Term Index (digit or symbol)

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• number: see Flamsteed designation
• number G.: see Flamsteed designation
• ⯓: see astronomical symbol
• 'Alopeke: see Gemini Observatory
• *: see astronomical symbol
• , and accessibility (DEIA): abbreviation used for US government efforts
• , equity (DEIA): abbreviation used for US government efforts
• , inclusion (DEIA): abbreviation used for US government efforts
• Greek letter: see Bayer designation
• ⊕: see astronomical symbol
• ★: see astronomical symbol
• ☉: see astronomical symbol
• ☿: see astronomical symbol
• ♀: see astronomical symbol
• ♁: see astronomical symbol
• ♂: see astronomical symbol
• ♃: see astronomical symbol
• ♄: see astronomical symbol
• ♅: see astronomical symbol
• ♆: see astronomical symbol
• ♇: see astronomical symbol
• ⚳: see astronomical symbol
• ⛢: see astronomical symbol
• α (fractionation factor): isotope-related ratio
• α (right ascension): direction coordinate along celestial equator
• α (spectral index): power by which an object's flux depends on frequency
• α: see alpha disk
• α Aur (Capella): brightest star in Auriga
• α Aurigae (Capella): brightest star in Auriga
• α Car (Canopus): second brightest star in the sky
• α Centauri (Alpha Centauri): nearest star system
• α disk (alpha disk): well-known model of an accretion disk
• α process (alpha process): synthesis of elements through alpha capture
• α² Canum Venticorum variable: see variable star
• α_CO (alpha CO): ratio of CO emissions to H₂
• Å (angstrom): unit of length 10^-10 meters
• β (beta): ratio of plasma pressure to magnetic pressure
• β: see Burnham Double Star Catalogue
• β: see double star designation
• β: see spectral index
• β decay (beta decay): radioactivity such that an electron or positron is emitted
• β Per (Algol): a multiple-star system demonstrating effects of mass transfer
• β Persei (Algol): a multiple-star system demonstrating effects of mass transfer
• β Pic b (Beta Pictoris b): super-Jupiter discovered in 2008
• β Pictoris
• Beta Pictoris b: super-Jupiter discovered in 2008
• βpm: see rare designator prefixes
• χ² test (chi-squared test): statistical significance test
• Δ: see Dunlop Double Star Catalogue
• δ (declination): direction coordinate above/below celestial equator
• Δ²_R: see Lambda-CDM model
• étendue (etendue): measure of how wide and deep a telescope observes
• ε (nuclear energy generation rate): fusion power per unit mass
• ε Eridani (Epsilon Eridani): third nearest visible star system in sky
• ε Ind (Epsilon Indi): nearby star system including two brown dwarf companions
• ε Indi (Epsilon Indi): nearby star system including two brown dwarf companions
• ε_O: see metallicity
  • extremely metal poor galaxy: galaxy of interest for its very low metallicity
• η: see chirp mass
• η Car (Eta Carinae): variable star
• η Orionis
• Orion: well-known constellation in the northern hemisphere
• Γ: see Lorentz transformation
• γ: see Lorentz transformation
• γ: see specific heat
• ℏ: see Planck constant
• κ (opacity): a measure of opaqueness of a material
• κ (permeability): ability of a material to allow fluids to pass through it
• κ: see gravitational constant
• κ-mechanism (kappa mechanism): stellar instability caused by opacity increasing with temperature
• Λ (cosmological constant): force counteracting the universe's inward gravitational pull
• Λ (dark energy): energy theorized to accelerate the expansion of the universe
• Λ: see neutron star merger
• λ (Jeans parameter): ratio measuring a tendency of an atmosphere to escape
• λ (eigenvalue): ratio between a vector and a linear transformation of that vector
• λ (wavelength): distance over which a repeating wave repeats
• λ Boo (Lambda Boötis star): peculiar star with metallicity only with lighter elements
• ΛCDM (Lambda-CDM model): Big-Bang cosmological model with a cosmological constant and cold dark matter
  • sigma-8 tension: Lambda CDM anomaly regarding matter fluctuation
  • structure formation: formation of dark matter halos, galaxy clusters, and galaxies
• ℳ (chirp mass): a reduced-mass-like quantity that relates to gravitational waves
• μ (distance modulus): apparent magnitude minus absolute magnitude
• μ (mass ratio): ratio of masses of two objects such as a binary star
• μ (mean molecular weight): measurement of a gas usual for approximating in gas models
• μ (standard gravitational parameter): a body's mass times the universal gravitational constant
• μFUN (MicroFUN): observers following up on microlensing events in the galactic bulge
• μGal: see Gal
• μK: see kelvin
• ν (frequency): number of cycles per unit of time, such as waves per second
• ν (neutrino): light, electrically neutral elementary particle
• ν (wavenumber): reciprocal of wavelength
• ν_τ (tau neutrino): neutrino flavor that becomes a tau particle during interactions
• Ω (density parameter): ratio of a density with the critical density
• Ω (solid angle): three-dimensional analog of an angle
• Ω: see critical density
• ω: see frequency
• Ω-m: see siemens
• Ω_Λ: see Lambda-CDM model
• Ω_Λ: see density parameter
• Ω₀: see critical density
• Ω₀: see density parameter
• Ω_B: see density parameter
• Ω_b: see Lambda-CDM model
• Ω_bh²: see Lambda-CDM model
• Ω_C: see density parameter
• Ω_c: see critical density
• Ω_D: see density parameter
• Ω_dΩ_c: see Lambda-CDM model
• Ω_dh²: see Lambda-CDM model
• Ω_M: see density parameter
• Ω_m: see Lambda-CDM model
• Ω_R: see density parameter
• Öpik-Oort Cloud (Oort Cloud): cloud of distant comets surrounding the solar system
• Φ (gravitational potential): conceptual field indicating the strength of gravity at each point
• Φ (magnetic flux): measure of magnetism passing through a surface
• Φ: see double star designation
• Φ_Tidal: see tide
• π (pion): first type of meson discovered
• ρ_c (critical density): density of the universe which leaves it flat
• Σ (surface density): quantity such as mass per unit area
• Σ: see Struve Catalogs
• σ (Stefan-Boltzmann constant): relates radiation power to temperature and surface area
• σ (sigma): indication of the confidence level of an experiment
• σ (velocity dispersion): statistical dispersion of velocities of a group of objects
• σ-8 tension (sigma-8 tension): Lambda CDM anomaly regarding matter fluctuation
• σ8: see sigma-8 tension
• τ (Thomson optical depth): a measure of effects of Thomson scattering
• τ (optical depth): a measure of opaqueness of a path of light
• τ (pulsar characteristic age): approximate age determination of a pulsar based upon rotation rate
• τ (timescale): general length of time something takes
• τ: see Lambda-CDM model
• τ_advec: see advection
• τ_KH (Kelvin-Helmholtz timescale): time that would radiate away a body's heat energy given its luminosity
• τ_T (Thomson optical depth): a measure of effects of Thomson scattering
• ϒ (mass-to-light ratio): measure of a population of stars or region
• ζ Aurigae
• binary star: system of two stars co-orbiting
• ζ Aurigae system: see binary star
• 'Oumuamua (Oumuamua): small body that passed through the solar system in 2017
• (706765) 2010 TK₇ (2010 TK₇): asteroid that is an Earth Trojan
• μ: see permeability
• a (semi-major axis): maximum radius of an ellipse
• b: see semi-major axis
• e (eccentricity): degree to which an orbit is non-circular
• i: see complex number
• l: see spherical harmonics
• m: see spherical harmonics
• ¹³⁰Te
• CUORE: experiment to sense neutrinoless double beta decay
• ¹³⁶Xe
• EXO: experiment to detect neutrinoless double beta decay in xenon
• ¹³CO: see carbon monoxide
• ¹H: hydrogen isotope with no neutrons
• ¹H burning (hydrogen burning): any fusion reaction starting with hydrogen
• ¹hydrogen (¹H): hydrogen isotope with no neutrons
• ²H (deuterium): hydrogen isotope with one neutron
• ³H: see deuterium
• ³H: see hydrogen
  • KATRIN: experiment to measure neutrino mass
  • Project 8: experiment in development to measure neutrino mass
• ⁴⁴Ti: see titanium
  • supernova light curve: changing intensity of light following a supernova
• ⁵⁶Co
• supernova light curve: changing intensity of light following a supernova
• ⁵⁶Ni
• supernova light curve: changing intensity of light following a supernova
• ⁶⁰Co
• supernova light curve: changing intensity of light following a supernova
• [α/Fe]: see alpha-enhanced
• [α/Fe] versus [Fe/H] diagram: diagram indicating stars' degree of alpha enhancement
• [CH] (methylidyne): compound of one carbon and one hydrogen atom
• [CII] (ionized carbon fine structure line): carbon line that traces distant star formation
  • carbon: element, C, atomic number 6
  • CONCERTO: spectrometer aimed at mapping the [CII] line
  • EXCLAIM: planned balloon-borne 70-cm telescope with spectrometers
  • fine structure: separate spectral lines due to electron spin and relativistic effects
  • Millimeter-wave Intensity Mapping Experiment: project to map CO and [CII]
  • self-absorption: EMR absorption by the same substance that emitted it
  • TIM: planned balloon-borne 2 m telescope and spectrometer
  • Tomographic Ionized-carbon Mapping Experiment: instrument in development to map the [CII] line
• [CI]: see fine structure
  • carbon: element, C, atomic number 6
• [Fe II]: see iron
• [Fe/H]: see iron
• [HI]
• neutral atomic hydrogen: state of hydrogen when sufficiently cool
• [N III]
• Cosmic Dawn Intensity Mapper: NASA concept for space telescope for intensity mapping
• [NII]
• TIM: planned balloon-borne 2 m telescope and spectrometer
• [O III]
• Cosmic Dawn Intensity Mapper: NASA concept for space telescope for intensity mapping
• planetary nebula luminosity function: model used in distance estimation
• [O/Fe]: see alpha-enhanced
• 0ES: see HEAO-2
• 0FGL: see Fermi
• 1 Ceres (Ceres): dwarf planet and largest asteroid
  • asteroid: minor planet without comet characteristics
  • dwarf planet: round like a planet, only smaller
• 1 Jansky Empty Field Survey: 1980s survey to find optical identifications for weak radio sources
• 1 Jy (1 Jansky Empty Field Survey): 1980s survey to find optical identifications for weak radio sources
• 1-point function: see N-point function
• 1.27m Mount Stromlo Telescope
• MACHO Project: survey searching out microlensing that could indicate a MACHO
• 1.3-mm observation: observation frequency useful for detecting dust
• 1.5m Hale Telescope
• coudé focus telescope: type of Nasmyth telescope with additional mirrors
• 1/f noise: see red noise
• 1/V_max method (volume weighting): method of accommodating the Malmquist bias
• 10 Hygiea: see asteroid
• 101955 Bennu: near-Earth asteroid that is the target of a sample-return mission
  • OSIRIS-REx: space mission aiming to return a sample of an asteroid
• 10199 Chariklo: largest minor planet in the outer solar system
• 1050cm: see Parkes Observatory
• 10C: see Cambridge Catalog of Radio Sources
  • Third Cambridge Catalogue of Radio Sources: 1959 catalog of northern hemisphere 159-MHz sources
• 12 scale: see metallicity
  • extremely metal poor galaxy: galaxy of interest for its very low metallicity
• 134340 Pluto (Pluto): dwarf planet formerly listed as one of the nine planets
  • dwarf planet: round like a planet, only smaller
  • Kuiper Belt: further part of solar system beyond Neptune
  • trans-Neptune object: minor planet beyond Neptune
• 136108 Haumea (Haumea): dwarf planet discovered in 2004
  • dwarf planet: round like a planet, only smaller
  • Kuiper Belt: further part of solar system beyond Neptune
  • trans-Neptune object: minor planet beyond Neptune
• 136199 Eris
• dwarf planet: round like a planet, only smaller
• Kuiper Belt: further part of solar system beyond Neptune
• trans-Neptune object: minor planet beyond Neptune
• 136472 Makemake
• dwarf planet: round like a planet, only smaller
• Kuiper Belt: further part of solar system beyond Neptune
• trans-Neptune object: minor planet beyond Neptune
• 13MM: see Parkes Observatory
• 140 Foot Telescope (Green Bank 140 Foot Telescope): West Virginia radio telescope
• 150 megaparsecs
• baryon acoustic oscillations: density fluctuations stemming from acoustic waves in the early universe
• 152830 Dinkinesh
• Lucy: space probe to observe Jupiter Trojan asteroids
• 15760 1992 QB1₁
• Kuiper Belt: further part of solar system beyond Neptune
• 15760 Albion
• Kuiper Belt: further part of solar system beyond Neptune
• 16 Cyg (16 Cygni): triple star system with detected exoplanet
• 16 Cygni: triple star system with detected exoplanet
• 16 Psyche (Psyche): asteroid discovered in 1852
  • Psyche: space mission on its way to asteroid Psyche
• 16-pole: see multipole expansion
• 162173 Ryugu
• Hayabusa2: JAXA mission that returned a sample of an asteroid
• 18 cm line: see hydroxyl
• 1947 sunspot: largest sunspot ever recorded
• 1987A (SN 1987A): supernova in February 1987 rare for being visible by the naked eye
• 1992 QB1₁
• Kuiper Belt: further part of solar system beyond Neptune
• 1999 RQ₃₆ (101955 Bennu): near-Earth asteroid that is the target of a sample-return mission
  • OSIRIS-REx: space mission aiming to return a sample of an asteroid
• 19P/Borrelly
• Deep Space 1: 1998-2001 mission to fly by asteroid
• 1A: see Ariel 5
• 1AGL: see AGILE
• 1C: see Cambridge Catalog of Radio Sources
• 1D climate model (one dimensional climate model): atmospheric model ignoring all horizontal motion
• 1D model: see three dimensional model
  • one dimensional climate model: atmospheric model ignoring all horizontal motion
• 1E: see HEAO-2
• 1E 0657-56 (Bullet Cluster): two galaxy clusters that are colliding
• 1ES: see HEAO-2
• 1FGL: see Fermi
• 1H: see HEAO-1
• 1I/'Oumuamua (Oumuamua): small body that passed through the solar system in 2017
• 1I/2017 U1 (Oumuamua): small body that passed through the solar system in 2017
• 1PN: see post-Newtonian formalism
• 1RXH: see ROSAT
• 1RXP: see ROSAT
• 1RXS: see ROSAT
• 1SAX: see BeppoSAX
• 1SWASP: see SuperWASP
• 1SWASP J140747 (J1407): star eclipsed by a body with a ring system
• 1SWASP J140747.93-394542.6 (J1407): star eclipsed by a body with a ring system
• 1WGA: see rare designator prefixes
• 2 Pallas: see asteroid
• 2-brane: see brane
• 2-point correlation function: see N-point function
• 2-point function: see N-point function
• 2.5 dimensional model: model such as computer simulation between 2D and 3D
• 2.5D model (2.5 dimensional model): model such as computer simulation between 2D and 3D
• 20000 Varuna
• Kuiper Belt: further part of solar system beyond Neptune
• 2001 Mars Odyssey (Mars Odyssey): Mars orbiter launched by NASA in 2001
• 2002 AW₁₉₇
• Kuiper Belt: further part of solar system beyond Neptune
• 2002 TC₃₀₂
• trans-Neptune object: minor planet beyond Neptune
• 2002 TX₃₀₀
• Kuiper Belt: further part of solar system beyond Neptune
• 2002 UX₂₅
• Kuiper Belt: further part of solar system beyond Neptune
• 2003 VB₁₂ (Sedna): distant solar system planetoid discovered in 2003
• 2004 XR₁₉₀
• trans-Neptune object: minor planet beyond Neptune
• 2010 TK₇: asteroid that is an Earth Trojan
• 2012 VB₁₁₃: see Kuiper Belt
• 2014 MU₆₉: see New Horizons
• 21-cm experiment: search for redshifted 21-cm hydrogen emission lines
• 21-cm line: hydrogen line useful for determining redshift
  • 21-cm experiment: search for redshifted 21-cm hydrogen emission lines
  • BINGO: future radio telescope for mapping distant neutral hydrogen
  • Canadian Hydrogen Intensity Mapping Experiment: radio telescope mapping distant neutral hydrogen
  • Dwingeloo Obscured Galaxy Survey: radio survey of ZOA for 21-cm lines indicating galaxies
  • EDGES: survey aiming at highly-redshifted 21-cm detection
  • Fast Fourier Transform Telescope: proposed all-digital telescope with synthetic aperture
  • HERA: low frequency radio telescope
  • HI 4-Pi Survey: HI map based upon EBHIS and GASS
  • HI Jodrell All-Sky Survey: northern-hemisphere HI survey carried out in late 90s/early 2000s
  • HIPASS: HI survey carried out 1997 to 2002
  • HIRAX: radio telescope array for 21-cm surveying
  • Low-frequency Array: low frequency radio telescope
  • Murchison Widefield Array: low frequency radio telescope
  • PAPER: radio interferometer for 21-cm measurement
  • Parkes HI Zone of Avoidance Survey: radio survey to identify galaxies hidden by the zone of avoidance
  • SARAS: survey aiming at highly-redshifted 21-cm detection
  • self-absorption: EMR absorption by the same substance that emitted it
  • spin: an angular-momentum quantum number
  • Tianlai Project: 21-cm line intensity mapping project
• 217.5 nm absorption feature (2175 angstrom feature): prominent absorption feature in ISM
• 217.5 nm feature (2175 angstrom feature): prominent absorption feature in ISM
• 2175 angstrom absorption feature (2175 angstrom feature): prominent absorption feature in ISM
• 2175 angstrom feature: prominent absorption feature in ISM
  • reddening: red appearance of astronomical objects because blue light is attenuated by dust
• 220 nm feature (2175 angstrom feature): prominent absorption feature in ISM
• 243 Ida: see binary minor planet
  • Galileo: circa 1990s space mission to Jupiter
• 25143 Itokawa
• Hayabusa2: JAXA mission that returned a sample of an asteroid
• 25m Dwingeloo Radio Telescope
• Dwingeloo Obscured Galaxy Survey: radio survey of ZOA for 21-cm lines indicating galaxies
• 26-Meter Telescope
• Dominion Observatory 1420 MHz Source Catalog: 1960s survey of northern-hemisphere radio sources
• Dominion Radio Astrophysical Observatory: radio observatory in British Columbia, Canada
• 26P/Grigg-Skjellerup
• Giotto: 1980s space mission carrying out a Comet Halley flyby
• 28978 Ixion
• trans-Neptune object: minor planet beyond Neptune
• 2A: see Ariel 5
• 2C: see Cambridge Catalog of Radio Sources
• 2CG: see Cos-B
• 2D Fourier transform: type of transformation of 2D functions used for analysis and manipulation
• 2D model: see three dimensional model
  • subgrid-scale physics: shortcuts handling physics on a smaller scale than a simulation's grid
• 2dF: see Anglo-Australian Telescope
  • 2dF Galaxy Redshift Survey: imaging survey of 300,000 extragalactic objects
  • 2dF-SDSS LRG and QSO survey: spectroscopic survey of distant galaxies
  • Dark Energy Survey: survey aimed at mapping the universe's expansion
  • DEVILS: visible-light spectrographic survey of 56k distant galaxies
  • fiber positioner: machine to set up fibers in multi-object spectrograph
  • GALAH: survey of Milky Way with an emphasis on old structures
  • Hawaii K-band Galaxy Survey: near-infrared survey of a selection of fields
  • HERMES: four-channel spectrograph on the Anglo-Australian Telescope
  • Southern Stellar Stream Spectroscopic Survey: spectroscopic survey of seven southern-hemisphere stellar streams
  • WiggleZ: survey aimed at mapping dark energy
• 2dF Galaxy Redshift Survey: imaging survey of 300,000 extragalactic objects
• 2dF-SDSS LRG and QSO survey: spectroscopic survey of distant galaxies
• 2dFGRS (2dF Galaxy Redshift Survey): imaging survey of 300,000 extragalactic objects
• 2E: see HEAO-2
• 2EG: see Compton Gamma Ray Observatory
• 2EGS: see Compton Gamma Ray Observatory
• 2EUVE: see Extreme Ultraviolet Explorer
• 2FGL: see Fermi
• 2HWC: see High-altitude Water Cherenkov Observatory
• 2I/Borisov
• Oumuamua: small body that passed through the solar system in 2017
• 2M: see Two Micron All-sky Survey
• 2M1207: brown dwarf with possible exoplanet
• 2MA: see Two Micron All-sky Survey
• 2MASP: see Two Micron All-sky Survey
• 2MASS (Two Micron All-sky Survey): near-infrared survey of both hemispheres
  • JHK photometric system: system to classify stars according to near-infrared colors
• 2MASS 0720-0846 (Scholz's Star): nearby binary star with red dwarf and brown dwarf
• 2MASS 1207: see TW Hydrae association
• 2MASS Extended Source Catalog: see Two Micron All-sky Survey
• 2MASS J00445930-1516166 (LHS 1140): red dwarf with rocky planet in its habitable zone
• 2MASS J02530084+1652532 (Teegarden's Star): nearby red dwarf
• 2MASS J07200325-0846499 (Scholz's Star): nearby binary star with red dwarf and brown dwarf
• 2MASS J12073346-3932539 (2M1207): brown dwarf with possible exoplanet
• 2MASS J15065257+7027247 (WISE 1506+7027): nearby brown dwarf
• 2MASS J16264502-2423077 (Elias 2-27): much-studied YSO
• 2MASS J20020411+4422536 (Kepler-79): star with four super-puff planets
• 2MASS J23062928-0502285 (TRAPPIST-1): red dwarf with exoplanets within the habitable zone
• 2MASS Photometric Redshift Catalog: galaxy redshifts from 2MASS
• 2MASS photometric system (JHK photometric system): system to classify stars according to near-infrared colors
• 2MASS XSC: see Two Micron All-sky Survey
• 2MASSI: see Two Micron All-sky Survey
• 2MASSP: see Two Micron All-sky Survey
• 2MASSW: see Two Micron All-sky Survey
• 2MASX: see Two Micron All-sky Survey
• 2MPZ (2MASS Photometric Redshift Catalog): galaxy redshifts from 2MASS
• 2MUCD: see Two Micron All-sky Survey
• 2PN: see post-Newtonian formalism
• 2QZ: see rare designator prefixes
• 2RE: see ROSAT
• 2RXP: see ROSAT
• 2S: see Small Astronomy Satellite 3
• 2SLAQ (2dF-SDSS LRG and QSO survey): spectroscopic survey of distant galaxies
• 2U: see Uhuru
• 2UCAC: see USNO CCD Astrograph Catalog
• 2XMM: see XMM-Newton
• 3 Juno: see asteroid
• 3-brane: see brane
• 3-mm window
• EMPIRE Survey: survey of gas in M51a to follow up PAWS
• 3-point correlation function: see N-point function
• 3-point function: see N-point function
• 3-simplex
• areal coordinate system: coordinate system based upon a known triangle
• 30 Dor (30 Doradus): HI region in LMC
• 30 Doradus: HI region in LMC
  • SAGE: survey of gas and dust in the Magellanic Clouds
  • VLT-FLAMES Tarantula Survey: VLT spectroscopic survey of massive stars
• 32-pole: see multipole expansion
• 38628 Huya
• Kuiper Belt: further part of solar system beyond Neptune
• 3A: see Ariel 5
• 3C (Third Cambridge Catalogue of Radio Sources): 1959 catalog of northern hemisphere 159-MHz sources
• 3C 10: see SN 1572
• 3C 273: first quasar discovered
• 3C 279: striking variable quasar
• 3C 295: distant radio galaxy
• 3C 303: Seyfert galaxy of interest
• 3C 327: elliptical radio galaxy
• 3C 348: giant elliptical radio galaxy
• 3C 397: supernova remnant discovered as a radio source
• 3C 400 (W51): cloud complex radio source
• 3C 405 (Cygnus A): early-discovered radio galaxy showing a quasar
• 3C 48: radio galaxy/quasar
• 3C 9: first quasar discovered
• 3CR: see Third Cambridge Catalogue of Radio Sources
• 3CRR
• Third Cambridge Catalogue of Radio Sources: 1959 catalog of northern hemisphere 159-MHz sources
• 3D model (three dimensional model): computer simulation handling variation in all three dimensions
  • subgrid-scale physics: shortcuts handling physics on a smaller scale than a simulation's grid
• 3D-HST: near-infrared survey of 100,000 galaxies by HST
• 3EG: see Compton Gamma Ray Observatory
• 3FHL: see Fermi
• 3GM: see JUICE
• 3PN: see post-Newtonian formalism
• 3U: see Uhuru
• 4 Vesta: see asteroid
• 4-brane: see brane
  • Randall-Sundrum model: particular 5-dimensional cosmological model
• 4-metre Multi-object Spectroscopic Telescope (4MOST): spectrograph in development for VISTA telescope
• 4-shooter: see Hale Telescope
• 43 Meter Telescope (Green Bank 140 Foot Telescope): West Virginia radio telescope
• 469219 Kamo'oalewa: see quasi-satellite
• 47 Tuc (47 Tucanae): bright globular cluster
• 47 Tucanae: bright globular cluster
• 47171 Lempo
• trans-Neptune object: minor planet beyond Neptune
• 4C (Fourth Cambridge Catalog of Radio Sources): 1960s catalog of northern hemisphere 178 MHz sources
• 4C Array: see Fourth Cambridge Catalog of Radio Sources
  • Mullard Radio Astronomy Observatory: radio observatory near Cambridge, UK
• 4CT: see Fourth Cambridge Catalog of Radio Sources
• 4FGL: see Fermi
• 4LGSF: see European Southern Observatory Very Large Telescope
• 4MOST: spectrograph in development for VISTA telescope
• 4MOST: see VISTA
• 4U: see Uhuru
• 4XMM: see XMM-Newton
• 4XMM-DR13: see XMM-Newton
• 5-dimensional warped geometry theory (Randall-Sundrum model): particular 5-dimensional cosmological model
• 50000 Quaoar
• Kuiper Belt: further part of solar system beyond Neptune
• 51 Eri b (51 Eridani b): Jupiter-like planet discovered in 2014
• 51 Eridani: see 51 Eridani b
• 51 Eridani b: Jupiter-like planet discovered in 2014
• 51 Peg b (51 Pegasi b): first exoplanet found orbiting a main sequence star
• 51 Pegasi: see 51 Pegasi b
• 51 Pegasi: see extra-solar planet
• 51 Pegasi b: first exoplanet found orbiting a main sequence star
• 53 Persei
• slowly-pulsating B-star: B-star with pulsation periods of more than half a day
• 53 Persei variable (slowly-pulsating B-star): B-star with pulsation periods of more than half a day
• 5335 Damocles: see damocloid
• 55 Cancri A: see 55 Cancri e
• 55 Cancri e: super-Earth orbiting a Sun-like star
• 55 Cnc A: see 55 Cancri e
• 55 Cnc e (55 Cancri e): super-Earth orbiting a Sun-like star
• 5535 Annefrank
• Stardust: space mission that collected and returned comet coma dust
• 55565 2002AW₁₉₇
• Kuiper Belt: further part of solar system beyond Neptune
• 55636 2002 TX₃₀₀
• Kuiper Belt: further part of solar system beyond Neptune
• 55637 UX₂₅
• Kuiper Belt: further part of solar system beyond Neptune
• 5C: see Cambridge Catalog of Radio Sources
• 60-inch Hale Telescope
• coudé focus telescope: type of Nasmyth telescope with additional mirrors
• 60-inch telescope: see Mount Wilson Observatory
• 612911 2004 X_R190
• trans-Neptune object: minor planet beyond Neptune
• 67P (67P/Churyumov-Gerasimenko): comet visited by Rosetta space mission
  • CAESAR: planned space mission to return a sample of a comet
  • Rosetta: space probe that visited a comet
• 67P/C-G (67P/Churyumov-Gerasimenko): comet visited by Rosetta space mission
  • CAESAR: planned space mission to return a sample of a comet
  • Rosetta: space probe that visited a comet
• 67P/Churyumov-Gerasimenko: comet visited by Rosetta space mission
  • CAESAR: planned space mission to return a sample of a comet
  • Rosetta: space probe that visited a comet
• 6C: see Cambridge Catalog of Radio Sources
• 6dF: see UK Schmidt Telescope
  • 6dF Galaxy Survey: UKST survey of galaxies in the southern sky
• 6dF Galaxy Survey: UKST survey of galaxies in the southern sky
• 6dFGS (6dF Galaxy Survey): UKST survey of galaxies in the southern sky
• 775 AD event: apparent solar eruption, based upon tree-ring evidence
• 7C: see Cambridge Catalog of Radio Sources
• 8 pc: survey of stars within 8 parsecs, using coronagraph
• 800 angstrom feature: see reddening
• 84522 2002 TC₃₀₂
• trans-Neptune object: minor planet beyond Neptune
• 87GB (87GB Catalog of Radio Sources): 1980s Green Bank radio survey
• 87GB Catalog of Radio Sources: 1980s Green Bank radio survey
• 8C: see Cambridge Catalog of Radio Sources
• 8pc: see 8 pc
• 90377 Sedna (Sedna): distant solar system planetoid discovered in 2003
  • Kuiper Belt: further part of solar system beyond Neptune
  • trans-Neptune object: minor planet beyond Neptune
• 90482 Orcus
• moon: a planet's natural satellite, such as Earth's
• trans-Neptune object: minor planet beyond Neptune
• 90Prime
• NOAO Source Catalog: catalog compiled from NOAO public data
• 92-cm line
• 21-cm line: hydrogen line useful for determining redshift
• 951 Gaspra
• Galileo: circa 1990s space mission to Jupiter
• 9969 Braille
• Deep Space 1: 1998-2001 mission to fly by asteroid
• 99942 Apophis
• OSIRIS-REx: space mission aiming to return a sample of an asteroid
• 9C: see Cambridge Catalog of Radio Sources
• 9P/Tempel
• Deep Impact: mission to create and observe an impact with a comet