- Schwarzschild wormhole: see wormhole
- Schwarzschild-Couder Telescope
- Schwarzschild-Couder telescope
- SCI: see Hayabusa2
- science
- abundances: relative amounts of each chemical element
- asteroseismology: study of stars through analysis of their pulsation
- astrobiology: study of extra-terrestrial life
- astrometry: precise measurement of the position and movement of stars
- astronomy: study of astronomical objects and their environments
- astrophysics: physics applied to astronomy
- basal: from the base or from below
- basalt: an igneous rock type that shows rapid cooling
- bathymetry: study and measurement of sea depths
- blind analysis: performing experimental analysis without knowing the data
- cosmology: study of the life of the universe
- cryogenic spectroscopy: laboratory spectroscopy of materials cooled to cryogenic temperatures
- decadal survey: type of once-a-decade planning report from NASA and the NAS
- European Research Infrastructure Consortium: science and technology initiative
- extragalactic astronomy: astronomy of other galaxies, galaxy clusters, AGNs, quasars, etc.
- fiducial: taken as a standard
- forward model: model producing potential observable values from parameters
- galactic astronomy: astronomy confined to the Milky Way
- geochemistry: the chemistry of the Earth, planets, and moons
- Goddard gravity model: gravity model produced by Goddard Space Flight Center
- gravimetry: measurement of gravity's strength
- hydrology: study of the movement of water
- in situ: on site
- interferometry: analysis of superimposed EMR waves
- interstellar astrophysics: astronomy of the ISM including dust and clouds
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- low frequency radio astronomy: astronomy using the lower end of the radio spectrum
- millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
- optics: science and technology regarding visible light
- photochemistry: study of the chemical effects of light
- photometry: studying starlight using optical filters
- planetary protection: the principle of avoiding the contamination of planets with Earth life forms
- planetary science: study of planet characteristics
- plasma astrophysics: includes cosmology, IGM, ISM, HI regions
- polarimetry: measurement of polarization of EMR
- principal investigator: lead researcher in a scientific endeavor
- Python: programming language used for a lot of astrophysics research
- radio astronomy: astronomy observation and analysis of radio EMR
- radio science: radar and other methods of using radio to probe planets and moons
- relativistic astrophysics: physics applicable to cosmology and strong field gravity
- RMS astronomy: collective term for radio, millimeter, and submillimeter
- scale height: measure of exponential falloff
- search for extraterrestrial intelligence: search for radio signals sent from extraterrestrial sources
- selection bias: selection of a sample set that is not appropriately randomized
- sigma: indication of the confidence level of an experiment
- SIMSTACK: software to correlate intensity maps with sources
- solar physics: study of the physics of the Sun
- spectrography: charting the strengths of different electromagnetic wavelengths
- spectrometry: measuring the strengths of different electromagnetic wavelengths
- spectroscopy: measurement of light with various electromagnetic wavelengths
- stellar astronomy: astronomy of the birth, structure, variety, evolution, and fate of stars
- stratigraphy: study of rock layering
- submillimeter astronomy: astronomy observation and analysis of borderline infrared EMR
- synoptic: general, covering everything
- synthetic photometry: deriving photometry-style data from spectroscopy
- thermodynamics: physics of heat and energy
- time-domain astronomy: observing and analyzing changes in astronomical objects
- tomography: observation of sections of a 3D object
- tortuosity: describes something curved with many twists and turns
- transient astronomy: study of short-term astronomical phenomena
- ultraviolet astronomy: astronomy observation and analysis of UV
- Science and Engineering Research Council: old name of UK's EPSRC
- Science and Technology Facilities Council, UK: UK research agency
- Science Instrument Module: see Chandra X-ray Observatory
- Science Run: see LIGO
- scientific notation
- dex: a number or ratio's log base 10
- scintillation (twinkling): blinking, apparent movement and color changes of observed stars
- scintillation: see scintillator
- scintillation: see scintillometry
- scintillator: instrument part designed to respond to high-energy photons
- scintillometer: see scintillometry
- scintillometry: measuring of twinkling
- SCIP: see STEREO
- SciPy: Python library for scientific programming
- SCJ: see double star designation
- SCl: see supercluster
- SCl 117 (Coma Supercluster): nearby supercluster
- SCl 128 (Hydra-Centaurus Supercluster): near neighbor of Local Supercluster
- SCl 40 (Perseus-Pisces Supercluster): nearby supercluster
- SCM: see Magnetospheric Multiscale Mission
- SCM: see rare designator prefixes
- THEMIS: set of satellites studying the Earth's magnetic field
- Sco OB2 (Scorpius-Centaurus Association): nearby OB association
- Sco-Cen (Scorpius-Centaurus Association): nearby OB association
- SCORPIO: see Large Altazimuth Telescope
- SCORPIO-2: see Large Altazimuth Telescope
- Scorpius-Centaurus Association: nearby OB association
- Scott effect: bias toward finding clusters that have bright galaxies
- SCP (Supernova Cosmology Project): used supernova data to determine a history of the universe's expansion
- SCP: see SUNRISE
- SCR: see SuperCOSMOS Sky Survey
- SCR: see solar energetic particle
- SCT: see Schmidt camera
- SCUBA: submillimeter instrument on James Clark Maxwell Telescope
- SCUBA-1: see SCUBA
- SCUBA-2: see James Clerk Maxwell Telescope
- SCUBA-2: see SCUBA
- AMUSE²: survey of ELANs
- JINGLE: survey of dust and gas in galaxies
- SCUBA-2 All Sky Survey: see SCUBA
- SCUBA-2 Ambitious Sky Survey: see SCUBA
- Sculptor Dwarf
- Sculptor Galaxy (NGC 253): spiral galaxy 11 million light-years away
- Sculptor Void
- Sculptor Wall: large slab of galaxies
- Scutum-Centaurus Arm: one of two spiral galaxy arms from the Milky-Way bar
- Scutum-Centaurus Arm: see spiral arm
- Scutum-Crux Arm (Scutum-Centaurus Arm): one of two spiral galaxy arms from the Milky-Way bar
- SD: see Type Ia supernova problem
- SD: see supernova progenitor
- sd (subdwarf): star less bright than the main sequence given its spectral class
- SD2: see Rosetta
- SDC: see Hale Telescope
- SDF (Subaru Deep Field): survey of a small region of the sky using the Subaru telescope
- SDI: see speckle suppression
- SDIC (Solar Influences Data Analysis Center): Royal Observatory of Belgium division on solar weather data
- SDO (Solar Dynamics Observatory): 2010 satellite observing the Sun
- SDOR: see variable star
- SDOs
- SDP: see Magnetospheric Multiscale Mission
- SDSS (Sloan Digital Sky Survey): imaging survey of 500,000,000 objects in 35% of sky
- SDSS IV
- SDSS J065133.34+284423.4 (WD J0651+2844): binary pair of closely-orbiting white dwarfs
- SDSS photometric system (ugriz photometric system): photometric system used for SDSS
- SDSS Strpie 82 (Stripe 82): SDSS field in southern hemisphere
- SDSS-DR12 Quasars: catalog of quasar information in SDSS DR12
- SDSS-DR12Q (SDSS-DR12 Quasars): catalog of quasar information in SDSS DR12
- SDSS-DR16 Quasars: catalog of quasar information in SDSS DR16
- SDSS-DR16Q (SDSS-DR16 Quasars): catalog of quasar information in SDSS DR16
- SDSS-I: see Sloan Digital Sky Survey
- SDSS-II: see Sloan Digital Sky Survey
- SDSS-III: see Sloan Digital Sky Survey
- APOGEE: SDSS near-infrared survey of stars
- SDSS-IV: see Sloan Digital Sky Survey
- SDSS-V: see Sloan Digital Sky Survey
- SDSSp: see Sloan Digital Sky Survey
- SE: see double star designation
- sea level
- gravitational potential model: mathematical model of an astronomical body's gravitational field
- J2: geopotential coefficient regarding a planet's oblateness
- SEAAN (Southeast Asia Astronomy Network): astronomy research/education organization
- search for extraterrestrial intelligence: search for radio signals sent from extraterrestrial sources
- Search for Habitable Planets Eclipsing Ultra-cool Stars (SPECULOOS): search for Earth-like exoplanets orbiting nearby dim stars
- sec (arcsecond): a 3600th of an angular degree
- SECCHI: see STEREO
- second (arcsecond): a 3600th of an angular degree
- second: see right ascension
- Second Byurakan Survey: 1970s-1990s survey of galaxies and quasars
- second dredge-up: see dredge-up
- second of arc (arcsecond): a 3600th of an angular degree
- second of right ascension: see arcsecond
- second order perturbation problem: see perturbation theory
- Second Palomar Observatory Sky Survey: see Palomar Observatory Sky Survey
- Second Reference Catalogue of Bright Galaxies: see Reference Catalogue of Bright Galaxies
- second-order TOF: see theory of figures
- secondary anisotropies: see CMB anisotropies
- secondary eclipse: eclipse of a body that also transits
- secondary mirror: see primary mirror
- secondary modes: see CMB polarization
- sectorial coefficients
- secular: occurring slowly over a long period of time
- Laplace radius: a radius for a stable orbit of a satellite around a planet
- secular evolution: see secular
- secular GI: see gravitational instability
- secular gravitational instability: see gravitational instability
- secular motion: see secular
- secular parallax: see parallax
- secular resonance: see orbital resonance
- secular variation: see secular
- SED (spectral energy distribution): function or plot of brightness at each wavelength in the spectrum
- SED fitting: see spectral energy distribution
- sedimentation: settling of heavier material to the bottom
- SEDM: see Palomar 60-inch Telescope
- Sedna: distant solar system planetoid discovered in 2003
- sednoid: see trans-Neptune object
- Sedov expansion: see blastwave
- Sedov length: see blastwave
- Sedov-Taylor expansion: see blastwave
- Sedov-Taylor phase: see supernova remnant
- SEDS (Spitzer Extended Deep Survey): survey of galaxy mass and black holes through life of the universe
- SEDS (Students for the Exploration and Development of Space): student-run organization focused on space exploration
- SEDs
- SEE: see TIMED
- SEE: see double star designation
- seeing: apparent blurring and twinkling of objects seen through atmosphere
- seeing limited: see diffraction limited
- seeing limited: see seeing
- seeing number: see seeing
- segmented mirror: a telescope mirror formed of an array of smaller mirrors
- SEGUE: see Sloan Digital Sky Survey
- Segue: see Sloan Digital Sky Survey
- Segue 1
- Segue 2
- Segue 3: faint star cluster i the constellation Pegasus
- SEGUE-2: see Sloan Digital Sky Survey
- SEI: see double star designation
- Seidel aberrations: see aberration
- Seidel errors: see aberration
- SEIS: see InSight
- seismic waves: waves broadcast through Earth from earthquakes
- seismograph: see quake
- seismology: see seismic waves
- seismometer: see quake
- selection bias: selection of a sample set that is not appropriately randomized
- selectron: see supersymmetry
- SELENE: 2007-2008 Japanese lunar probe
- Selenological and Engineering Explorer (SELENE): 2007-2008 Japanese lunar probe
- self-absorption: EMR absorption by the same substance that emitted it
- self-gravitating body: see self-gravitation
- self-gravitation: gravitational force holding a body together
- self-gravity (self-gravitation): gravitational force holding a body together
- self-interacting dark matter: see atomic dark matter
- semi-analytic model: cosmological model combining analytic and other methods
- semi-analytical model
- GALFORM: semi-analytic galaxy formation model
- semi-heavy water: see deuterium
- semi-major axis: maximum radius of an ellipse
- semi-minor axis: see semi-major axis
- semiconductor detector: see particle spectrometer
- semidetached binary: see binary star
- semidetached binary: see contact binary
- semimajor axis
- semiregular variable: see variable star
- sensitivity: see balanced accuracy
- sensitivity function: function of wavelength giving the sensitivity of an instrument
- sensor plane (focal plane): plane within optical system at which an image is in focus
- sensor tilt: see focal plane tilt
- SEP (solar energetic particle): high-energy particles from the Sun
- SEP: see MAVEN
- separation
- SEPIA: see Atacama Pathfinder Experiment
- DeGaS-MC: APEX survey of potential star formation regions in the Magellanic Clouds
- SEPICA: see Advanced Composition Explorer
- SEQUELS: see Baryon Oscillation Spectroscopic Survey
- SEQUOIA: see Large Millimeter Telescope
- SERC (Science and Engineering Research Council): old name of UK's EPSRC
- IRAS: 1983 satellite that surveyed the sky in infrared
- UK Schmidt Survey: photographic survey of the southern hemisphere sky
- series: see series expansion
- series approximation: see series expansion
- series expansion: arithmetic series whose limit is equal to a function
- Serpens Cloud: molecular cloud with SF regions
- Serpens Main: see Serpens Cloud
- Serpens Molecular Cloud (Serpens Cloud): molecular cloud with SF regions
- Serpens South: see Serpens Cloud
- Serrurier truss
- Sersic: see rare designator prefixes
- SERVS (Spitzer Extragalactic Representative Volume Survey): infrared survey of some well-studied fields
- SES: see STELLA
- SESAME: see Rosetta
- SESN: see core collapse supernova
- SEST (Swedish-ESO Submillimetre Telescope): 1990s 15 m submillimeter telescope in Chile
- SEST (Swedish-ESO Submillimetre Telescope): former 15 m radio telescope array in Chile
- Set of Identifications, Measurements and Bibliography for Astronomical Data (SIMBAD): online database of astronomical objects
- SETI (search for extraterrestrial intelligence): search for radio signals sent from extraterrestrial sources
- SETI Institute: see search for extraterrestrial intelligence
- Sextans: see rare designator prefixes
- Sextans Dwarf Spheroidal
- Seyfert
- Seyfert galaxy: visible active galaxy
- SF (star formation): theorized collapse of gas and dust into stars
- SF main sequence (galaxy main sequence): relation between galaxies' star formation and stellar mass
- SF rate (star formation rate): rate at which material such as gas is turned into stars
- SF region (star-forming region): area forming stars and/or ready for star formation
- SFA: see eXTP
- SFE: see star formation rate
- SFG: see galaxy main sequence
- SFG: see starburst galaxy
- SFH (star formation history): star formation rate as a function of time
- SFH Camera: see Fred Young Submillimeter Telescope
- SFM (synthetic field method): method of testing galaxy opacity
- SFO: see rare designator prefixes
- SFR (star formation rate): rate at which material such as gas is turned into stars
- SFR (star-forming region): area forming stars and/or ready for star formation
- SFRD: see star formation rate
- SFRG: see radio galaxy
- SFU: see IRTS
- SGB: see subgiant
- SGB: see supergalactic coordinate system
- SGD: see Hitomi
- SGF (SpaceGuard Foundation): private organization to discover and track NEOs
- SGL: see natural astronomical telescopes
- SGL: see supergalactic coordinate system
- SGR (soft gamma repeater): object that produces repeated gamma-ray bursts
- magnetar: neutron star with a strong magnetic field
- SGR 1935+2154: Milky Way SGR generating FRBs
- Sgr A* (Sag A*): SMBH at the center of Milky Way
- Sgr B2: GMC near the galactic center
- Sgr dE (Sagittarius Dwarf Elliptical Galaxy): satellite galaxy of the Milky Way
- Sgr dSph (Sagittarius Dwarf Elliptical Galaxy): satellite galaxy of the Milky Way
- SGR Dwarf (Sagittarius Dwarf Irregular Galaxy): most distant galaxy in the Local Group
- Sgr I Dwarf (Sagittarius Dwarf Elliptical Galaxy): satellite galaxy of the Milky Way
- SGR J1745-2900: magnetar orbiting the Milky Way SMBH
- SGRB (short gamma-ray burst): GRB lasting less than two seconds
- SGRB: see gamma-ray burst
- SGRS: see rare designator prefixes
- SGW (Sloan Great Wall): large slab of galaxies discovered in SDSS
- Sh: see Herschel Double Star Catalog
- sh (shell star): type of star with broad and narrow absorption lines
- sh 2-276 (Barnard's Loop): emission nebula in Orion
- SH0ES: survey to increase the accuracy of the cosmic distance ladder
- Sh1: see Sharpless Catalog
- Sh2 (Sharpless Catalog): catalog of HII regions found on Palomar plates
- Shack-Hartmann sensor: see wavefront sensor
- Shajn: see rare designator prefixes
- Shakhbazian: see rare designator prefixes
- Shakura-Sunyaev disk (alpha disk): well-known model of an accretion disk
- ShAl: see rare designator prefixes
- shallow atmosphere models: see Juno
- shallow Mars-crosser: see Mars crosser
- SHAM: method of galaxy mock-catalog creation
- Shane Telescope: 3.05 m reflector telescope at Lick Observatory
- Shaped Antenna measurement of the background Radio Spectrum (SARAS): survey aiming at highly-redshifted 21-cm detection
- Shapiro delay: EMR delay due to passing near massive object
- Einstein delay: EMR delay due to relativistic effects of environment and motion
- Shapiro time delay (Shapiro delay): EMR delay due to passing near massive object
- Shapley: see rare designator prefixes
- Shapley-Ames Catalog: 1932 catalog of contemporary data on 1249 galaxies
- Shapley-Ames Catalog of Bright Galaxies (Shapley-Ames Catalog): 1932 catalog of contemporary data on 1249 galaxies
- Shapley-Curtis Debate (Great Debate): historical debate regarding the nature of galaxies
- SHARAD: see Mars Reconnaissance Orbiter
- SHARC: see Caltech Submillimeter Observatory
- SHARC II: see Caltech Submillimeter Observatory
- SHARDS: GTC survey in GOODS-N field for quenched galaxies at z = 1 to 2.3
- SHARK: see Large Binocular Telescope
- SHARK-NIR: see Large Binocular Telescope
- SHARK-VIS: see Large Binocular Telescope
- SHARP: see Caltech Submillimeter Observatory
- Sharpless 103 (Cygnus Loop): supernova remnant in Cygnus
- Sharpless Catalog: catalog of HII regions found on Palomar plates
- SHB: see double star designation
- shearing box: method of simulating 3D MHD in disks
- SHeFI: see Atacama Pathfinder Experiment
- SHELA (Spitzer HETDEX Exploratory Large Area Survey): Spitzer-based survey of galaxies
- shell: hollow shaped region of some kind of ISM
- shell (electron shell): radius-level around an atomic nucleus at which electrons can orbit
- shell (mass shell): conceptual volume of mass shaped like a hollow sphere
- shell flash: see helium flash
- shell galaxy: galaxy with one or more surrounding layers of brightness
- shell star: type of star with broad and narrow absorption lines
- shell-type remnant: see supernova remnant
- shepherd moon: small moon affecting outer edge of a planet's ring
- shepherding moon (shepherd moon): small moon affecting outer edge of a planet's ring
- Sher: see rare designator prefixes
- SHERLOC: see Mars 2020
- SHFI: see Atacama Pathfinder Experiment
- shielding effect: see electron screening
- shift-and-add: common speckle-suppression technique
- speckle imaging: method of combining short-term images to yield better resolution
- SHJ: see Herschel Double Star Catalog
- Shk: see rare designator prefixes
- SHOC: see rare designator prefixes
- shock (shock wave): abrupt propagating disturbance in a fluid
- shock capture scheme
- shock front (shock wave): abrupt propagating disturbance in a fluid
- shock heating: see shock wave
- shock tracer: see shock wave
- shock wave: abrupt propagating disturbance in a fluid
- shooting star: see meteoroid
- short gamma-ray burst: GRB lasting less than two seconds
- short gamma-ray burst: see gamma-ray burst
- short Rossby wave: see Kelvin waves
- short-period comet: see long-period comet
- shot noise (photon noise): variation in light measurement due to its quantum nature
- shot noise level: see photon noise
- showyourwork!: workflow software for reproducible research
- SHS: see SuperCOSMOS Sky Survey
- shudder speed (exposure time): time spent acquiring a signal
- Shuttle Pointed Autonomous Research Tool for Astronomy (SPARTAN): series of astronomy satellites launched/retrieved by Space Shuttles
- SI: standardized metric system
- SI: see sulfur
- CGS: metric system variant
- joule: SI unit of energy
- kelvin: unit of temperature scale starting at absolute zero
- magnetic flux: measure of magnetism passing through a surface
- magnetic flux density: vector field describing magnetism in relation to the Lorentz force
- mole: unit roughly the count of hydrogen atoms in a gram
- siemens: SI unit of electrical conductance
- tesla: unit of magnetic flux density
- watt: SI unit of power
- Si (silicon): metal, Si, atomic number 14
- SID: see solar storm
- side lobe: see beam
- CLEAN: algorithm to extract usable images from interferometry-produced images
- dirty image: image that includes the distortions of the beam and sampling
- sidereal: relative to the fixed position of the stars
- sidereal day: see sidereal
- solar day: length of a solar system planet or Moon's day
- solar time: time based upon the position of the Sun in the Earth's sky
- Venus: second inner-most planet in the solar system
- sidereal month: see sidereal
- sidereal orbital period: see sidereal
- sidereal period: see sidereal
- orbital period: length of time for an orbiting object to complete one cycle
- synodic period: period until a planet returns to the same position relative to the Sun
- sidereal rotation period: see rotation period
- sidereal rotation period: see sidereal
- synodic period: period until a planet returns to the same position relative to the Sun
- sidereal time: see sidereal
- solar time: time based upon the position of the Sun in the Earth's sky
- sidereal year: see sidereal
- siderophile: material that dissolves in molten iron
- siderophile element (siderophile): material that dissolves in molten iron
- Siding Spring Observatory: observatory in New South Wales, Australia
- siemens: SI unit of electrical conductance
- siemens per meter: see siemens
- SiFAP2: see Telescopio Nazionale Galileo
- SIFS: see SOAR Telescope
- SIFUS: see SOAR Telescope
- SIGHT: see Hale Telescope
- sight line (line of sight): line between observer and observed object
- SIGMA: see GRANAT
- sigma: indication of the confidence level of an experiment
- sigma-8: see sigma-8 tension
- sigma-8 tension: Lambda CDM anomaly regarding matter fluctuation
- Sigma-D relation: see Faber-Jackson relation
- signal
- signal-to-noise: see signal-to-noise ratio
- signal-to-noise ratio: ratio of the power of a signal to the power of the background noise
- signature (spectral signature): spectral characteristics indicating the emitting material and conditions
- signatures of formation: qualities of a body that suggest how it was formed
- SII: see intensity interferometer
- SII: see sulfur
- silica
- basalt: an igneous rock type that shows rapid cooling
- geochemistry: the chemistry of the Earth, planets, and moons
- silicate: type of compound including silicon and oxygen
- silicate weathering feedback: feedback mechanism stabilizing carbon in Earth atmosphere
- silicon: metal, Si, atomic number 14
- silicon burning: alpha process fusion starting at silicon
- silicon dioxide
- silicon monoxide: compound of silicon and oxygen, one atom each
- silicon-burning shell: see silicon burning
- Silk damping (diffusion damping): a damping process within the plasma during recombination
- Silver Coin Galaxy (NGC 253): spiral galaxy 11 million light-years away
- Silver Dollar Galaxy (NGC 253): spiral galaxy 11 million light-years away
- SIM (Space Interferometry Mission): past space interferometer plan for parallax and exoplanet detection
- SIM: see Chandra X-ray Observatory
- SIMBA: galaxy formation simulation code
- SIMBA: see Swedish-ESO Submillimetre Telescope
- Simba (SIMBA): galaxy formation simulation code
- SIMBAD: online database of astronomical objects
- Simeis: see rare designator prefixes
- Simons Array: telescope array to map CMB polarization
- Simons Observatory: CMB observatory on Atacama Desert
- SIMP: 2000s infrared proper-motion survey
- SIMPLE: see European Extremely Large Telescope
- simple Bouguer correction: see Bouguer anomaly
- simple Bouguer reduction: see Bouguer anomaly
- simple crater: see complex crater
- simple stellar population (SSP): set of stars born at the same time with the same metallicity
- A-LIST: catalog of templates of H-band spectra for SPS
- simplex
- Simplified Arbitrary Lagrangian Eulerian: see iSALE
- SIMSTACK: software to correlate intensity maps with sources
- simulation
- AREPO: cosmology simulation using moving mesh technique
- ARTEMIS: simulations of Milky-Way-like galaxy halos
- Astrid simulation: cosmological simulation over z = 99 to 3
- AstroBEAR: MHD simulation system
- Bolshoi simulation: cosmological simulation
- Castro: hydrodynamics simulation software
- ChaNGa: cosmological-simulation project active since circa 2015
- Cloudy: code to model the effect of gas and plasma on spectra
- CMFGEN: RT code designed to handle significant stellar wind
- Copernicus Complexio: high-resolution cosmological N-body simulation
- EAGLE: simulation of galaxy formation and evolution
- Enzo: hydrodynamic simulation system
- FIRE Simulations: high resolution simulation of galaxies
- FLASH: hydrodynamic simulation system
- FORNAX: hydrodynamics simulation software
- GADGET-2: an n-body/SPH simulation computer program
- Gasoline: an SPH code
- GERLUMPH: hardware/software simulator of lensing light curves
- GR1D: core collapse supernova simulation in 1D with GR
- Hyperion: Monte Carlo radiative transfer code
- Illustris Project: 2013-2015 series of cosmological simulations
- LA-COMPASS: MHD-capable hydrodynamic code
- MOCCA: code to model the evolution of stellar clusters
- PLUTO Code: fluid-dynamic simulation code
- PROMETHEUS/VERTEX: hydrodynamic simulation system
- RADEX: radiative transfer code
- RAMSES: hydrodynamic simulation system
- RHAPSODY: simulation of galaxy cluster dark-matter halos
- Romulus simulations: cosmological-simulation project active since circa 2015
- STARBURST99: software to simulate star-forming galaxies
- STARFORGE: star formation simulation code
- Turtlebeach: radiative transfer code
- simulations
- simultaneity: see relativity
- Simultaneous Quad Infrared Imaging Device: NOAO instrument imaging in four infrared bands at once
- SINFONI: see European Southern Observatory Very Large Telescope
- SINS: near-infrared study of distant luminous galaxies
- SINGG (The Survey for Ionization in Neutral Gas Galaxies): survey of HI in galaxies found through the H-alpha line
- single degenerate model: see Type Ia supernova problem
- single degenerate model: see supernova progenitor
- single stellar population (SSP): set of stars born at the same time with the same metallicity
- single-line spectroscopic binary: see double-line spectroscopic binary
- single-line spectroscopic binary: see spectroscopic binary
- single-metallicity stellar population (SSP): set of stars born at the same time with the same metallicity
- single-object slitless spectroscopy: see James Webb Space Telescope
- single-photon avalanche diode (Geiger-avalanche photodiode): type of solid state photon sensor
- single-strand DNA (ssDNA): DNA without the double strand
- singly ionized carbon (C+): ionized carbon missing one electron
- SINGS: see Spitzer Space Telescope
- singular perturbation problem: see perturbation theory
- singularity (gravitational singularity): point where density and gravity reach infinity
- black hole: region of such high mass that light cannot escape
- SINS: near-infrared study of distant luminous galaxies
- SINS/zC-SINF
- SINS: near-infrared study of distant luminous galaxies
- Sinstro: see Las Cumbres Observatory
- SiO (silicon monoxide): compound of silicon and oxygen, one atom each
- SIPS: see rare designator prefixes
- SIR: see SMART-1
- Sirene 2: see Kvant 1
- SIRIUS: see Infrared Survey Facility
- Sirius: brightest star in the sky
- Am star: A-type star with metallic lines
- Sirius A: see Sirius
- Sirius B: see Sirius
- SIRTF (Spitzer Space Telescope): retired infrared space telescope
- SIS: see ASCA
- SIS: see Advanced Composition Explorer
- SIS: see superconducting tunnel junction
- site
- Site 300
- SITELLE: see Canada-France-Hawaii Telescope
- Siv: see rare designator prefixes
- Six-Degree Field Galaxy Survey (6dF Galaxy Survey): UKST survey of galaxies in the southern sky
- Sk: see rare designator prefixes
- SKA (Square Kilometre Array): planned radio telescope with square-kilometer collecting area
- SKA I-low: see Square Kilometre Array
- SKA I-mid: see Square Kilometre Array
- SKA Pathfinder: see Square Kilometre Array
- SKA Precursor: see Square Kilometre Array
- SKA-AAMID: see Square Kilometre Array
- SKA-LOW: see Square Kilometre Array
- SKA-MID: see Square Kilometre Array
- SKA1: see Square Kilometre Array
- SKA1-low: see Square Kilometre Array
- SKA1-mid: see Square Kilometre Array
- SKA2: see Square Kilometre Array
- SKAO (Square Kilometre Array): planned radio telescope with square-kilometer collecting area
- SKBO
- skeleton
- filament: linear volume of high molecular gas density within a galaxy
- SKHB: survey of globular clusters in M31
- SKI: see double star designation
- Skumanich law: see gyrochronology
- Skumanich relationship: see gyrochronology
- sky: see celestial sphere
- Sky & Telescope: amateur astronomy publication
- sky localization (localization): ability to identify location of a transient
- sky quality meter: device to measure the brightness/magnitude of the sky itself.
- sky subtraction: removing background radiation from a telescope observation
- SkyCam: see Liverpool Telescope
- Skylab
- SkyMapper: automated 1.35 m optical telescope in Australia
- SkyMapper Southern Sky Survey (SkyMapper Southern Survey): digital survey of the southern hemisphere sky
- SkyMapper Southern Survey: digital survey of the southern hemisphere sky
- SL (Spacelab): reusable laboratory that was an optional Space Shuttle payload
- SL: see rare designator prefixes
- SLED (spectral line energy distribution): function or plot of brightness of lines in a spectrum
- Slepian window function: see window function
- slew: rotating a telescope to point it
- slew survey: survey conducted by imaging during a telescope's repointings
- slew angle: see slew
- slew observation: see slew survey
- slew speed: see slew
- slew survey: survey conducted by imaging during a telescope's repointings
- commensal mode: telescope usage that accomplishes multiple observations simultaneously
- slew time: see slew
- SLF (super low frequency): electromagnetic radiation, frequency 30 Hz to 300 Hz
- slide rule: see numerical methods
- SLIM: see XRISM
- slim disk: see AGN accretion
- slingshot (gravity assist): method of boosting the speed of a spacecraft
- slit
- slitless spectrograph: spectrograph that does not utilize a slit
- slitless spectrograph: see multi-object spectrograph
- slitless spectrography: see slitless spectrograph
- slitless spectroscopy: see multi-object spectrograph
- Sloan 2.5m Telescope: telescope for SDSS in New Mexico
- Sloan Digital Sky Survey: imaging survey of 500,000,000 objects in 35% of sky
- Sloan Digital Sky Survey V
- Sloan Extended Quasar, ELG, and LRG Survey: see Baryon Oscillation Spectroscopic Survey
- Sloan Extension for Galactic Understanding and Exploration: see Sloan Digital Sky Survey
- Sloan Foundation 2.5m Telescope (Sloan 2.5m Telescope): telescope for SDSS in New Mexico
- Sloan Great Wall: large slab of galaxies discovered in SDSS
- Sloan Supernova Survey: see supernova survey
- SLOTIS: see Livermore Optical Transient Imaging System
- slow irregular variable: see pulsating star
- slow neutron-capture process (s-process): synthesis of elements through neutron capture and beta decay
- r-process: synthesis of elements through neutron capture faster than beta decay
- slow quenching: see quenched galaxy
- slow shock: see shock wave
- slowly-pulsating B-star: B-star with pulsation periods of more than half a day
- SLR: see double star designation
- SLS (Space Launch System): launch rocket in development, e.g., for future astronomical projects
- SLS: see SPIRou
- SLSN (superluminous supernova): stellar explosion larger than a supernova
- SLSN-I: see superluminous supernova
- SLSN-II: see superluminous supernova
- SLSN-R: see superluminous supernova
- SLX: see rare designator prefixes
- SM: see SkyMapper Southern Survey
- Sm: see rare designator prefixes
- SM0313
- SMA (Submillimeter Array): radio interferometer in Hawaii
- SMA: see double star designation
- SMACS: see Massive Cluster Survey
- Small Aperture Telescope: see Simons Observatory
- Small Astronomical Satellite 1 (Uhuru): 1970 X-ray space telescope
- Small Astronomical Satellite program
- Small Astronomy Satellite 2: 1970s NASA gamma ray space telescope
- Small Astronomy Satellite 3: 1970s NASA X-ray space telescope
- Small Bodies Names Committee: old name of IAU Committee for Small Body Nomenclature
- small body (SSSB): solar system body smaller than a dwarf planet
- Small Explorer Program: NASA program for small science spacecraft
- Small Explorers
- NASA: includes space-based astronomy research
- Small IRAIT: see Infrared Telescope Maffei
- Small Magellanic Cloud: dwarf galaxy in the Local Group
- Small Missions for Advanced Research in Technology-1 (SMART-1): Swedish lunar orbiter operational 2003-2006
- small satellite: NASA term for a satellite of 1200 kg or less
- small solar system bodies
- small solar system body (SSSB): solar system body smaller than a dwarf planet
- minor planet: lesser solar system body without comet characteristics
- Small-Sized Telescope: see Cherenkov Telescope Array
- smallsat (small satellite): NASA term for a satellite of 1200 kg or less
- Smart Lander for Investigating Moon: see XRISM
- SMART-1: Swedish lunar orbiter operational 2003-2006
- SMBBH (binary SMBH): co-orbiting supermassive black holes
- SMBH (supermassive black hole): black hole with a mass of millions to billions of solar masses
- SMBH binary (binary SMBH): co-orbiting supermassive black holes
- SMBH formation: process by which SMBHs form
- SMBHB (binary SMBH): co-orbiting supermassive black holes
- SMC (Small Magellanic Cloud): dwarf galaxy in the Local Group
- SMC: see rare designator prefixes
- SMC AB: see rare designator prefixes
- SMC X-1: high-mass X-ray binary with X-ray pulsar
- SMC-N: see rare designator prefixes
- SME (Solar Mesophere Explorer): 1980s Earth atmospheric ozone research satellite
- Smethells: see rare designator prefixes
- SMEX (Small Explorer Program): NASA program for small science spacecraft
- SMEX 15 (PUNCH): 4 microsatellites to observe the Sun
- SMG (submillimeter galaxy): galaxy that produces significant submillimeter radiation
- SMI: see SPICA
- SMI-HRS: see SPICA
- SMI-LRS: see SPICA
- SMI-MRS: see SPICA
- Smith Cloud: high-velocity cloud on collision course with Milky Way
- Smith's Cloud (Smith Cloud): high-velocity cloud on collision course with Milky Way
- Smithsonian Astrophysical Observatory: see Center for Astrophysics
- Smithsonian Astrophysical Observatory Star Catalog (SAO Star Catalog): 1960s catalog
- Smithsonian Institute
- SMM (Solar Maximum Mission): 1980s satellite to study the Sun during solar maximum
- SMM: see submillimeter galaxy designator
- SMNS: see hypermassive neutron star
- smoking gun: convincing piece of evidence
- smooth migration: see planetary migration
- smoothed-particle hydrodynamics: computational method for simulating fluid flows
- SMP: see Hayabusa2
- SMP: see rare designator prefixes
- SMS (supermassive star): star more massive than stars normally form
- SMSS (SkyMapper Southern Survey): digital survey of the southern hemisphere sky
- SMSS 2003-1142 (SMSS J2003-1142): unusual giant star in Milky Way halo
- SMSS J2003-1142: unusual giant star in Milky Way halo
- SMT (Submillimeter Telescope): 10-meter far-infrared telescope
- smuon: see supersymmetry
- SMY: see double star designation
- SN (supernova): stellar explosion larger than a nova
- SN: see signal-to-noise ratio
- SN 1054: see Crab Nebula
- SN 1572: Type Ia supernova noted in 1572 by Tycho Brahe
- SN 1604 (Kepler's Supernova): Type Ia supernova observed in 1604 by Johannes Kepler
- SN 1667: see Cassiopeia A
- SN 1671: see Cassiopeia A
- SN 1680: see Cassiopeia A
- SN 185: supernova recorded in China in AD 185
- SN 1972E
- SN 2014J: Type Ia supernova in Messier 82, the Cigar Galaxy
- SN 1987A: supernova in February 1987 rare for being visible by the naked eye
- SN 1998bw: 1998 supernova with a coincident GRB
- SN 2011fe: see Pinwheel Galaxy
- SN 2014dj
- SN 2014J: Type Ia supernova in Messier 82, the Cigar Galaxy
- SN 2014J: Type Ia supernova in Messier 82, the Cigar Galaxy
- SN 2018cow (AT2018cow): unusual 2018 optical transient
- SN 2018zd
- SN 2019fdr: see AT2019dsg
- SN 2020eyj
- SN 2023af: see International Liquid Mirror Telescope
- SN feedback: see star formation feedback
- SN Hubble diagram: see Hubble diagram
- SN impostor (supernova impostor): extreme stellar explosion that does not destroy the star
- SN light curve (supernova light curve): changing intensity of light following a supernova
- SN progenitor (supernova progenitor): the star or star system that produces a supernova
- SN remnant (supernova remnant): nebula of debris resulting from a supernova
- SN-GRB (GRB-supernova): supernova that produces a GRB
- SNAP (Snapshot Program): short HST observation program aimed to fit between more substantial programs
- Snapshot Program: short HST observation program aimed to fit between more substantial programs
- SNDM
- Snell's law: optical principle of refraction
- refraction: redirection of light passing from one medium to another
- refractive index: measure of how much a material slows down light
- Snell-Descartes law (Snell's law): optical principle of refraction
- sneutrino: see supersymmetry
- SNEWS: see supernova survey
- SNF: see Nearby Supernova Factory
- SNfactory (Nearby Supernova Factory): survey that scanned transient data for supernovae
- SNLS (Supernova Legacy Survey): detect and monitor supernovae to measure the effects of dark energy
- SNO (Sudbury Neutrino Observatory): Canadian underground neutrino detector
- SNO: see SPECULOOS
- SNO+: see Sudbury Neutrino Observatory
- SNOLAB: see PICO experiment
- snow line: distance from protostar so cool that water condenses
- ice: solid state of water
- Snow Solar Tower: see Mount Wilson Observatory
- Snowmass: initiative recommending the next decade's particle physics strategy
- snowplow phase: see supernova remnant
- SNR (signal-to-noise ratio): ratio of the power of a signal to the power of the background noise
- SNR (supernova remnant): nebula of debris resulting from a supernova
- SNR 3C 397 (3C 397): supernova remnant discovered as a radio source
- SNR G111.7-02.1 (Cassiopeia A): supernova remnant visible for 300 years
- SNR G184.6-05.8 (Crab Nebula): supernova remnant in Taurus
- SNR G260.4-03.4 (Puppis A): supernova remnant bright in X-ray
- SNR G263.9-03.3 (Vela supernova remnant): nearby supernova remnant
- SNR G276.5+19.0 (Antlia SN Remnant): dispersed supernova remnant in the constellation Antlia
- SNR G315.0-02.3: see SN 185
- SNT (Schmidt-Newton telescope): type of reflector telescope
- SNU (solar neutrino unit): unit for the detection rate of neutrino detectors
- SO (Simons Observatory): CMB observatory on Atacama Desert
- SO: see rare designator prefixes
- SO2
- Venus: second inner-most planet in the solar system
- SOAR (SOAR Telescope): 4.1 m reflector telescope in Chile
- SOAR Telescope: 4.1 m reflector telescope in Chile
- SOARD (Steward Observatory Asteroid Relational Database): 1980s/1990s repository of asteroid data
- Sobolev approximation: tractable model used in specific kinds of spectral line analysis
- Sobolev length: see Sobolev approximation
- Société astronomique de France: French non-profit astronomical society
- Sociedad Astronómica de Valparaíso y Viña del Mar: Chilean amateur astronomy society
- Society of Amateur Radio Astronomers: US organization
- SODART: see Spektr-RG
- sodium: metal, Na, atomic number 11
- globular cluster: spherical group of stars orbiting a galaxy
- nitrite: ion of a nitrogen atom and two oxygen atoms with extra electron
- sodium hydroxide
- hydroxyl: one hydrogen atom and one oxygen atom bound together
- sodium lamp
- light pollution: light from cities that interferes with astronomical observation
- sodium nitrite: see nitrite
- SOFI: see New Technology Telescope
- PESSTO: NTT survey following up on transients
- SOFIA: aircraft-based infrared observatory
- soft
- Heggie-Hills law: hard binary stars generally get harder when encountering a third star
- soft binary: see hardness
- soft EoS: see equation of state
- soft gamma repeater: object that produces repeated gamma-ray bursts
- soft gamma-ray repeater
- magnetar: neutron star with a strong magnetic field
- soft X-ray: see X-ray
- XEUV: electromagnetic radiation in the range of 0.15-124 nm
- soft X-ray and extreme ultraviolet (XEUV): electromagnetic radiation in the range of 0.15-124 nm
- Soft X-ray Background Radiation Investigation: see OSO 8
- soft X-ray source: see X-ray source
- soft X-ray transient: see transient
- softness: see hardness
- software
- ADAM: procedure to retrieve the shape of an asteroid
- ADAM::THOR: computerized system for discovering asteroids in observation data
- AREPO: cosmology simulation using moving mesh technique
- Astrid simulation: cosmological simulation over z = 99 to 3
- AstroBEAR: MHD simulation system
- Astrocats: software to create and manage an astronomy catalog
- Astronomical Image Processing System: software for processing radio astronomy data
- Astrophysics Multi-spectral Archive Search Engine: 1990s search tool
- astropy: general Python package for astrophysical research
- ATLAS Stellar Model: computer model of a stellar photosphere
- Bolshoi simulation: cosmological simulation
- BT-Settl: model atmosphere of small stars and brown dwarfs
- CASA: software package for radio interferometry image generation
- Castro: hydrodynamics simulation software
- Chandra Interactive Analysis of Observations: software for analyzing Chandra X-ray data
- ChaNGa: cosmological-simulation project active since circa 2015
- CMBFAST: software to calculate CMB anisotropies
- CMFGEN: RT code designed to handle significant stellar wind
- code: astrophysical modeling computer program
- COMPAS: SPS code for compact object binaries
- corner.py: Python library for scatter plot matrices
- DAOPHOT: 1980s CCD photometry software
- DISORT: simulation of radiative transfer in an atmosphere
- dynesty: code for comparing the applicability of multiple models
- EAGLE: simulation of galaxy formation and evolution
- Enzo: hydrodynamic simulation system
- ExoCTK: collection of software for exoplanet observation and analysis
- FIRE Simulations: high resolution simulation of galaxies
- FLASH: hydrodynamic simulation system
- FORNAX: hydrodynamics simulation software
- GADGET-2: an n-body/SPH simulation computer program
- GaiaHub: software to extract proper motions form Gaia and HST data
- Gala: galaxy-formation and evolution software package
- Gasoline: an SPH code
- GitHub: online software development repositories
- Glue: visualization software good for astrophysical data
- GR1D: core collapse supernova simulation in 1D with GR
- Guide Star Astrometric Support Package: software to assist in using guide stars for HST observations
- HEALPix: type of map projection for spheres
- Hyperion: Monte Carlo radiative transfer code
- IDL: interactive vector-oriented programming language
- Illustris Project: 2013-2015 series of cosmological simulations
- Image Reduction and Analysis Facility: NOAO-developed image manipulation/viewing software
- Jupyter: notebook-style programming interface used with Python
- JWST ETC: Python-based exposure time calculator for JWST
- LA-COMPASS: MHD-capable hydrodynamic code
- LasDamas: simulations of large scale evolution of dark matter and galaxies
- lightkurve: software to analyze time series data
- Matplotlib: Python library for plotting
- MESA: collection of stellar astrophysics code
- MITgcm: well-known general circulation model
- mlmapper: software for maximum-likelihood mapmaking
- MOSFiT: code to match light-curves with light-curve models
- NumPy: Python library for numerical programming with arrays
- OpenSpace: visualization software aimed at astrophysical data
- orbitize: planet orbit-fitting software for direct image observations
- Partiview: visualization software aimed at 4D data
- Period04: software to identify periods in time series data
- PHOENIX stellar model: computer model of a stellar photosphere
- PLUTO Code: fluid-dynamic simulation code
- PROMETHEUS/VERTEX: hydrodynamic simulation system
- PyMC: Python package for Bayesian statistical modeling
- RADEX: radiative transfer code
- RAMSES: hydrodynamic simulation system
- RASCALL: efficient code to locate suspected molecular lines
- RHAPSODY: simulation of galaxy cluster dark-matter halos
- ROCKE-3D: rocky-planet-oriented general circulation model
- SciPy: Python library for scientific programming
- showyourwork!: workflow software for reproducible research
- SIMBA: galaxy formation simulation code
- SIMSTACK: software to correlate intensity maps with sources
- Space Telescope Science Data Analysis System: software designed for analysis of HST data
- SPECTRE: an interactive spectrum analysis software package
- STARBURST99: software to simulate star-forming galaxies
- StarTrack: stellar population synthesis code
- SWMF: software package of tools for modeling space weather
- TAM: non-gray-RT 3D model of Titan's atmosphere
- Turtlebeach: radiative transfer code
- U-Net: neural network software for image reconstruction
- Uniview: planetarium software
- WSA-Enlil: computer model of heliosphere for space weather prediction
- XGBoost: machine learning software
- XMM-Newton Science Analysis System: software designed to analyze XMM-Newton X-ray data
- yt: analysis and display software
- software telescope: telescope that depends more than normal upon software for analysis
- software type
- SOHO (Solar and Heliospheric Observatory): satellite observing the Sun
- SOI: see SOAR Telescope
- SOIRDETE: see GI2T
- Sojourner: see Mars Pathfinder
- Sol: see Mars
- Sol: see solar day
- solar
- solar activity: see stellar activity
- Solar and Heliospheric Observatory: satellite observing the Sun
- solar antapex: see solar apex
- solar apex: direction that the Sun is moving compared to nearby stars
- solar arcade (magnetic arcade): series of arch-like magnetic flux lines on the Sun
- solar atmosphere: see stellar atmosphere
- solar cell
- photodiode: class of solid state device to detect EMR
- solar circle: Sun's orbit around the Milky Way
- solar constant: flux from the Sun at 1 AU
- solar core: see stellar core
- solar corona: see corona
- solar cosmic rays: see solar energetic particle
- solar cycle: see sunspot
- solar day: length of a solar system planet or Moon's day
- solar time: time based upon the position of the Sun in the Earth's sky
- synodic period: period until a planet returns to the same position relative to the Sun
- Venus: second inner-most planet in the solar system
- Solar Dynamics Observatory: 2010 satellite observing the Sun
- solar dynamo: see dynamo
- solar eclipse: eclipse consisting of the Moon blocking the Sun from view
- solar energetic particle: high-energy particles from the Sun
- solar energetic particle event (solar particle event): episode of higher velocity solar wind
- solar eruption: sudden brightening of the Sun
- solar event (solar storm): general term for events on the Sun
- solar flare: sudden brightening of the Sun
- solar galactocentric distance: see solar circle
- solar gravitational lens: see natural astronomical telescopes
- Solar Influences Data Analysis Center: Royal Observatory of Belgium division on solar weather data
- solar irradiance (insolation): solar energy received per unit area in given time
- solar lithium problem: see lithium
- solar luminosities: see watt
- solar luminosity: luminosity unit representing the luminosity of the Sun
- energy: physical state needed to do something
- Sun: star at center of solar system
- watt: SI unit of power
- solar mass: mass unit representing the mass of the Sun
- solar mass: see mass
- Sun: star at center of solar system
- solar mass parameter: see standard gravitational parameter
- solar mass: mass unit representing the mass of the Sun
- solar maximum: see sunspot
- coronal loop: visible loop extending out of the Sun's surface and back
- Solar Maximum Mission: 1980s satellite to study the Sun during solar maximum
- Solar Mesophere Explorer: 1980s Earth atmospheric ozone research satellite
- solar minimum: see sunspot
- solar model
- solar motion: see solar apex
- solar nebula: cloud of gas and dust that formed the solar system
- solar nebular disk model
- solar neighborhood: Milky Way in the vicinity of the Sun
- solar neutrino: neutrino from the Sun
- solar neutrino problem: see Mikheyev-Smirnov-Wolfenstein effect
- solar neutrino problem: see solar neutrino
- solar neutrino unit: unit for the detection rate of neutrino detectors
- solar neutrinos
- solar noon (local noon): time at a locality when the Sun is at its highest
- solar noon: see solar time
- equinox: point-in-time when tilt of Earth is neither toward nor away from the Sun
- Solar Orbiter: space probe investigating the Sun's surface and the heliosphere
- solar particle: particles from the Sun such as the solar wind
- solar particle event: episode of higher velocity solar wind
- solar physics: study of the physics of the Sun
- solar powered satellite: concept for a satellite to collect and transfer energy to Earth
- Solar Probe (Parker Solar Probe): space probe investigating solar corona
- Solar Probe Plus (Parker Solar Probe): space probe investigating solar corona
- Solar Probe+ (Parker Solar Probe): space probe investigating solar corona
- solar prominence: see solar eruption
- solar proton event (solar particle event): episode of higher velocity solar wind
- solar radius: see Sun
- solar seismology: see asteroseismology
- solar storm: general term for events on the Sun
- space weather: varying conditions in space affecting Earth and humans
- Solar Storm of 1859 (Carrington event): solar storm September 1-3 1859
- solar switchback (magnetic switchback): Z-shaped magnetic field lines
- solar system: the Sun and what's gravitationally bound to it
- solar system body (solar system object): the Sun, solar system planets, minor planets, comets, and moons
- solar system ephemerides: see ephemeris
- solar system object: the Sun, solar system planets, minor planets, comets, and moons
- solar telescope: telescope designed to observe the Sun
- Solar Terrestrial Relations Observatory (STEREO): two-satellite system to observe the Sun
- solar time: time based upon the position of the Sun in the Earth's sky
- solar transition region (transition region): middle layer of the Sun's atmosphere
- solar variation: see sunspot
- solar weather: see space weather
- solar wind: charged particles emanating from the Sun
- SOLAR-A
- Solar-flux monitor
- solar-like oscillations: see asteroseismology
- solar-wind particles: see solar wind
- SoLEXS: see Aditya-L1
- solid angle: three-dimensional analog of an angle
- field of view: angular measure of how much an optical instrument can view
- solid state detector: see particle spectrometer
- SolO (Solar Orbiter): space probe investigating the Sun's surface and the heliosphere
- SoloHI: see Solar Orbiter
- SOLSTICE: see Upper Atmosphere Research Satellite
- solstice: moment when Sun reaches its northern- or southern-most position
- Soltan argument: distant quasars imply SMBHs still exist
- Sombrero Galaxy: striking spiral galaxy with very large bulge
- Son of X-Shooter
- PESSTO: NTT survey following up on transients
- Sondage Infrarouge de Mouvement Propre (SIMP): 2000s infrared proper-motion survey
- SONEAR (Southern Observatory for Near Earth Asteroids Research): private telescope tracking NEOs
- sonic Mach number: see Mach number
- SOSP: see EURECA
- SOSS: see James Webb Space Telescope
- sound: see sounder
- sound speed: speed at which compression waves traverse a gas
- sound horizon: see baryon acoustic oscillations
- sound speed: speed at which compression waves traverse a gas
- sounder: device to measure something at another depth
- sounding: see sounder
- sounding rocket: sub-orbital rocket to carry out measurements
- source: astronomical object producing some observed signal
- source (radio source): astronomical object producing observable radio
- source confusion: see confusion limit
- source counts (radio source counts): using radio source population characteristics to determine curvature
- source function: measure indicating the effect of a material on EMR passing through
- South Africa
- South African Astronomical Observatory: South African observatory with SALT telescope
- South African Pulsar Timing Array: see MeerKAT Pulsar Timing Array
- South Atlantic Anomaly: see Van Allen belts
- south galactic pole: see galactic north
- South Korea
- COSINE-100: dark matter detection experiment in South Korea
- south node: see orbital element
- South Pole
- ACBAR: instrument used in a CMB survey
- BICEP2: survey to measure the polarization of the CMB
- CMB Stage-4: planned 2020s-generation of ground CMB observations
- DASI: 2000-2003 South Pole CMB telescope
- IceCube: neutrino detector at the South Pole
- QUaD: survey to measure the polarization of the CMB
- South Pole Station: science station at the South Pole
- South Pole Telescope: a millimeter/microwave telescope at South Pole
- South Pole Station: science station at the South Pole
- BICEP2: survey to measure the polarization of the CMB
- QUaD: survey to measure the polarization of the CMB
- South Pole Telescope: a millimeter/microwave telescope at South Pole
- Southeast Asia Astronomy Network: astronomy research/education organization
- Southern African Large Telescope: 10-meter telescope in South Africa
- Southern Astrophysical Research Telescope (SOAR Telescope): 4.1 m reflector telescope in Chile
- Southern Great Wall (Sculptor Wall): large slab of galaxies
- southern lights: see aurora
- Southern Observatory for Near Earth Asteroids Research: private telescope tracking NEOs
- Southern Ring Nebula (NGC 3132): PN of interest in southern sky
- Southern Sky Atlas: see UK Schmidt Survey
- Southern Sky Redshift Survey: 1980s/1990s redshift survey of southern galaxies
- Southern Sky Survey (SkyMapper Southern Survey): digital survey of the southern hemisphere sky
- Southern Stellar Stream Spectroscopic Survey: spectroscopic survey of seven southern-hemisphere stellar streams
- Southern Supercluster
- Southern Wall (Sculptor Wall): large slab of galaxies
- southern zone of avoidance: see zone of avoidance
- Southwest Research Institute: Texas research organization
- SOVA: see EURECA
- SoXS: see New Technology Telescope
- PESSTO: NTT survey following up on transients
- SP: see SELENE
- SP: see rare designator prefixes
- SP77: see rare designator prefixes
- space
- space debris
- GNOSIS: initiative to explore the problem of space debris
- Space Flyer Unit: see IRTS
- Space Force (United States Space Force): US space-related military organization
- Space Infrared Telescope Facility (Spitzer Space Telescope): retired infrared space telescope
- Space Infrared Telescope for Cosmology and Astrophysics (SPICA): plan for a future space IR telescope
- Space Interferometry Mission: past space interferometer plan for parallax and exoplanet detection
- space junk: see Ground-Base Electro-Optical Deep Space Surveillance
- GNOSIS: initiative to explore the problem of space debris
- Space Launch System: launch rocket in development, e.g., for future astronomical projects
- Space Research Organization of the Netherlands: national research institution
- Space Shuttle
- Space Studies Board: National Academy of Sciences unit re astronomy an research via spacecraft
- Space Studies Institute: organization promoting interest in and use of space technology
- Space Surveillance Network (United States Space Surveillance Network): US survey-effort of space objects of interest
- Space Surveillance Telescope: 3.5-m US telescope to discover and monitor objects in space
- LINEAR: survey of near-Earth objects
- Space Telescope (Hubble Space Telescope): observatory-satellite with 2.4-meter reflective telescope
- Space Telescope Science Data Analysis System: software designed for analysis of HST data
- Space Telescope Science Institute: science operator of space telescopes
- MAST: archive of data from surveys and missions
- Space Transport System: early NASA plan for a Space-Shuttle-like vehicle
- space weather: varying conditions in space affecting Earth and humans
- ESA Vigil: plan for space-weather warning satellite at L5
- solar storm: general term for events on the Sun
- WSA-Enlil: computer model of heliosphere for space weather prediction
- Space Weather Modeling Framework (SWMF): software package of tools for modeling space weather
- space weathering: see weathering
- space-like: see spacetime diagram
- geodesic: equivalent to a straight line within curved space
- spacecraft
- Spaceguard Centre: UK private observatory dedicated to NEOs
- SpaceGuard Foundation: private organization to discover and track NEOs
- Spacelab: reusable laboratory that was an optional Space Shuttle payload
- spacetime: four dimensions: time and the three space dimensions
- curvature: unflatness of space
- geodesic: equivalent to a straight line within curved space
- worldline: path of an object through space and time
- spacetime diagram: graph of simplified spacetime, with fewer space dimensions
- spacetime interval: see relativistic invariance
- spacetime interval: see spacetime
- SPACEWATCH: survey to study minor planets
- Spacewatch 1.8-m telescope: see SPACEWATCH
- SpaceX
- SPAD (Geiger-avalanche photodiode): type of solid state photon sensor
- SPADUS: see ARGOS
- spaghettification: see tidal force
- Spain
- SPAN: see Parker Solar Probe
- Spanish
- spar: see solar telescope
- SPARC: see MITgcm
- SPARC/MITgcm: see MITgcm
- SpARCS: see Spitzer Space Telescope
- spark chamber: type of ion detector
- SPARSEPAK: see WIYN 3.5m Telescope
- SPARTAN: series of astronomy satellites launched/retrieved by Space Shuttles
- SPARTAN: see SOAR Telescope
- SPARTAN-201: see SPARTAN
- sparticle: see supersymmetry
- spatial correlation function (N-point function): general term for analyses-techniques of spatial data
- spatial direction: see imaging spectrometer
- spatial Fourier transform
- spatial frequency (wavenumber): reciprocal of wavelength
- spatial heterodyne spectrometer: see heterodyne spectrometer
- spatial pixel: see spaxel
- data cube: three-dimensional array of numerical data
- spatial resolution (angular resolution): measure of a telescope's ability to distinguish spatial detail
- spaxel: like an image-pixel but with a SED for the location
- data cube: three-dimensional array of numerical data
- SPB (slowly-pulsating B-star): B-star with pulsation periods of more than half a day
- SPB: see SuperBIT
- SPC: see Parker Solar Probe
- SPD (spectral power distribution): function of power versus wavelength or frequency
- SPE (solar particle event): episode of higher velocity solar wind
- SpEC: code to solve general relativity problems
- Special Breakthrough Prize: Breakthrough Prize award in addition to the year's annual awards
- special relativity: physics explaining how the speed of light can be constant
- special relativity: see relativity
- blue shift: shortening of wavelengths due to Doppler effects
- cosmological redshift: redshift of distant objects due to the Hubble expansion
- Lorentz transformation: equations describing the effect of relative motion on length and velocity
- mass: object's quality that determines the effects of forces and gravity
- quantum field theory: reworking of quantum mechanics incorporating fields
- redshift: change to longer wavelengths due to Doppler effects
- spacetime: four dimensions: time and the three space dimensions
- worldline: path of an object through space and time
- specific angular momentum: absolute angular momentum divided by mass
- specific heat: ratio of added temperature to added heat for a material
- specific heat capacity (specific heat): ratio of added temperature to added heat for a material
- specific humidity: see humidity
- specific intensity: intensity per unit wavelength or frequency
- specific mean intensity: see specific intensity
- intensity: power reaching a surface from a specific source
- specific star formation rate: see star formation rate
- specific volume: ratio of volume to mass
- specification
- specificity: see balanced accuracy
- Speckle: see Large Altazimuth Telescope
- speckle imager: see speckle imaging
- speckle imaging: method of combining short-term images to yield better resolution
- speckle interferometry (speckle masking): speckle suppression technique using a calculation of the bispectrum
- speckle masking: speckle suppression technique using a calculation of the bispectrum
- speckle noise: see speckle suppression
- speckle suppression: methods of reducing noise in telescope observations
- speckles: image flaws such as extraneous spots
- spectral band: set of related, closely-packed spectral lines
- spectral brightness (specific intensity): intensity per unit wavelength or frequency
- flux density: measure of the strength of a radio signal
- radiance: measure of EMR to/from a solid angle through an area
- spectral class: overall classification of stars based upon spectral features
- A-type star: star with spectral characteristics of around 8500 K
- B-type star: star with spectral characteristics of around 10000-30000 K
- carbon star: star with more carbon than oxygen in its atmosphere
- F-type star: spectral class of star a bit hotter than then Sun
- G-type star: stars spectrally similar to the Sun
- K-type star: spectral class of star a bit cooler than the Sun
- L-type star: spectral type of star cooler than an M-type star
- M-type star: spectral class of star with a temperature in the vicinity of 2500 K
- O-type star: star with spectral characteristics of above 30000 K
- S-type star: type of star with lines indicating zirconium
- spectral type: classification of stars based upon spectral features
- T-type star: brown dwarf with a temperature in the vicinity of 1000 K
- Y-type star: brown dwarf with a temperature less than 700 K
- spectral classification (spectral class): overall classification of stars based upon spectral features
- spectral continuum (continuum): portion of a continuous spectrum not affected by a spectral feature
- spectral correlator: correlator that also functions as a spectrograph
- spectral density: strength of power or energy as a function of frequency
- spectral differential imaging: see speckle suppression
- spectral direction: see imaging spectrometer
- spectral disentangling: see blended spectra
- Spectral Einstein Code (SpEC): code to solve general relativity problems
- spectral emissivity: see emissivity
- spectral energy distribution: function or plot of brightness at each wavelength in the spectrum
- spectral energy distribution fitting: see spectral energy distribution
- Spectral Energy Distribution Machine: see Palomar 60-inch Telescope
- spectral feature: recognizable feature of a spectrum
- spectral feature extraction: see spectral feature
- spectral flux: see radiant flux
- spectral flux density: flux or power of radiation per unit area per unit wavelength
- spectral flux density (flux density): measure of the strength of a radio signal
- spectral index: power by which an object's flux depends on frequency
- spectral intensity (specific intensity): intensity per unit wavelength or frequency
- spectral irradiance (flux density): measure of the strength of a radio signal
- spectral line: dark or bright line in a spectrum
- spectral line broadening (line broadening): processes causing a spectral line to have width
- spectral line designation: labels used to identify spectral lines
- spectral line designator: see spectral line designation
- spectral line energy distribution: function or plot of brightness of lines in a spectrum
- spectral line index
- Lick indices: defined set of spectral line indexes for stars
- spectral line profile: see Voigt profile
- spectral line shape: yields information about source
- spectral line shape: see line shape function
- spectral line tomography (line tomography): using double-peaked spectral lines to place constituents of a disk
- spectral method: method of numerically solving differential equations
- spectral photometry: see photometry
- spectral photon distribution: see spectral power distribution
- spectral pixel: see spaxel
- data cube: three-dimensional array of numerical data
- spectral power distribution: function of power versus wavelength or frequency
- spectral radial velocity: see radial velocity
- spectral radiance (specific intensity): intensity per unit wavelength or frequency
- spectral radiance: see intensity
- spectral radiance: see radiance
- spectral resolution: measure of a spectrograph's ability to resolve features of the spectrum
- spectral retrieval: see retrieval
- spectral signature: spectral characteristics indicating the emitting material and conditions
- spectral temperature: temperature-measure of a source based on a spectrum
- spectral type: classification of stars based upon spectral features
- spectral class: overall classification of stars based upon spectral features
- spectral-line mapping
- SPECTRE: an interactive spectrum analysis software package
- SPECTRE: see IRTF
- Spectro-photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx): all-sky spectral survey space-mission plan
- Spectro-polarimetric High-contrast Exoplanet Research (SPHERE): VLT instrument for imaging exoplanets
- spectro-z: see photometric redshift
- spectrograph: device to record the spectrum of incoming light
- CfA digital speedometer: 1980s/90s spectrograph aimed at radial velocity measurements
- CorMASS: near-infrared spectrograph
- COSIE: EUV spectrograph to analyze the corona
- CRIRES: high resolution IR echelle spectrometer
- Dark Energy Spectroscopic Instrument: new instrument for measuring red-shift of distant objects
- ESIS: EUV spectrograph for solar corona observation
- G-CLEF: spectrograph on the GMT
- HARMONI: spectrograph planned for E-ELT
- HARPS: high-precision spectrograph for exoplanet searches
- HARPS-N: high-precision spectrograph for exoplanet searches in Canary Islands
- HERMES: four-channel spectrograph on the Anglo-Australian Telescope
- Interstellar Medium Absorption Profile Spectrograph: 1980s/1990s UV spectrometer
- Keck Planet Finder: Keck I spectrograph for RV measurements
- KMOS: 2-micron spectrograph on ESO VLT
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- Multi-object Optical and Near-IR Spectrograph: advanced spectrograph under development for VLT
- NEWS: planned near-infrared spectrometer on Discovery Channel Telescope
- NIRPS: near-infrared extension to HARPS spectrograph
- NIRSpec: near infrared spectrograph on JWST
- spectrography: charting the strengths of different electromagnetic wavelengths
- spectrometer: device to measure light by wavelength across its spectrum
- spectroscope: device to study the spectrum of incoming light
- spectroscopy: measurement of light with various electromagnetic wavelengths
- SpeX: a medium-resolution infrared spectrograph
- Subaru PFS: multi-object spectrograph in development for the Subaru telescope
- TAIPAN: multi-object spectrograph with robot fiber-positioner
- TripleSpec: near-infrared spectrograph on the Hale Telescope
- WEAVE: multi-object spectrograph on the WHT
- WFC3: general purpose camera/spectroscope on HST
- Wide-field Multi-object Spectrograph: proposed instrument to detect baryon acoustic oscillations
- WINERED: near-infrared non-cryogenic spectrograph
- spectrography: charting the strengths of different electromagnetic wavelengths
- spectrometer: device to measure light by wavelength across its spectrum
- spectrometers
- spectrometry: measuring the strengths of different electromagnetic wavelengths
- spectrometer: device to measure light by wavelength across its spectrum
- Spectropolarimètre infrarouge (SPIRou): CFHT spectropolarimeter for exoplanet research
- spectropolarimeter: see spectropolarimetry
- Spectropolarimeter for Planetary Exploration
- SpeX: a medium-resolution infrared spectrograph
- spectropolarimetry: measurement of light's polarization by wavelength
- spectroscope: device to study the spectrum of incoming light
- 4MOST: spectrograph in development for VISTA telescope
- spectrograph: device to record the spectrum of incoming light
- spectrometer: device to measure light by wavelength across its spectrum
- spectroscopy: measurement of light with various electromagnetic wavelengths
- TIM: planned balloon-borne 2 m telescope and spectrometer
- Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH): survey of M31's Giant Stellar Stream
- spectroscopic binary: binary star detected by movement indicated by Doppler shifts in the spectrum
- Spectroscopic Imaging Survey in the Near-infrared with SINFONI (SINS): near-infrared study of distant luminous galaxies
- spectroscopic parallax: stellar distance determined through spectroscopy
- spectroscopic phase curve: see phase curve
- Spectroscopic Planet Observatory for Recognition of Interaction of Atmosphere (Hisaki): retired Japanese space ultraviolet telescope
- Spectroscopic Properties of Cool Stars: analysis of spectroscopic data of 7000+ M and L stars
- spectroscopic redshift: see photometric redshift
- spectroscopic retrieval: see retrieval
- Spectroscopic Survey Telescope (Hobby-Eberly Telescope): 10 meter telescope in Texas
- Spectroscopic Terahertz Airborne Receiver for Far-infrared Exploration (TIM): planned balloon-borne 2 m telescope and spectrometer
- Spectroscopic Terahertz observatory: see GUSTO
- Spectroscopic Time-Resolving Observatory for Broadband X-rays (STROBE-X): space X-ray telescope plan
- spectroscopy: measurement of light with various electromagnetic wavelengths
- absorption: removal of photons from a beam of EMR
- spectrograph: device to record the spectrum of incoming light
- spectrometer: device to measure light by wavelength across its spectrum
- spectroscope: device to study the spectrum of incoming light
- spectrum
- absorption line: dark line within a spectrum
- Balmer series: hydrogen lines for electrons settling from n > 2 to n = 2
- Brackett series: hydrogen lines for electrons settling from n > 4 to n = 4
- collisional broadening: line broadening due to nearby particles
- continuous absorption: the absorption of a whole section of a spectrum
- continuous spectrum: smooth spectrum or portion of spectrum with no lines
- Doppler broadening: broadening of spectral lines due to movement of the sources of photons
- emission line: narrow frequency-region of a spectrum with higher intensity
- extreme ultraviolet: electromagnetic radiation in the range of 10-124 nm
- extremely low frequency: electromagnetic radiation, frequency 3 Hz to 30 Hz
- far infrared: infrared radiation with wavelengths in the 30-450 μm range
- gamma rays: electromagnetic radiation, wavelength 10 picometers and less
- H-alpha: hydrogen line for electrons settling from n = 3 to n = 2
- H-beta: hydrogen line for electrons settling from n = 4 to n = 2
- high frequency: electromagnetic radiation, frequency 3-30 MHz
- Humphreys series: hydrogen lines for electrons settling from n > 6 to n = 6
- infrared: light with wavelength too long for our eyes to sense
- integral field unit: instrument to allow a spectrograph to capture data over a 2D field
- K-line: iron X-ray line
- line blanketing: so many bunched spectral lines that they cannot be distinguished
- line broadening: processes causing a spectral line to have width
- Lyman alpha: first line in the Lyman series
- Lyman beta: second line in the Lyman series
- Lyman series: hydrogen series from electrons settling from n > 1 to n = 1
- magnesium lines: spectral lines specific to magnesium
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- mid infrared: infrared radiation with wavelengths in the 7.5-25 μm range
- natural broadening: line broadening due to uncertainty principle
- near infrared: electromagnetic radiation in the range of 750-2500 nm
- OIR: "band name" that means both visible light and infrared
- oxygen lines: spectral lines specific to oxygen
- Paschen series: hydrogen lines for electrons settling from n > 3 to n = 3
- Pfund series: hydrogen lines for electrons settling from n > 5 to n = 5
- radio: electromagnetic radiation, frequency 3 kHz to 300 GHz
- spectral line: dark or bright line in a spectrum
- spectral line designation: labels used to identify spectral lines
- spectral line shape: yields information about source
- spectral power distribution: function of power versus wavelength or frequency
- subradio: electromagnetic radiation, frequency below 3 kHz
- super low frequency: electromagnetic radiation, frequency 30 Hz to 300 Hz
- telluric line: absorption line in ground observation due to Earth atmosphere
- thermal bremsstrahlung: type of EMR produced by thin, hot plasma
- tremendously low frequency: presumably electromagnetic radiation, frequency below 3 Hz
- ultra low frequency: electromagnetic radiation, frequency 300 Hz to 3 kHz
- ultra-high-energy gamma rays: energetic gamma rays with more than 100 TeV photon energy
- ultraviolet: electromagnetic radiation, wavelength 10-400 nm
- UVOIR: a spectral "band name" covering UV, visible light, and IR
- very low frequency: electromagnetic radiation, frequency 3-30 kHz
- very-high-energy gamma rays: energetic gamma rays with 100 GeV to 100 TeV photon energy
- visible light: electromagnetic radiation that our eyes can sense
- water lines: spectral lines specific to water
- X-ray: electromagnetic radiation, wavelength 0.01 to 10 nanometers
- XEUV: electromagnetic radiation in the range of 0.15-124 nm
- spectrum analysis
- SPECTRE: an interactive spectrum analysis software package
- spectrum binary: binary star detectable because its spectrum looks like that of two stars
- spectrum synthesis
- Cloudy: code to model the effect of gas and plasma on spectra
- Spectrum-Roentgen-Gamma
- eROSITA: Russian/German space X-ray telescope launched in 2019
- Spectrum-X-Gamma (Spektr-RG): Russian-German X-ray observatory launched in 2019
- SPECULOOS: search for Earth-like exoplanets orbiting nearby dim stars
- SPECULOOS Northern Observatory: see SPECULOOS
- SPECULOOS Southern Observatory: see SPECULOOS
- SPEDE: see SMART-1
- speed of light: fundamental constant measured as the speed at which light travels
- refraction: redirection of light passing from one medium to another
- refractive index: measure of how much a material slows down light
- speed of light in a vacuum (speed of light): fundamental constant measured as the speed at which light travels
- speed of sound (sound speed): speed at which compression waves traverse a gas
- SpeedyMC: see spectral energy distribution
- Spektr-R: 10 m space radio telescope
- Spektr-RG: Russian-German X-ray observatory launched in 2019
- eROSITA: Russian/German space X-ray telescope launched in 2019
- SPEX
- SpeX: a medium-resolution infrared spectrograph
- SpeX: a medium-resolution infrared spectrograph
- SpeX: see IRTF
- SPF: see star formation
- SPH (smoothed-particle hydrodynamics): computational method for simulating fluid flows
- SPHERE: VLT instrument for imaging exoplanets
- SPHERE: see European Southern Observatory Very Large Telescope
- sphere
- spheroid: sphere-like shape that is flattened or elongated
- SPHEREx: all-sky spectral survey space-mission plan
- spherical aberration: mis-focusing by spherically-curved mirrors and lenses
- spherical astronomy (positional astronomy): calculation methods for relating sky position to position in space
- astrometry: precise measurement of the position and movement of stars
- spherical cow: see back-of-the-envelope calculation
- spherical galaxy
- galaxy: gravitationally-bound group of stars
- spherical harmonic order
- spherical harmonics: harmonic functions on the surface of a sphere
- spherical mirror
- spherical shell: see three dimensional model
- spheroid: sphere-like shape that is flattened or elongated
- paraboloid: circularly-symmetric 3D surface based on parabola
- spheroidal (dwarf spheroidal galaxy): spheroidally-shaped dwarf galaxy lacking star formation
- SPI: see INTEGRAL
- SPICA: plan for a future space IR telescope
- SPICA: see CHARA
- SPICAM: see Mars Express
- SPICAV: see Venus Express
- SPICE: see Solar Orbiter
- spicule: small temporary jet from Sun's surface
- SPIDER: 2015 balloon-borne observatory to observe CMB polarization
- Taurus: balloon-borne polarimeter to study the CMB
- spin: an angular-momentum quantum number
- spin: see particle
- spin quantum number (spin): an angular-momentum quantum number
- spin-down
- spin-down energy
- spin-down luminosity: pulsar's energy extracted from slowing rotation
- spin-down time
- spin-down timescale
- spin-flip transition: see 21-cm line
- spin-orbit resonance: see tidal locking
- Spindle Galaxy: disk galaxy for which we have an edge-on view
- spinel
- CAI: calcium/aluminum specs in chondrites
- spinning dust: see spinning dust emission
- spinning dust emission: source of microwave signal
- spiral
- spiral arm: long, winding visible structure within a spiral galaxy
- spiral density wave: spiral structure that can form in disks
- spiral galaxies
- spiral galaxy: flat galaxy with spiraling arms
- spiral galaxy formation: see spiral galaxy
- spiral nebula
- Kapteyn universe: early 20th century model of the universe centered on the Milky Way
- spiral structure
- SPIRE: see Herschel Space Observatory
- Spirit: see Mars Exploration Rover
- SPIRIT III: see Midcourse Space Experiment
- SPIRITS: Spitzer survey designed to find transients
- SPIRou: CFHT spectropolarimeter for exoplanet research
- SPIRou Legacy Survey: see SPIRou
- Spitzer (Spitzer Space Telescope): retired infrared space telescope
- Spitzer Extended Deep Survey: survey of galaxy mass and black holes through life of the universe
- Spitzer Extragalactic Representative Volume Survey: infrared survey of some well-studied fields
- Spitzer HETDEX Exploratory Large Area Survey: Spitzer-based survey of galaxies
- Spitzer Infrared Intensive Transient Survey (SPIRITS): Spitzer survey designed to find transients
- Spitzer IRAC Shallow Survey (IRAC Shallow Survey): Spitzer survey of moderately wide field
- Spitzer ISS (IRAC Shallow Survey): Spitzer survey of moderately wide field
- Spitzer Space Telescope: retired infrared space telescope
- Spitzer Warm Mission: see Spitzer Space Telescope
- SPLASH: survey of M31's Giant Stellar Stream
- splashback
- splashback radius: see cluster radius
- SPOCK: code to determine stability of orbits
- SPOCS (Spectroscopic Properties of Cool Stars): analysis of spectroscopic data of 7000+ M and L stars
- SPOL: see MMT
- spontaneous emission: see emission
- spontaneous symmetry breaking: see symmetry breaking
- SPRAT: see Liverpool Telescope
- SPRINT-A (Hisaki): retired Japanese space ultraviolet telescope
- Sprite
- Starshot: plan for mission to fly by Alpha Centauri
- SPS (solar powered satellite): concept for a satellite to collect and transfer energy to Earth
- SPS (stellar population synthesis): using spectral characteristics of galaxies to characterize their stellar populations
- SPS: see rare designator prefixes
- A-LIST: catalog of templates of H-band spectra for SPS
- SPS code (stellar population synthesis code): software to perform stellar population synthesis
- SPT (South Pole Telescope): a millimeter/microwave telescope at South Pole
- SPT-3G: see South Pole Telescope
- SPT-CL: see South Pole Telescope
- SPT-SZ: see South Pole Telescope
- SPTpol: see South Pole Telescope
- SQM (sky quality meter): device to measure the brightness/magnitude of the sky itself.
- neutron star: stellar remnant consisting entirely of solar masses of neutrons
- square arcminute: see solid angle
- square degree: see solid angle
- Square Kilometre Array: planned radio telescope with square-kilometer collecting area
- Square Kilometre Array Observatory (Square Kilometre Array): planned radio telescope with square-kilometer collecting area
- Square Kilometre Array Organization: see Square Kilometre Array
- square radian: see solid angle
- squark: see supersymmetry
- SQUID: very sensitive magnetometer
- SQUID (superconducting quantum interference device): type of very sensitive magnetometer using Josephson junctions
- Squid Galaxy (Messier 77): easily-observed spiral galaxy
- SR (special relativity): physics explaining how the speed of light can be constant
- SR: see rare designator prefixes
- SR: see relativity
- SRG (Spektr-RG): Russian-German X-ray observatory launched in 2019
- eROSITA: Russian/German space X-ray telescope launched in 2019
- SRGA: see Spektr-RG
- SRGE: see eROSITA
- SRON (Space Research Organization of the Netherlands): national research institution
- SRR: see MDR/SRR
- SRS: see EnVision
- SRS: see rare designator prefixes
- SRT (Sardinia Radio Telescope): Italian large single-dish radio telescope
- SS (symbiotic binary): giant star transferring mass to a somewhat distant companion
- SS: see Case-Hamburg Survey
- SS: see rare designator prefixes
- SS 433: first microquasar discovered
- SSA: see rare designator prefixes
- SSA22
- SSB (Space Studies Board): National Academy of Sciences unit re astronomy an research via spacecraft
- SSC (synchrotron self-Compton): charged particle cloud scattering its own synchrotron-produced photons
- SSC: see Stardust
- SSD: see particle spectrometer
- ssDNA: DNA without the double strand
- SSE: see ephemeris
- SSFR: see star formation rate
- SSI (Space Studies Institute): organization promoting interest in and use of space technology
- SSI: see Ariel 5
- SSI: see Galileo
- SSI: see Mars Polar Lander
- SSI: see Phoenix
- SSM: see AstroSat
- SSN (United States Space Surveillance Network): US survey-effort of space objects of interest
- SSO (Siding Spring Observatory): observatory in New South Wales, Australia
- SSO (solar system object): the Sun, solar system planets, minor planets, comets, and moons
- SSO: see SPECULOOS
- SSP: set of stars born at the same time with the same metallicity
- SSP: see Cassini
- SSP: see Subaru PFS
- A-LIST: catalog of templates of H-band spectra for SPS
- SSP Survey: see Subaru PFS
- SSRS (Southern Sky Redshift Survey): 1980s/1990s redshift survey of southern galaxies
- SSRS2: see Southern Sky Redshift Survey
- SSS (SuperCOSMOS Sky Survey): survey of stars and galaxies from legacy plates
- SSS (Swope Supernova Survey): survey of low-redshift Type Ia SN light curves
- SSS: see Catalina Sky Survey
- SSS: see HEAO-2
- SSSB: solar system body smaller than a dwarf planet
- minor planet: lesser solar system body without comet characteristics
- SSSBs
- SSSPM: see SuperCOSMOS Sky Survey
- SST (Hobby-Eberly Telescope): 10 meter telescope in Texas
- SST (Space Surveillance Telescope): 3.5-m US telescope to discover and monitor objects in space
- SST (Spitzer Space Telescope): retired infrared space telescope
- SST: see Cherenkov Telescope Array
- SST: see Roque de los Muchachos Observatory
- SSV: see rare designator prefixes
- ST: see double star designation
- ST: see rare designator prefixes
- St (Stokes number): measure of a particle's tendency to follow the flow of a fluid
- Stömgren radius: see Strömgren sphere
- Stability of Planetary Orbital Configurations Klassifier (SPOCK): code to determine stability of orbits
- stability radius: see isolation mass
- stable isotope: see isotope
- stacking: combining images of the same object
- Stampede: research supercomputer at U. Texas
- standard and normal evolution
- standard atomic weight: see element
- standard Big Bang: see Big Bang
- standard candle: astronomical object whose brightness can be determined
- standard cosmology: see alternative cosmologies
- standard deviation (sigma): indication of the confidence level of an experiment
- error bar: feature of a graph to indicate accuracy
- RMS: square root of the average of the squares of some values
- velocity dispersion: statistical dispersion of velocities of a group of objects
- standard error of the mean
- error bar: feature of a graph to indicate accuracy
- standard gravitational parameter: a body's mass times the universal gravitational constant
- standard gravity: see surface gravity
- standard main sequence (zero-age main sequence): describes stars that just began hydrogen fusion
- standard model: model of elementary particles including quarks
- standard model (Lambda-CDM model): Big-Bang cosmological model with a cosmological constant and cold dark matter
- cosmological model: model of the workings and history of the universe
- fiducial: taken as a standard
- flavor: subtype of some type of particle
- quark: type of elementary particle incorporated in protons and neutrons
- standard model of a flare: description of how solar flares function
- standard model of particle physics (standard model): model of elementary particles including quarks
- axion: proposed light, electrically neutral elementary particle
- supersymmetry: extension to standard model of particle physics
- standard reduction potential: see reduction potential
- standard ruler: astronomical phenomenon whose size can be determined
- standard siren: transient whose gravitational waves indicate a specific distance
- standard solar model
- standard source: see photometry
- standard star (telluric star): star of known spectrum used for calibration
- standard star: see photometry
- Stanford University
- Kavli Institute: any of a number of science institutes supported by Kavli Foundation
- star: astronomical body shining from fusion energy
- STAR Academy: Arecbio pre-college program
- star and planet formation: see star formation
- star catalog: see astronomical catalog
- astrometry: precise measurement of the position and movement of stars
- star catalogue: see astronomical catalog
- star class
- star cloud: lighter region of the night sky consisting of a high density of stars
- star cluster (stellar cluster): group of stars apparently formed by a single cloud
- field star: star that is not part of a star cluster
- star clusters
- star count: surveys of stars counting them according to some criteria
- star formation: theorized collapse of gas and dust into stars
- star formation efficiency: see star formation rate
- star formation feedback: mechanisms whereby star formation regulates its own rate
- star formation history: star formation rate as a function of time
- Star Formation in Gaseous Environments (STARFORGE): star formation simulation code
- star formation law (Kennicutt-Schmidt law): relation between gas density and star formation rate
- star formation main sequence (galaxy main sequence): relation between galaxies' star formation and stellar mass
- star formation rate: rate at which material such as gas is turned into stars
- star formation rate density: see star formation rate
- star forming filament (filament): linear volume of high molecular gas density within a galaxy
- star system: a gravitationally bound set of a few stars
- star type
- star-formation rate stellar-mass ratio: ratio between a galaxy's stellar mass and its SF rate
- star-forming galaxy: see galaxy main sequence
- star-forming galaxy: see starburst galaxy
- star-forming radio galaxy: see radio galaxy
- star-forming region: area forming stars and/or ready for star formation
- STAR-X: plan for a future X-ray space telescope
- StarBug: see TAIPAN
- starburst: see starburst galaxy
- AzTEC-3: very distant starburst galaxy
- HFLS3: very distant starburst galaxy
- M82: nearby starburst galaxy
- NGC 253: spiral galaxy 11 million light-years away
- starburst galaxy: galaxy forming stars at a very high rate
- STARBURST99: software to simulate star-forming galaxies
- StarChip
- Starshot: plan for mission to fly by Alpha Centauri
- Stardust: space mission that collected and returned comet coma dust
- stardust: see presolar grain
- STARE: array of radio telescopes monitoring radio transients
- STARE Telescope: see Teide Observatory
- STARE2: see STARE
- starfield: see asterism
- STARFIRE (TIM): planned balloon-borne 2 m telescope and spectrometer
- STARFORGE: star formation simulation code
- Stargazer: see Orbiting Astronomical Observatory
- Stark broadening: see Stark effect
- Stark effect: electric field influence on spectral lines
- Starlight Attenuation & Reddening Survey of Multiple Occulting Galaxies (STARSMOG): survey of dust in galaxies
- starquake: see quake
- stars
- 8 pc: survey of stars within 8 parsecs, using coronagraph
- A-LIST: catalog of templates of H-band spectra for SPS
- accretion: enlargement of an astronomical body by gravitationally attracting additional mass
- accretion disk: disk around an astronomical body of material that is accreting
- age-metallicity relation: older stars generally have lower metallicity
- age-velocity-dispersion relation: relation between stellar age and peculiar velocity
- Aitken Double Star Catalogue: 1932 catalog with both multiple-star systems and non-orbiting double stars
- All-Sky Compiled Catalogue: 2001 catalog compiled from modern sources
- American Association of Variable Star Observers: organization of amateur observers of variable stars
- APASS: down to 16 magnitude
- asterism: easily recognizable star pattern
- asteroseismology: study of stars through analysis of their pulsation
- Astrographic Catalog: historical star catalog of the whole sky to magnitude 11
- Astronomische Gesellschaft Katalog: 19th/20th century astrometric catalog
- ATLAS Stellar Model: computer model of a stellar photosphere
- atmosphere: gas surrounding astronomical object
- Balmer jump: abrupt change in stellar spectrum at the Balmer series wavelength limit
- BaSTI: database relating isochrones to stellar parameters
- BATC: photometric survey of Milky Way stars
- Bayer designation: star designation consisting of a Greek letter and constellation name
- BCool: project studying stellar magnetism
- Bibliographic Catalog of Variable Stars: listing of references to variable stars
- bipolar outflow: streams of matter from the poles of a protostar
- Bonner Durchmusterung Catalog: well-known astrometric catalog from late 1800s
- Boss General Catalog: 1936 catalog of 30,000 stars
- Bright Star Catalog: early 20th century catalog of 9000 stars
- Bruce Proper Motion Survey: 1941 southern-hemisphere survey catalog of Luyten's
- BT-Settl: model atmosphere of small stars and brown dwarfs
- bulge: denser group of stars within a larger group
- Burnham Double Star Catalogue: 1906 catalog with multiple star systems and non-orbiting double stars
- calcium-rich gap transient: type of explosive event larger than a nova and smaller than a supernova
- California-Kepler Survey: follow-up to Kepler to determine stellar radii
- candidate companion: possible object apparently orbiting a known object
- Carlsberg Meridian Catalogue: series of astrometric catalogs from 19th century on
- Case-Hamburg Survey: 1950s-1970s survey(s) of OB stars
- Catalog of Azzopardi & Vigneau: probable stars in the SMC
- Catalog of Circumpolar Stars: list of over 4000 stars in northern part of the sky
- Catalog of Components of Double and Multiple Stars: 1994 catalog of 74000 such double-star components
- Catalog of Stellar Identification: a compilation of the catalogs, BD, CD, and CPD
- Catalog of Stellar Identifications: 1970s catalog cross referencing existing star catalogs
- Catalogue of Southern Double Stars: 1955 catalog with multiple star systems and non-orbiting double stars
- Catalogues of Fundamental Stars: series of astrometric catalogs from 19th century on
- CFHTLS: surveys of transients and stars
- Chandrasekhar limit: maximum mass of a white dwarf
- chromosphere: middle layer of the Sun's atmosphere
- chromospheric activity index: measure of magnetic activity of a star's chromosphere
- circumstellar disk: disk or ring shaped accumulation of matter around a star
- circumstellar envelope: shell-like cloud surrounding a star
- cold mass accretion: stellar accretion through an accretion disk
- color-color diagram: means of comparing characteristics of stars
- color-magnitude diagram: graph plotting color index to magnitude
- color-period diagram: means of comparing periods of stars at various wavelengths
- convection zone: region of a star transmitting energy through convection
- core collapse supernova: supernova resulting from the collapse of the core of a star
- corona: plasma surrounding a star
- coronal hole: cool, low-density portions of the Sun's corona
- coronal mass ejection: mass of plasma ejected from the Sun
- COROT: observatory-satellite to look for transiting exoplanets and stellar oscillations
- CTIO Upper-Scorpius OB Association Survey: survey of low-mass stars and brown dwarfs
- Dartmouth Stellar Evolution Database: database relating isochrones to stellar parameters
- debris disk: circumstellar disk of dust and debris around a star
- Deep Multicolor Survey: 1990s optical and infrared deep survey
- delay time distribution: characterization of interval from star formation until some type of event
- dredge-up: stellar convection bringing up fused material
- Dunlop Double Star Catalogue: 1829 catalog of double stars viewed from Australia
- dwarf nova: flash of a cataclysmic variable star
- Dynamical Analysis of Nearby Clusters: survey of stars in stellar clusters
- Eddington approximation: approximation of a star's internal EMR's divergence from isotropic
- Eddington luminosity: maximum luminosity at which radiation force overcomes gravity
- ejection: forcing or throwing something out
- electron capture supernova: supernova from collapse of iron-free stellar cores
- evolutionary track: H-R diagram track of the life of a star
- field: adjective meaning "in this field of view but unrelated"
- Flamsteed designation: star designation system dating from 1700s
- flux-weighted gravity-luminosity relationship: method of determining luminosity of distant stars
- Frank Ross's Catalog: high-proper-motion and variable stars catalogued by Frank Ross
- fusor: 2003 proposed term for astronomical objects capable of carrying out fusion
- G-dwarf problem: lack of metal-poor G dwarfs in the Milky Way
- Gaia: astrometry survey satellite launched in 2013
- gaia-kepler.fun: website with Gaia data on Kepler target stars
- GaiaHub: software to extract proper motions form Gaia and HST data
- galactic disk: the "disk" portion of a disk galaxy
- Galactic O Star Catalog: 2000s catalog of O-type stars
- galaxy main sequence: relation between galaxies' star formation and stellar mass
- General Catalogue of Stellar Radial Velocities: 1950s century catalog of 15000 stars with their radial velocities
- General Catalogue of Trigonometric Parallaxes: 1950s catalog of stars with parallax measures
- General Catalogue of Variable Stars: 20th/21st century catalog of 58000 variable stars
- Gliese Catalogue of Nearby Stars: 1950s catalog of stars within 20 parsecs
- Gliese-Jahreiss Catalog: 1991 catalog of stars within 25 parsecs
- globular cluster: spherical group of stars orbiting a galaxy
- Gould's Belt: ring of stars around the sky
- GRB-supernova: supernova that produces a GRB
- Groupe Europáen Observations Stellaires: European organization of variable star observers.
- Guide Star Catalog: catalog of stars to help aim HST
- GYRE: a stellar oscillation code
- gyrochronology: means of estimating stellar age from rotation
- H-R diagram: diagram relating effective temperature to luminosity
- H3 Survey: spectroscopic survey of Milky Way halo stars
- H2O Southern Galactic Plane Survey: survey targeting water masers
- Hamburg/ESO Survey: 1990s southern hemisphere survey aimed at finding quasars
- Hayashi limit: limit on the temperature of a star dependent upon its mass and luminosity
- Hayashi track: H-R diagram track of evolution of some pre-main-sequence stars
- Heggie-Hills law: hard binary stars generally get harder when encountering a third star
- helium flash: helium ignition in a star
- helium runaway: helium fusion positive feedback through its generated heat
- Henry Draper Catalog: early 20th century spectroscopic catalog of stars
- Henyey track: H-R diagram track of stellar evolution after the Hayashi track
- Herschel Double Star Catalog: series of early double star catalogs
- Herz catalog: list of 3000 stars in a strip of the southern sky
- Hess diagram: diagram relating effective temperature to luminosity
- HK Survey: 1985 search for metal poor-stars using calcium lines
- host star: the star associated with a planetary system
- hypercompact stellar system: SMBH with no galaxy but has a tight stellar cluster
- Information Bulletin on Variable Stars: former 1961-2019 publication on variable stars
- initial mass function: function describing initial mass of stars
- instability strip: region of H-R diagram where stars are unstable
- International Variable Star Index: variable star catalog by AAVSO
- interstellar magnetic field: galactic magnetic field between that of stars
- isochronal fitting: method of estimating stellar age from retrievable parameters
- isochrone: line of equal ages on an HRD
- isothermal core: core region of a body of all the same temperature
- Japan Amateur Photoelectric Observers Association: past amateur astronomy collaboration
- kappa mechanism: stellar instability caused by opacity increasing with temperature
- Kepler-Swift Active Galaxies and Stars Survey: X-ray/UV survey of objects within the Kepler field
- kilonova: transient associated with merging neutron stars
- Lépine Shara Proper Motion catalog: 2000s catalog of stars with proper motion
- Lacaille Star Catalog: 1700s catalog of about 10,000 southern hemisphere stars
- LaSilla-QUEST Variability Survey: survey for transients
- Lick indices: defined set of spectral line indexes for stars
- Local Group Galaxy Survey: photometric survey of stars in a number of local group galaxies
- Lowell Proper Motion Survey: 1950s-1970s catalogs of stars with proper motion
- luminosity class: classification of size/luminosity of stars
- luminosity function: function giving number of stars or galaxies at different luminosities
- luminous red nova: red-colored event theorized to be a merger of two stars
- Luyten Double Star Survey: 1940s-1970s catalog of double stars
- Luyten Half-second Catalog: 1979 catalog of 4000 stars with high proper motion
- Luyten Palomar Survey: 1970s catalog of stars with high proper motion
- Luyten Two-Tenths Arcsecond Catalog: 1960 catalog of 9000+ stars with proper motion
- Magellanic Catalogue of Stars: 1980s/1990s survey of stars in Magellanic Clouds
- magnetorotational supernova: type of core collapse supernova
- main-sequence lifetime: length of time that a star remains within the main sequence
- MaNGA Stellar Library: catalog of SEDs of representative stars
- mass fraction: measure of a constituent of a star, cloud, etc.
- mass loss: a star's reduction in mass
- mass-luminosity relation: model relating stellar mass and luminosity
- mass-radius relation: model relating stellar mass and radius
- mass-to-light ratio: measure of a population of stars or region
- MATCH: SFH code
- Max Wolf's catalog of stars with proper motion: early 20th century catalog of 1500 stars
- mean molecular weight: measurement of a gas usual for approximating in gas models
- MESA: collection of stellar astrophysics code
- microquasar: stellar-sized black hole with quasar-like activity
- Milky Way Mapper: SDSS spectrographic survey of Milky Way stars
- MISAO project: search for variable stars and transients
- moving group: observed group of stars with similar motion
- moving-cluster method: method of measuring distance to a nearby star cluster
- multiplicity fraction: fraction of star systems that are multiple-star systems
- MUSCLES: HST UV survey of some M Dwarfs that host exoplanets
- N30 Catalog: 1950s catalog collecting proper motion data from older catalogs
- near-Earth supernova: supernova near enough to Earth to affect it
- New Catalogue of Suspected Variable Stars: catalog from latter half of 20th century catalog
- NOMAD: astrometric star catalog
- north polar sequence: set of stars previously used to define magnitudes
- nova: white dwarf explosion
- OB association: stellar association including O and/or early B class stars
- Oort constants: two constants characterizing local Milky-Way motion
- open cluster: group of stars within a galaxy apparently formed by a single cloud
- pair-instability supernova: type of large supernova
- Palomar-Haro-Luyten Catalog: 1960s catalog of faint blue stars
- Panoramic Imaging Survey of Centaurus and Sculptor: survey of extended halos of two nearby galaxies
- Parker wind: model of the solar wind
- partial ionization zone: portion of some stars where gas is partially ionized
- PHOENIX stellar model: computer model of a stellar photosphere
- photosphere: layer of star from which light propagates
- Pico dos Dias Survey: survey aimed to find T-Tauri stars
- plane-parallel atmosphere: simplified atmosphere model ignoring its curvature around the body
- planetary nebula: glowing gas shell ejected by a red giant
- planetary system: all the planets orbiting a star
- PPM Star Catalogue: 1991 astrometric catalog with proper motions
- protoplanetary nebula: short AGB phase before planetary nebula
- protostar: contracted mass of gas that will become a star
- pseudobulge: like a galaxy bulge only flatter
- quadratic field strength: a measure of a star's varying magnetic field
- quasar: distant, bright object that appears something like a star
- Radcliffe Observatory Magellanic Clouds Catalogue: catalog of stars in
- radiation zone: region of a star transmitting energy through radiative diffusion
- radio supernova: supernova that includes a detectable radio emission
- RECONS: consortium for research on stars near the Sun
- reddening: red appearance of astronomical objects because blue light is attenuated by dust
- Rosseland mean opacity: a useful weighted average of opacities at all the frequencies
- SAO Star Catalog: 1960s catalog
- Schönberg-Chandrasekhar limit: maximum stellar isothermal helium core mass
- Schuster-Schwarzschild model: simplified model of a star's production of absorption lines
- seismic waves: waves broadcast through Earth from earthquakes
- SIMP: 2000s infrared proper-motion survey
- snow line: distance from protostar so cool that water condenses
- solar neighborhood: Milky Way in the vicinity of the Sun
- Southern Stellar Stream Spectroscopic Survey: spectroscopic survey of seven southern-hemisphere stellar streams
- spectral class: overall classification of stars based upon spectral features
- spectral type: classification of stars based upon spectral features
- spectroscopic parallax: stellar distance determined through spectroscopy
- Spectroscopic Properties of Cool Stars: analysis of spectroscopic data of 7000+ M and L stars
- SPLASH: survey of M31's Giant Stellar Stream
- SSP: set of stars born at the same time with the same metallicity
- star cloud: lighter region of the night sky consisting of a high density of stars
- star count: surveys of stars counting them according to some criteria
- star formation: theorized collapse of gas and dust into stars
- star system: a gravitationally bound set of a few stars
- STARBURST99: software to simulate star-forming galaxies
- STarSPot: code to model starspots
- stellar activity: transient behavior of a star
- stellar age determination: methods of estimating a star's age
- stellar association: like a large open cluster but even less tightly bound
- stellar astronomy: astronomy of the birth, structure, variety, evolution, and fate of stars
- stellar atmosphere: photosphere and above
- stellar birth rate function: function describing the birth rate of stars by mass
- stellar cluster: group of stars apparently formed by a single cloud
- stellar core: the middle of a star
- stellar demographics: statistics regarding the number of stars
- stellar designation: identifiers for stars
- stellar distance determination: methods by which the distance to a star is determined
- stellar dynamics: stars' gravitational interaction
- stellar encounter: stars passing close to each other
- stellar evolution: the pattern of a star's changing structure over its life
- stellar flare: sudden brightening of a star
- stellar halo: the lesser number of nearby stars surrounding a galaxy
- stellar kinematics: science of the movement of stars
- stellar luminosity determination: methods by which the luminosity of a star is determined
- stellar mass determination: methods by which the mass of a star is determined
- stellar merger: two stars combining into one
- stellar model atmosphere: simulation of the star's production of emitted EMR
- stellar overdensity: portion of galactic halo with more stars than normal
- stellar parameter determination: methods by which the parameters of stars are determined
- stellar population synthesis: using spectral characteristics of galaxies to characterize their stellar populations
- stellar population synthesis code: software to perform stellar population synthesis
- stellar radius determination: methods by which the radius of a star is determined
- stellar rotation: rotation of a star around an axis through the middle
- stellar stream: long group of co-moving stars
- stellar structure: the presumed internal structure of stars
- stellar temperature determination: methods by which the temperature of a star is determined
- stellar wind: gas or plasma emanating from a star
- stellar-mass black hole: black hole that is a stellar remnant
- Struve Catalogs: two catalogs of double stars
- substellar point: point on a body such that a particular star is at the zenith
- sunspot: temporary darker region of the Sun's surface
- SuperCOSMOS Sky Survey: survey of stars and galaxies from legacy plates
- superluminous supernova: stellar explosion larger than a supernova
- supernova: stellar explosion larger than a nova
- supernova impostor: extreme stellar explosion that does not destroy the star
- surface abundance: quantity such as mass per surface area
- surface gravity: measure of gravity at the surface of a body
- surface temperature: temperature of the surface of a star or planet
- synthetic spectrum: simulated spectrum, e.g., of a type of star
- T association: stellar association with T-Tauri stars
- T4 Automated Photometric Telescope: automated 75-cm telescope to a long-term star monitoring survey
- Taurus-Auriga Complex: nearby star-forming region
- thermal pulse: pulse in an AGB star due to helium fusion in a shell
- thermal runaway: situation where heat triggers more heat production
- tidal capture: bodies entering orbit through dissipation of energy by tides
- Tolman-Oppenheimer-Volkoff limit: maximum mass of a neutron star
- traditional approximation of rotation: approximation of waves on a rotating body
- turn-off point: point in H-R diagram of a cluster where stars turn red
- Two Micron All-sky Survey: near-infrared survey of both hemispheres
- Two Micron Sky Survey: 1969 infrared catalog produced by Caltech
- two-stream approximation: approximation of a star's internal EMR's divergence from isotropic
- Type Ia supernova: type of supernova for which distance can be determined
- USNO CCD Astrograph Catalog: USNO star catalog including proper motions
- variable star designation: Bayer system variant for variable stars
- velocity kick: substantial acceleration from a supernova
- velocity-metallicity relation: higher stellar velocity correlates with lower metallicity
- VLT-FLAMES Tarantula Survey: VLT spectroscopic survey of massive stars
- Vogt-Russell theorem: proposition that a star's structure depends on its mass and makeup
- Washington Double Star Catalog: modern database of double stars
- Whole Earth Telescope: international initiative to gather variable star lightcurves
- Wilson-Bappu effect: a relation between a star's spectral line and luminosity
- wind-momentum luminosity relationship: method of determining luminosity of distant stars
- WINGS: all-sky survey investigating known galaxy clusters
- Working Group for Planetary System Nomenclature: IAU group on terminology regarding planetary systems
- XZ Catalog of Zodiacal Stars: 1977 catalog of stars near the ecliptic
- Yale Observatory Zone Catalog: mid-20th century catalogs totaling 400,000 stars
- Zanstra method: method of determining temperature of a hot star within a nebula
- zero-age main sequence: describes stars that just began hydrogen fusion
- [α/Fe] versus [Fe/H] diagram: diagram indicating stars' degree of alpha enhancement
- StarScan machine: see plate measuring machine
- starshade: spacecraft to block light from a specific body
- Starship
- Starshot: plan for mission to fly by Alpha Centauri
- STARSMOG: survey of dust in galaxies
- STarSPot: code to model starspots
- starspot: see sunspot
- StarTrack: stellar population synthesis code
- state of excitation: energy level of something above the minimum
- state of ionization: difference in an ion's electron count versus proton count
- state of matter
- STATIC: see MAVEN
- static limit: see black hole
- static surface: see black hole
- statics: see mechanics
- station keeping (stationkeeping): spacecraft operation to keep it in its orbit
- stationkeeping: spacecraft operation to keep it in its orbit
- statistical dispersion: see velocity dispersion
- statistical equilibrium: see local thermodynamic equilibrium
- statistical isotropy (isotropy): uniformity in all directions
- statistical mechanics: mechanical behavior based upon probability
- statistical physics (statistical mechanics): mechanical behavior based upon probability
- statistical regression
- statistical weight (degeneracy weight): number of quantum states with same energy level
- statistics
- stau: see supersymmetry
- steady state model: see alternative cosmologies
- steady-state universe: see Big Bang
- STEAM: see PUNCH
- steam atmosphere: see water vapor planet
- steam phase: see atmosphere formation
- steam planet (water vapor planet): planet showing water vapor in its atmosphere
- Stefan's constant (Stefan-Boltzmann constant): relates radiation power to temperature and surface area
- Stefan-Boltzmann constant: relates radiation power to temperature and surface area
- Stefan-Boltzmann equation: see Stefan-Boltzmann constant
- Stefan-Boltzmann law: see Stefan-Boltzmann constant
- Stein: see double star designation
- STELLA: two robotic telescopes in Canary Islands
- Stellar Activity (STELLA): two robotic telescopes in Canary Islands
- stellar activity: transient behavior of a star
- stellar age
- stellar age determination: methods of estimating a star's age
- stellar association: like a large open cluster but even less tightly bound
- stellar astronomy: astronomy of the birth, structure, variety, evolution, and fate of stars
- stellar atmosphere: photosphere and above
- stellar BH (stellar-mass black hole): black hole that is a stellar remnant
- stellar birth rate function: function describing the birth rate of stars by mass
- stellar black hole (stellar-mass black hole): black hole that is a stellar remnant
- black hole: region of such high mass that light cannot escape
- collapsar: neutron star or stellar black hole
- stellar evolution: the pattern of a star's changing structure over its life
- stellar cluster: group of stars apparently formed by a single cloud
- stellar collision (stellar merger): two stars combining into one
- stellar core: the middle of a star
- stellar demographics: statistics regarding the number of stars
- stellar designation: identifiers for stars
- stellar distance
- stellar distance determination: methods by which the distance to a star is determined
- stellar dynamics: stars' gravitational interaction
- stellar encounter: stars passing close to each other
- stellar envelope (stellar atmosphere): photosphere and above
- stellar evolution: the pattern of a star's changing structure over its life
- stellar evolution model: see stellar evolution
- stellar feedback (star formation feedback): mechanisms whereby star formation regulates its own rate
- stellar flare: sudden brightening of a star
- stellar flyby: see flyby
- stellar halo: the lesser number of nearby stars surrounding a galaxy
- galactic halo: spherical region around a galaxy with gas, dark matter, etc.
- stellar intensity interferometer (intensity interferometer): interferometer based upon interference from intensity variations
- stellar intensity interferometry: see intensity interferometer
- stellar isochrone: see isochrone
- stellar jet: see jet
- stellar kinematics: science of the movement of stars
- stellar lifetime (main-sequence lifetime): length of time that a star remains within the main sequence
- stellar luminosity
- stellar luminosity class (luminosity class): classification of size/luminosity of stars
- stellar luminosity determination: methods by which the luminosity of a star is determined
- stellar magnetic field: see magnetic field
- stellar mass
- stellar mass determination: methods by which the mass of a star is determined
- stellar mass loss (mass loss): a star's reduction in mass
- stellar merger: two stars combining into one
- stellar metallicity
- stellar model (stellar structure): the presumed internal structure of stars
- stellar model atmosphere: simulation of the star's production of emitted EMR
- stellar nucleosynthesis: see nucleosynthesis
- stellar nucleus: group of many stars at the center of a galaxy
- stellar nursery (star-forming region): area forming stars and/or ready for star formation
- stellar occurrence rate (stellar demographics): statistics regarding the number of stars
- stellar oscillation
- GYRE: a stellar oscillation code
- stellar overdensity: portion of galactic halo with more stars than normal
- stellar parallax: see parallax
- stellar parameter determination: methods by which the parameters of stars are determined
- Stellar Planet Survey: astrometric search for planets around nearby stars
- stellar population: grouping of stars according to metallicity
- stellar population synthesis: using spectral characteristics of galaxies to characterize their stellar populations
- A-LIST: catalog of templates of H-band spectra for SPS
- BPASS: evolution and population synthesis code for binary stars
- COMPAS: SPS code for compact object binaries
- FSPS: code library for stellar population synthesis
- StarTrack: stellar population synthesis code
- stellar population synthesis code: software to perform stellar population synthesis
- stellar population synthesis code: software to perform stellar population synthesis
- stellar population synthesis model: see stellar population synthesis
- stellar pulsation: see pulsating star
- stellar radio source (radio star): star emitting much radio
- stellar radius
- stellar radius determination: methods by which the radius of a star is determined
- stellar remnant: leftovers from a mainstream star
- stellar remnant BH (stellar-mass black hole): black hole that is a stellar remnant
- stellar remnant black hole (stellar-mass black hole): black hole that is a stellar remnant
- stellar rotation: rotation of a star around an axis through the middle
- stellar seismology (asteroseismology): study of stars through analysis of their pulsation
- stellar spot: see sunspot
- stellar stream: long group of co-moving stars
- stellar streams
- stellar structure: the presumed internal structure of stars
- stellar structure model (stellar structure): the presumed internal structure of stars
- stellar system: see solar system
- stellar system: see star system
- stellar temperature
- stellar temperature determination: methods by which the temperature of a star is determined
- stellar velocity: see stellar kinematics
- stellar wind: gas or plasma emanating from a star
- CMFGEN: RT code designed to handle significant stellar wind
- Parker wind: model of the solar wind
- stellar-cluster collapse
- stellar-mass BH (stellar-mass black hole): black hole that is a stellar remnant
- stellar-mass black hole: black hole that is a stellar remnant
- stellar-mass star-formation rate ratio (star-formation rate stellar-mass ratio): ratio between a galaxy's stellar mass and its SF rate
- stellar-structure equations: see stellar structure
- stellar-wind bubble: see stellar wind
- Stelle Doppie: online database of double stars
- stencil: pattern of input to numerical solutions at a point
- Steph: see rare designator prefixes
- Stephan's Quintet: five galaxies grouped in the sky
- STEPS (Stellar Planet Survey): astrometric search for planets around nearby stars
- steradian: see solid angle
- STEREO: two-satellite system to observe the Sun
- STEREO-1: see STEREO
- STEREO-2: see STEREO
- sterile neutrino: see neutrino
- Sternberg Astronomical Institute
- Sterncatalog für die Zone von 6° bis 10° südlicher Declination für das Aequinoctium 1890 (Herz catalog): list of 3000 stars in a strip of the southern sky
- Steward observatory
- Steward Observatory 0.9-meter Spacewatch telescope: see SPACEWATCH
- Steward Observatory Asteroid Relational Database: 1980s/1990s repository of asteroid data
- STF: see Struve Catalogs
- STFC (Science and Technology Facilities Council, UK): UK research agency
- STH: see double star designation
- StHA: see rare designator prefixes
- stiff EoS: see equation of state
- stimulated emission: emission triggered by received photons
- stimulated emission: see emission
- Einstein coefficients: a substance's probabilities of emission and absorption
- maser: electromagnetic radiation amplified by stimulated emission
- STIS: see Hubble Space Telescope
- STIS: see SWFO-L1
- STIS: see rare designator prefixes
- STIX: see Solar Orbiter
- STJ (superconducting tunnel junction): type of Josephson junction usable in EMR sensors
- Stk (Stokes number): measure of a particle's tendency to follow the flow of a fluid
- StKM: see rare designator prefixes
- STN: see double star designation
- STO: see GUSTO
- STO2: see GUSTO
- stochastic background (gravitational wave background): combination of weak gravitational waves such as from distant sources
- Stock: see rare designator prefixes
- Stokes map: see Stokes parameters
- Stokes number: measure of a particle's tendency to follow the flow of a fluid
- Stokes parameters: means of describing a polarization state
- Stokes shift: see fluorescence
- stop: see Lyot stop
- STPSat 6: see UVSC Pathfinder
- STR: see rare designator prefixes
- Str: see Duus-Newell catalog
- Strömgren photometric system: four-color photometric system devised in 1950s
- Strömgren sphere: sphere of ionized hydrogen around an OB star
- strain (gravitational wave strain): a measure of the magnitude of a gravitational wave
- Strand: see rare designator prefixes
- strange: see flavor
- strange matter: see quark matter
- strange quark: see particle
- strange quark: see quark
- exotic star: term for theoretical stars not made of atoms/ions
- hyperon: exotic type of baryon
- quark matter: matter not made of protons and neutrons but of quarks
- standard model: model of elementary particles including quarks
- strange quark matter: see quark matter
- exotic star: term for theoretical stars not made of atoms/ions
- neutron star: stellar remnant consisting entirely of solar masses of neutrons
- strange star: see exotic star
- strange star: see quark matter
- Strasbourg Astrophysical Data Center (Centre de données astronomiques de Strasbourg): repository of astronomical data
- Strasbourg-ESO Catalog of Galactic Planetary Nebulae: 1992 catalog of 1820 objects
- stratigraphy: study of rock layering
- stratopause: see atmospheric temperature profile
- stratosphere: see atmospheric temperature profile
- Stratospheric Observatory for Infrared Astronomy (SOFIA): aircraft-based infrared observatory
- Stratospheric UV Demonstrator of an Imaging Observatory (STUDIO): balloon-borne 0.5 m ultraviolet telescope
- stray light: unintended light reaching a telescope's sensors
- stray light mitigation: see stray light
- StrayCats: survey of X-ray sources detectable in NuSTAR stray light
- streaming instability: type of interplay between disk gas and solids that brings solids together
- radial drift: inward drift of objects within a protoplanetary disk
- Strehl ratio: measure of optical aberration
- strewn field: region with fragments of a meteor impact
- strewn-field (strewn field): region with fragments of a meteor impact
- strewnfield (strewn field): region with fragments of a meteor impact
- striae: parallel ridges
- string: see string theory
- string theory: type of physics theory bringing together current models
- Stripe 82: SDSS field in southern hemisphere
- stripped SN: see core collapse supernova
- stripped star: star with substantial material removed by a binary companion
- stripped supernova: see core collapse supernova
- stripped-envelope star (stripped star): star with substantial material removed by a binary companion
- stripped-envelope supernova: see core collapse supernova
- STROBE-X: space X-ray telescope plan
- Stromlo: see rare designator prefixes
- strong cosmic censorship: see law of cosmic censorship
- strong CP problem
- axion: proposed light, electrically neutral elementary particle
- strong encounter: see stellar dynamics
- strong encounter: see stellar encounter
- strong force: force that holds quarks and nuclei together
- strong gravitational encounter: see stellar dynamics
- strong gravitational interaction
- strong gravitational lens: see gravitational lensing
- strong gravitational lensing: see weak lensing
- strong interaction (strong force): force that holds quarks and nuclei together
- strong interaction: see N-body problem
- strong lensing: see weak lensing
- strong r-process: see r-process
- Strong Radio Source Surveys (Strong Source Surveys): series of 1970s/1980s 5 GHz surveys
- Strong Source Surveys: series of 1970s/1980s 5 GHz surveys
- strong stellar encounter: see stellar encounter
- strong-field gravity: gravity much stronger than in the solar system such as near a black hole
- strong-field gravity physics
- strongly-coupled QFT: see quantum field theory
- strongly-coupled quantum field theory: see quantum field theory
- strontium
- Am star: A-type star with metallic lines
- Ap star: peculiar type of A star
- StRS: see rare designator prefixes
- structure (stellar structure): the presumed internal structure of stars
- structure formation: formation of dark matter halos, galaxy clusters, and galaxies
- structure of the universe (large scale structure): the universe's structure as in placement of clusters
- Struve: see Struve Catalogs
- Struve 1341 B b (HD 80606 b): hot Jupiter discovered in 2001
- Struve Catalogs: two catalogs of double stars
- STS (Space Transport System): early NASA plan for a Space-Shuttle-like vehicle
- STScI (Space Telescope Science Institute): science operator of space telescopes
- MAST: archive of data from surveys and missions
- STSDAS (Space Telescope Science Data Analysis System): software designed for analysis of HST data
- STSI (Space Telescope Science Institute): science operator of space telescopes
- MAST: archive of data from surveys and missions
- STSP (STarSPot): code to model starspots
- STT: see Struve Catalogs
- STTA: see Struve Catalogs
- Students for the Exploration and Development of Space: student-run organization focused on space exploration
- STUDIO: balloon-borne 0.5 m ultraviolet telescope
- StWr: see rare designator prefixes
- Styx: see Pluto
- sub-brown dwarf: see planetary mass object
- sub-Chandrasekhar mass: see supernova progenitor
- sub-GeV dark matter: a more-massive type of CDM
- sub-halo abundance mapping (SHAM): method of galaxy mock-catalog creation
- sub-halo mass function: see halo mass function
- sub-Neptune (mini-Neptune): planet with characteristics a bit like Earth but more like Neptune
- sub-Neptune: see super-Earth
- sub-threshold gravitational wave: see GW detection
- sub-threshold GW: see GW detection
- Subaru (Subaru Telescope): 8.2 meter telescope in Hawaii
- Subaru Deep Field: survey of a small region of the sky using the Subaru telescope
- Subaru PFS: multi-object spectrograph in development for the Subaru telescope
- Subaru Prime Focus Spectrograph (Subaru PFS): multi-object spectrograph in development for the Subaru telescope
- Subaru Strategic Program: see Subaru PFS
- Subaru Telescope: 8.2 meter telescope in Hawaii
- Subaru XMM Deep Survey (Subaru XMM-Newton Deep Survey): survey using the Subaru telescope and XMM-Newton
- Subaru XMM-Newton Deep Field: see Subaru XMM-Newton Deep Survey
- Subaru XMM-Newton Deep Survey: survey using the Subaru telescope and XMM-Newton
- subduction zone
- Europa: well-known Jupiter moon
- subdwarf: star less bright than the main sequence given its spectral class
- subgiant: slightly larger than normal star
- subgiant branch: see subgiant
- subgrid physics (subgrid-scale physics): shortcuts handling physics on a smaller scale than a simulation's grid
- subgrid-scale physics: shortcuts handling physics on a smaller scale than a simulation's grid
- subgroup (galaxy subgroup): a major galaxy and its satellites
- subgroup: see galaxy group
- subhalo: see dark matter halo
- sublimation: single material phase transition from solid to gas
- submillimeter
- Submillimeter Array: radio interferometer in Hawaii
- submillimeter astronomy: astronomy observation and analysis of borderline infrared EMR
- far infrared: infrared radiation with wavelengths in the 30-450 μm range
- submillimeter galaxy: galaxy that produces significant submillimeter radiation
- submillimeter galaxy designator: designation system of submillimeter galaxies
- submillimeter source: see source
- Submillimeter Telescope: 10-meter far-infrared telescope
- Submillimeter Wave Astronomy Satellite: submillimeter space telescope operating 1998-2004
- submillimeter-selected galaxy (submillimeter galaxy): galaxy that produces significant submillimeter radiation
- submillimetre astronomy (submillimeter astronomy): astronomy observation and analysis of borderline infrared EMR
- Submillimetre Common-user Bolometer Array (SCUBA): submillimeter instrument on James Clark Maxwell Telescope
- submoon (subsatellite): object orbiting a moon
- Suborbital Polarimeter for Inflation Dust and the Epoch of Reionization (SPIDER): 2015 balloon-borne observatory to observe CMB polarization
- subradio: electromagnetic radiation, frequency below 3 kHz
- subsatellite: object orbiting a moon
- subsolar point: see substellar point
- subsonic
- substar (substellar object): star-like object with less mass than a star
- substar: see brown dwarf
- Substellar and Planetary Atmospheric Radiation and Circulation: see MITgcm
- substellar object: star-like object with less mass than a star
- substellar point: point on a body such that a particular star is at the zenith
- subsumption band: see Europa
- SUDA: see Europa Clipper
- Sudbury Neutrino Observatory: Canadian underground neutrino detector
- sudden ionospheric disturbance: see solar storm
- SUFI: see SUNRISE
- sugars
- Lego principle: principle that life is associated with a skew in molecule abundances
- SUGRA (supergravity): combination of general relativity and supersymmetry
- SUGRA: see supersymmetry
- SUIT: see Aditya-L1
- sulci: see Enceladus
- sulfide: see geochemistry
- sulfur: metal, S, atomic number 16
- sulfur dioxide
- Venus: second inner-most planet in the solar system
- Sulfur II: see sulfur
- sulfuric acid
- Venus: second inner-most planet in the solar system
- SUMER: see Solar and Heliospheric Observatory
- summer solstice: see solstice
- SUMSS: see MOST
- Sun: star at center of solar system
- Sun surface features: features on the Sun's surface
- Sun-grazing comet: see long-period comet
- SUNGG: see The Survey for Ionization in Neutral Gas Galaxies
- sunquake: see quake
- SUNRISE: balloon-borne 1 m solar telescope
- SUNRISE I: see SUNRISE
- SUNRISE II: see SUNRISE
- SUNRISE III: see SUNRISE
- sunspot: temporary darker region of the Sun's surface
- sunspot cycle: see sunspot
- Sunspot Index Data Center (Solar Influences Data Analysis Center): Royal Observatory of Belgium division on solar weather data
- sunspot number: see sunspot
- Sunspot Solar Observatory
- sunspots
- Sunyaev-Zel'dovich Array: array of eight 3.5 meter microwave telescopes
- Sunyaev-Zel'dovich effect: type of distortion of the CMB
- super giants: see extra-solar planet
- Super Kamiokande Neutrino Detection Experiment: see Kamioka Observatory
- super low frequency: electromagnetic radiation, frequency 30 Hz to 300 Hz
- super Mercury: like the planet Mercury only larger
- super rotation: see zonal flow
- super-Earth: exoplanet more massive than Earth but substantially less than Neptune
- 55 Cancri e: super-Earth orbiting a Sun-like star
- GJ 1214 b: super-Earth extrasolar planet discovered in 2009
- K2-18b: super-Earth in a habitable zone
- Kepler-452b: Earth-like exoplanet discovered in 2015
- LHS 3844 b: rocky planet in habitable zone of a red dwarf
- mini-Neptune: planet with characteristics a bit like Earth but more like Neptune
- OGLE-2005-BLG-390Lb: probable rocky planet orbiting red dwarf
- Proxima b: exoplanet orbiting Proxima Centauri
- super-Eddington accretion: see Eddington luminosity
- super-Eddington accretion: see accretion
- super-Eddington luminosity: see Eddington luminosity
- super-Jupiters: see extra-solar planet
- Super-K: see Kamioka Observatory
- Super-Kamiokande: see Kamioka Observatory
- Super-LOTIS: see Livermore Optical Transient Imaging System
- super-Neptunes: see extra-solar planet
- super-pressure balloon: see SuperBIT
- Super-pressure Balloon-borne Imaging Telescope (SuperBIT): balloon-borne 0.5-m telescope
- super-puff: see super-Earth
- SuperBIT: balloon-borne 0.5-m telescope
- SUPERBLINK: see Lépine Shara Proper Motion catalog
- superbubble: see shell
- superbubble: see supershell
- SuperCam: see Mars 2020
- SuperCDMS: see Cryogenic Dark Matter Search
- SuperCDMS SNOLAB: see Cryogenic Dark Matter Search
- SuperCDMS Soudan: see Cryogenic Dark Matter Search
- supercluster: cluster of galaxy clusters
- supercluster complex: see galaxy filament
- superclusters
- superconducting fluid
- neutron star: stellar remnant consisting entirely of solar masses of neutrons
- superconducting quantum interference device: type of very sensitive magnetometer using Josephson junctions
- superconducting quantum interference device (SQUID): very sensitive magnetometer
- superconducting tunnel junction: type of Josephson junction usable in EMR sensors
- superconductivity: see Cooper pair
- superconductor
- flux freezing: magnetic field lines becoming attached to plasma they pass through
- superconductor-isolation-superconductor: see superconducting tunnel junction
- supercooled state: see supercooling
- supercooling: cooling water below freezing point without it freezing
- SuperCOSMOS: see SuperCOSMOS Sky Survey
- SuperCOSMOS Hα Survey: see SuperCOSMOS Sky Survey
- SuperCOSMOS Sky Survey: survey of stars and galaxies from legacy plates
- SuperCOSMOS Sky Surveys (SuperCOSMOS Sky Survey): survey of stars and galaxies from legacy plates
- supercritical fluid: state of matter at sufficient pressure and temperature
- superearth (super-Earth): exoplanet more massive than Earth but substantially less than Neptune
- superflare
- superfluid: fluid with no viscosity
- superfluidity: see superfluid
- supergalactic coordinate system: celestial coordinate system system based upon the supergalactic plane
- supergalactic latitude: see supergalactic coordinate system
- supergalactic longitude: see supergalactic coordinate system
- supergalactic plane: see supergalactic coordinate system
- supergiant: very large giant star
- supergiant elliptical galaxy: see giant elliptical galaxy
- supergiant star (supergiant): very large giant star
- supergranulation: see Sun
- supergranule: see Sun surface features
- supergravity: combination of general relativity and supersymmetry
- supergravity: see supersymmetry
- superionic ice: odd state of water at high temperature and pressure
- superionic water (superionic ice): odd state of water at high temperature and pressure
- superionic water ice (superionic ice): odd state of water at high temperature and pressure
- superior conjunction: conjunction of an "superior planet", Mars, Jupiter, etc.
- superior planet: see heliocentric system
- synodic period: period until a planet returns to the same position relative to the Sun
- superluminal motion: faster-than-light movement
- superluminous SN (superluminous supernova): stellar explosion larger than a supernova
- superluminous supernova: stellar explosion larger than a supernova
- supermassive BHMF: see black hole mass function
- supermassive binary black hole (binary SMBH): co-orbiting supermassive black holes
- supermassive black hole: black hole with a mass of millions to billions of solar masses
- binary SMBH: co-orbiting supermassive black holes
- black hole: region of such high mass that light cannot escape
- BlackHoleCam: European project to study black holes
- NGC 1600: elliptical galaxy with large supermassive black hole
- Romulus simulations: cosmological-simulation project active since circa 2015
- supermassive black hole binary (binary SMBH): co-orbiting supermassive black holes
- supermassive black hole mass function: see black hole mass function
- supermassive black holes
- supermassive neutron star: see hypermassive neutron star
- supermassive star: star more massive than stars normally form
- SuperNEMO: see KM3NeT
- supernova: stellar explosion larger than a nova
- AT2018cow: unusual 2018 optical transient
- Kepler's Supernova: Type Ia supernova observed in 1604 by Johannes Kepler
- PSR B0950+08: young pulsar
- SN 1572: Type Ia supernova noted in 1572 by Tycho Brahe
- SN 185: supernova recorded in China in AD 185
- SN 1987A: supernova in February 1987 rare for being visible by the naked eye
- SN 1998bw: 1998 supernova with a coincident GRB
- SN 2014J: Type Ia supernova in Messier 82, the Cigar Galaxy
- Supernova Acceleration Probe
- Supernova Cosmology Project: used supernova data to determine a history of the universe's expansion
- supernova designator: typical designation of supernovae
- Supernova Early Warning System: see supernova survey
- Supernova Factory Galaxy (NGC 2770): spiral galaxy that has shown a number of supernovae
- Supernova H0 for the Equation of State (SH0ES): survey to increase the accuracy of the cosmic distance ladder
- supernova Hubble diagram: see Hubble diagram
- supernova impostor: extreme stellar explosion that does not destroy the star
- Supernova Legacy Survey: detect and monitor supernovae to measure the effects of dark energy
- supernova light curve: changing intensity of light following a supernova
- supernova nucleosynthesis: see nucleosynthesis
- supernova progenitor: the star or star system that produces a supernova
- supernova remnant: nebula of debris resulting from a supernova
- supernova search (supernova survey): survey to identify and/or study supernovae
- supernova survey: survey to identify and/or study supernovae
- supernovae
- superparticle: see supersymmetry
- neutralino: proposed type of particle that might include WIMPs
- superposition: see linear theory
- superradiance: exotic quantum-mechanics light-amplification phenomenon
- superrotating jet: see superrotating wind
- superrotating wind: wind traveling in the same direction as the planet is rotating
- supershell: very large ISM shell-shaped region
- supershell: see shell
- supersonic
- supersonic parachute
- drogue chute: parachute to slow something moving at high speed
- superstring theory: version of string theory including supersymmetry
- supersymmetry: extension to standard model of particle physics
- neutralino: proposed type of particle that might include WIMPs
- PICO experiment: a search for a candidate dark matter particle
- supergravity: combination of general relativity and supersymmetry
- supervoid
- void: empty spaces between large scale structures
- SuperWASP: broad Earth-based search for transiting planets
- WASP-12b: retrograde hot Jupiter discovered in 2008
- WASP-43b: hot Jupiter with especially small orbit
- SuperWASP North
- WASP-33b: hot Jupiter discovered in 2010
- SuperWASP-North: see SuperWASP
- SuperWASP-South: see SuperWASP
- superwind: see stellar wind
- SUPOS: see SUNRISE
- supply-limited weathering: see weathering
- supramassive neutron star: see hypermassive neutron star
- suprathermal: having more energy than would be created by thermal excitation
- suprathermal electron: see suprathermal
- suprathermal ion: see suprathermal
- suprathermal particle: see suprathermal
- suprathermal tail: see suprathermal
- Suprime-Cam: see Subaru Telescope
- Suprime-cam
- surface
- surface abundance: quantity such as mass per surface area
- surface brightness: brightness per unit area of a surface
- surface brightness fluctuation: apparent indication of an elliptical galaxy's distance
- surface brightness fluctuations method: see surface brightness fluctuation
- surface brightness profile: curve of a galaxy's brightness from center to edge
- surface brightness profile: see Sérsic profile
- surface brightness sensitivity: see point source sensitivity
- surface density: quantity such as mass per unit area
- surface error: see wavefront error
- surface gravity: measure of gravity at the surface of a body
- surface gravity determination: see surface gravity
- surface of last scattering: sphere around us from which CMB photons are just reaching us
- surface plasmon: see plasmon
- surface reaction: such as reactions between gas and adjacent liquid
- surface temperature: temperature of the surface of a star or planet
- survey (astronomical survey): project collecting astronomical data
- Survey and Time-domain Astrophysical Research Explorer (STAR-X): plan for a future X-ray space telescope
- survey depth: indication of how far a survey reaches
- survey field: portion of the celestial sphere where a survey's observations aim
- Survey for High-z Absorption Red & Dead Sources (SHARDS): GTC survey in GOODS-N field for quenched galaxies at z = 1 to 2.3
- Survey for Transient Astronomical Radio Emission (STARE): array of radio telescopes monitoring radio transients
- Survey of Ultraviolet Emission in Neutral-Gas Galaxies: see The Survey for Ionization in Neutral Gas Galaxies
- survey region (survey field): portion of the celestial sphere where a survey's observations aim
- survey-based designator: astronomical object designators based on name of survey
- Surveying the Agents of Galaxy Evolution (SAGE): survey of gas and dust in the Magellanic Clouds
- surveys
- astronomical catalog: list of observed astronomical bodies including characteristics
- astronomical survey: project collecting astronomical data
- blind survey: survey conducted independently of prior information
- cadence: period between observations
- CMB surveys: efforts studying the CMB
- completeness: measure of how many of a survey's objects of a certain magnitude have been detected
- deep field: survey field subject to lengthy observation to identify distant galaxies
- deep survey: survey using lengthy observation to identify distant galaxies
- Fsky: fraction of the sky, e.g., what a survey covers
- Hα survey: survey looking for the Hα line, typically to find star formation
- legacy survey: phrase sometimes used in survey names
- MAST: archive of data from surveys and missions
- QUEST: sixteen square-degree survey camera
- redshift space: concept of space using redshift as the radial dimension
- redshift survey: survey of the universe aiming at three dimensions
- scan speed: the speed at which the telescope changes angle on the sky while observing
- slew survey: survey conducted by imaging during a telescope's repointings
- Snapshot Program: short HST observation program aimed to fit between more substantial programs
- star count: surveys of stars counting them according to some criteria
- supernova survey: survey to identify and/or study supernovae
- survey depth: indication of how far a survey reaches
- survey field: portion of the celestial sphere where a survey's observations aim
- survey-based designator: astronomical object designators based on name of survey
- SUSI: optical interferometer in Australia
- SUSI: see SUNRISE
- SUSI-1: see New Technology Telescope
- SUSI-2: see New Technology Telescope
- SUSIM: see Upper Atmosphere Research Satellite
- SUSY (supersymmetry): extension to standard model of particle physics
- Sutherland Observatory: see South African Astronomical Observatory
- Sutherland Observing Station: see South African Astronomical Observatory
- Sutherland Station: see South African Astronomical Observatory
- SUTRI: see Satech-01
- SuWt: see rare designator prefixes
- Suzaku: space X-ray telescope
- SVS: see rare designator prefixes
- SW: see rare designator prefixes
- SW effect (Sachs-Wolfe effect): gravitational redshift of the CMB
- SWA: see Solar Orbiter
- SWAN: see Solar and Heliospheric Observatory
- SWAP: see New Horizons
- SWAPI: see IMAP
- SWAS (Submillimeter Wave Astronomy Satellite): submillimeter space telescope operating 1998-2004
- SWASP (SuperWASP): broad Earth-based search for transiting planets
- SWAVES: see STEREO
- SWCam: see CCAT
- SWE (Sachs-Wolfe effect): gravitational redshift of the CMB
- SWE: see IMAP
- SWEA: see MAVEN
- SWEAP: see Parker Solar Probe
- Sweden
- Swedish
- SMART-1: Swedish lunar orbiter operational 2003-2006
- Swedish Solar Telescope: see Roque de los Muchachos Observatory
- Swedish-ESO Submillimetre Telescope: 1990s 15 m submillimeter telescope in Chile
- Swedish-ESO Submillimetre Telescope: former 15 m radio telescope array in Chile
- sweep signal (chirp): burst of signal rising or falling in frequency
- SWEEPS (Sagittarius Window Eclipsing Extrasolar Planet Search): transit search using HST time
- SWeffect (Sachs-Wolfe effect): gravitational redshift of the CMB
- SWEPAM: see Advanced Composition Explorer
- SWFO-L1: future NOAA space-weather warning satellite
- ESA Vigil: plan for space-weather warning satellite at L5
- SWI: see JUICE
- SWI: see double star designation
- SWIA: see MAVEN
- SWICS: see Advanced Composition Explorer
- SWICS: see Ulysses
- Swift: satellite for studying gamma-ray bursts
- Swift Gamma-Ray Burst Mission (Swift): satellite for studying gamma-ray bursts
- Swift/BAT6 (BAT6): sample of long GRBs
- SWIMS: see Advanced Composition Explorer
- SWIMS: see Subaru Telescope
- SWIMS: see University of Tokyo Atacama Observatory
- swing-by (gravity assist): method of boosting the speed of a spacecraft
- SWiPS: see SWFO-L1
- SWIRC: see MMT
- SWIRE: see Spitzer Space Telescope
- Swiss T70 Telescope: see TRAPPIST
- switchback (magnetic switchback): Z-shaped magnetic field lines
- SWMF: software package of tools for modeling space weather
- SWOOPS: see Ulysses
- Swope Supernova Survey: survey of low-redshift Type Ia SN light curves
- Swope Telescope: see Las Campanas Observatory
- Swordy plot: well-known diagram plotting cosmic ray flux to particle energy
- cosmic rays: very-high-energy particles from beyond the solar system
- SWP: see International Ultraviolet Explorer
- SWR: see International Ultraviolet Explorer
- SwRI (Southwest Research Institute): Texas research organization
- SWS: see Infrared Space Observatory
- SWS: see International Ultraviolet Explorer
- SX Arietis variable: see variable star
- SX Phoenicis variable: see variable star
- SXARI: see variable star
- SXC: see High Energy Transient Explorer
- SXDF: see Subaru XMM-Newton Deep Survey
- SXDS (Subaru XMM-Newton Deep Survey): survey using the Subaru telescope and XMM-Newton
- SXG (Spektr-RG): Russian-German X-ray observatory launched in 2019
- SXI: see Hitomi
- SXI: see THESEUS
- SXP: see rare designator prefixes
- SXPHE: see variable star
- SXR: see X-ray source
- SXS: see Hitomi
- SXT: see AstroSat
- SXT: see Hitomi
- SXT: see Yohkoh
- SXT: see transient
- Sy (Seyfert galaxy): visible active galaxy
- Sy 1: see Seyfert galaxy
- Sy 2: see Seyfert galaxy
- Sy 3: see Seyfert galaxy
- LINER: galaxy nucleus emitting spectral lines for ionized and neutral atoms
- SY-1 (Satech-01): Chinese experimental spacecraft
- Sydney University Molonglo Sky Survey: see MOST
- Sydney University Stellar Interferometer (SUSI): optical interferometer in Australia
- symbiotic binary: giant star transferring mass to a somewhat distant companion
- symbiotic star (symbiotic binary): giant star transferring mass to a somewhat distant companion
- symbol
- Z+: symbol for ion or ion charge
- symbolic regression: automated model-building by tinkering with formulae
- symmetric mass ratio: see chirp mass
- symmetry breaking: loss of symmetry, such as due to loss of stability in a regime change
- symmetry energy: see valley of beta stability
- synapse
- synchro-Compton (synchrotron self-Compton): charged particle cloud scattering its own synchrotron-produced photons
- synchro-Compton catastrophe: see synchrotron self-Compton
- synchronous orbit: orbit with angular velocity matching the rotation of the orbited body
- synchronous rotation: see rotation period
- synchronous rotation: see synchronous orbit
- synchrotron
- synchrotron emission (synchrotron radiation): radiation emitted when high-speed charged particles are accelerated
- synchrotron luminosity: see synchrotron radiation
- synchrotron maser: see maser
- synchrotron radiation: radiation emitted when high-speed charged particles are accelerated
- synchrotron self-absorption: see self-absorption
- synchrotron self-absorption: see synchrotron radiation
- synchrotron self-Compton: charged particle cloud scattering its own synchrotron-produced photons
- synchrotron self-scattering: see synchrotron radiation
- synestia model: see Moon formation
- synodic day (solar day): length of a solar system planet or Moon's day
- synodic period: period until a planet returns to the same position relative to the Sun
- orbital period: length of time for an orbiting object to complete one cycle
- sidereal: relative to the fixed position of the stars
- synodic rotation period (solar day): length of a solar system planet or Moon's day
- synodic rotation period: see rotation period
- synodic period: period until a planet returns to the same position relative to the Sun
- synoptic: general, covering everything
- synoptic astronomy (time-domain astronomy): observing and analyzing changes in astronomical objects
- synoptic astronomy: see synoptic
- synoptic meteorology: see synoptic
- Synthése d'Ouverture en Infra Rouge avec Deux Telescopes: see GI2T
- synthesis (nucleosynthesis): creation of atomic nuclei
- synthesis imaging (aperture synthesis): interferometry to simulate a larger aperture telescope
- Synthesis Telescope
- synthetic aperture radar: method of using moving radar with a stationary target
- synthetic aperture telescope: see aperture synthesis
- synthetic field method: method of testing galaxy opacity
- synthetic photometry: deriving photometry-style data from spectroscopy
- synthetic spectrum: simulated spectrum, e.g., of a type of star
- SYO: see double star designation
- Sys-Rem: algorithm to remove systematics from light curve data
- SysRem (Sys-Rem): algorithm to remove systematics from light curve data
- System Requirements Review: see MDR/SRR
- systematic error: errors with non-random characteristics
- sigma: indication of the confidence level of an experiment
- systematics: see systematic error
- systemic redshift: see systemic velocity
- systemic velocity: average velocity of grouped objects, such as a galaxy
- syzygy: see opposition
- SZ (Sunyaev-Zel'dovich effect): type of distortion of the CMB
- Sz: see rare designator prefixes
- SZ Array (Sunyaev-Zel'dovich Array): array of eight 3.5 meter microwave telescopes
- SZ effect (Sunyaev-Zel'dovich effect): type of distortion of the CMB
- SZ/CMB-Pol: see Fred Young Submillimeter Telescope
- SZA (Sunyaev-Zel'dovich Array): array of eight 3.5 meter microwave telescopes
- SZE (Sunyaev-Zel'dovich effect): type of distortion of the CMB
Index