Term Index (R)
Astrophysical terms and names of things beginning with the letter R.
RA
RB
RC
RD
RE
RF
RG
RH
RI
RK
RL
RM
RN
RO
RP
RQ
RR
RS
RT
RU
RV
RW
RX
RY
- R (R band): band of visible light around 6500 angstroms
- R: see Radcliffe Observatory Magellanic Clouds Catalogue
- R: see double star designation
- R: see filter designator
- R: see spectral resolution
- r: see griz photometric system
- r: see ugriz photometric system
- R association: see stellar association
- R band: band of visible light around 6500 angstroms
- R Coronae Borealis variable: see variable star
- R to the 1/4 law (de Vaucouleurs' profile): relation between elliptical galaxy surface brightness and distance from center
- réseau: grid on photographic plate to assist in astrometry
- Rømer (Measuring Oscillations in Nearby Stars): past plan for asteroseismology mission
- Röntgensatellit (ROSAT): 1990s German space X-ray telescope
- r': see ugriz photometric system
- r-process: synthesis of elements through neutron capture faster than beta decay
- r0: see seeing
- R200: see cluster radius
- R200c: see cluster radius
- R200m: see cluster radius
- R500: see cluster radius
- R500c: see cluster radius
- R4He: see Lyman series
- RD: see Lyman series
- Re (effective radius): radius of a galaxy within which 1/2 the light is emitted
- rg: see Schwarzschild radius
- RH (Holmberg radius): a measure of size of galaxy based on surface brightness
- RH (Rydberg constant): constant used in calculating atomic Hydrogen lines
- RHO (Holmberg radius): a measure of size of galaxy based on surface brightness
- rL (Laplace radius): a radius for a stable orbit of a satellite around a planet
- Rm: see Reynolds number
- RS (Schwarzschild radius): radius of a black hole's event horizon
- Rsp: see cluster radius
- RA (right ascension): direction coordinate along celestial equator
- RA: see Mars Polar Lander
- Ra (Rayleigh number): measure reflecting a fluid system's propensity to convection
- Raab: see rare designator prefixes
- RAC: see Mars Polar Lander
- RAC: see Phoenix
- RAD: see Mars Science Laboratory
- rad (radian): angle/arc measurement equivalent to 180/π degrees
- radar: probe based on reflecting radio waves
- Radcliffe Magellanic Clouds (Radcliffe Observatory Magellanic Clouds Catalogue): catalog of stars in
- Radcliffe Observatory
- Radcliffe Observatory Magellanic Clouds Catalogue: catalog of stars in
- Radcliffe wave: wave-shaped string of molecular clouds
- RADEX: radiative transfer code
- radial: see torus coordinates
- radial drift: inward drift of objects within a protoplanetary disk
- radial epicyclic frequency: see epicyclic frequency
- radial mixing: tendency of disk galaxy stars to change their orbital radius
- radial mode: see asteroseismology
- radial motion (radial velocity): component of velocity toward or away from observer
- radial orbit migration (radial mixing): tendency of disk galaxy stars to change their orbital radius
- radial orbit mixing (radial mixing): tendency of disk galaxy stars to change their orbital radius
- radial quantum number
- electron shell: radius-level around an atomic nucleus at which electrons can orbit
- radial velocimetry: see radial velocity
- radial velocity: component of velocity toward or away from observer
- radial velocity method: method of detecting exoplanets and binary companions
- radial velocity method: see extra-solar planet
- radial velocity method: see radial velocity
- EXOFAST: code to match model parameters with exoplanet observation data
- minimum mass: measured bound on the mass of an exoplanet
- telluric line: absorption line in ground observation due to Earth atmosphere
- radial velocity observatory: see radial velocity
- radial-drift barrier: the problem that forming planets would drift inward into the star
- radial-drift barrier: see meter size barrier
- barrier: challenging issue regarding planet formation
- radial-orbit instability (radial mixing): tendency of disk galaxy stars to change their orbital radius
- radian: angle/arc measurement equivalent to 180/π degrees
- radian: see arcsecond
- radiance: measure of EMR to/from a solid angle through an area
- radiance (intensity): power reaching a surface from a specific source
- radiant: see meteoroid
- radiant exposure: see flux
- radiant flux: measure of brightness
- radiant flux density (flux density): measure of the strength of a radio signal
- radiated excitation: see atomic excitation
- radiation (electromagnetic radiation): radiation such as light, radio, X-rays
- radiation: see radioactivity
- electroweak: single conception including both electromagnetic and weak forces
- radiation belt: regions of energetic charged particles surrounding a planet
- radiation belt: see Van Allen belts
- Jupiter: largest planet in the solar system
- radiation chemistry: see radiolysis
- radiation detector
- radiation driven implosion: see star formation
- radiation era: early-universe era when radiation pressure dominated
- radiation era (radiation era): early-universe era when radiation pressure dominated
- radiation flux (radiative flux): power passing through a unit area
- radiation hydrodynamics: hydrodynamics plus the effects of EMR
- radiation hydrodynamics: see hydrodynamics
- HARM²: technique for parallelizing computations of radiation with hydrodynamics
- radiation magnetohydrodynamics: see hydrodynamics
- radiation pattern (antenna pattern): a radio telescope's pattern of directional sensitivity
- radiation pressure: the pressure exerted by electromagnetic radiation
- radiation zone: region of a star transmitting energy through radiative diffusion
- radiation-dominated era (radiation era): early-universe era when radiation pressure dominated
- radiative cooling timescale: see timescale
- radiative diffusion: see radiation zone
- radiative equilibrium
- radiative flux: power passing through a unit area
- radiative flux density (radiative flux): power passing through a unit area
- radiative forcing: difference between a planet's incoming and outgoing radiation
- radiative lifetime
- radiative region (radiation zone): region of a star transmitting energy through radiative diffusion
- radiative timescale: see timescale
- radiative transfer: energy transfer in the form of electromagnetic radiation
- radiative transfer code: computer model of a gas's radiative transfer
- radiative transfer equation (equation of radiative transfer): equation describing energy transfer by EMR
- radiative transfer model: models of radiative transfer, often computerized
- radiative transport equation (equation of radiative transfer): equation describing energy transfer by EMR
- radiative zone (radiation zone): region of a star transmitting energy through radiative diffusion
- radiative-convective boundary: see convection zone
- radiative-convective climate model (one dimensional climate model): atmospheric model ignoring all horizontal motion
- radical
- hydroxyl: one hydrogen atom and one oxygen atom bound together
- radio: electromagnetic radiation, frequency 3 kHz to 300 GHz
- 1 Jansky Empty Field Survey: 1980s survey to find optical identifications for weak radio sources
- 1.3-mm observation: observation frequency useful for detecting dust
- 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 48: radio galaxy/quasar
- 3C 9: first quasar discovered
- 87GB Catalog of Radio Sources: 1980s Green Bank radio survey
- Africa Millimetre Telescope: planned 15 m radio telescope array in Namibia
- Algonquin Radio Observatory: 46 meter radio telescope
- Allen Telescope Array: array of radio telescopes in northern California for SETI
- antenna pattern: a radio telescope's pattern of directional sensitivity
- Arecibo Observatory: former large 305 m radio telescope in Puerto Rico
- Arecibo Occultation Survey: 1960s radio survey using occultations by the Moon
- ASPECS: millimeter survey of HUDF
- ASTRON: Netherlands radio astronomy research organization
- Astronomical Image Processing System: software for processing radio astronomy data
- Atacama Large Millimeter Array: large millimeter telescope array in Chile
- Australia Telescope Compact Array: radio telescope in eastern Australia
- Australia Telescope Large Area Survey: radio survey of two survey fields
- Australian Square Kilometre Array Pathfinder: radio telescope array of 36 12-meter dishes
- back end instrument: instruments of a telescope that process or combine signals
- Badgerys Creek Interferometer 101-MHz Survey: early 1950s survey of southern-hemisphere radio sources
- bandpass filter: device to filter away all but a band of frequencies
- beam: portion of a sky that a radio telescope is viewing
- Becker, White, and Edwards Catalog: 1990s radio catalog from a Green Bank 300ft Telescope survey
- BINGO: future radio telescope for mapping distant neutral hydrogen
- Bologna Survey of Radio Sources: 1970s-1980s radio survey
- Cambridge Catalog of Radio Sources: series of catalogs of northern hemisphere sources
- Canadian Hydrogen Intensity Mapping Experiment: radio telescope mapping distant neutral hydrogen
- CASA: software package for radio interferometry image generation
- Centaurus A: nearby radio galaxy
- Chinese Pulsar Timing Array: group of pulsars timed by FAST
- COMAP: high frequency radio telescope to map CO
- Combined Array for Research in Millimeter-wave Astronomy: former array of radio telescopes in eastern California
- commensal mode: telescope usage that accomplishes multiple observations simultaneously
- confusion limit: limit on telescope imaging due to too many sources in the same region
- Cosmic Anisotropy Telescope: 1990s interferometer to measure CMB variations
- Cosmic Lens All-sky Survey: 1990s/2000s radio survey aimed at gravitational lensing
- CRATES: catalog of 8.4 GHz data on radio sources
- Cygnus A: early-discovered radio galaxy showing a quasar
- cylindrical telescope: telescope with cylindrical reflectors
- dirty image: image that includes the distortions of the beam and sampling
- dispersion measure: to what degree an EMR signal's lower frequencies are delayed
- Dominion Observatory 10.03 MHz Source Catalog: 1960s survey of northern-hemisphere radio sources
- Dominion Observatory 1420 MHz Source Catalog: 1960s survey of northern-hemisphere radio sources
- Dominion Radio Astrophysical Observatory: radio observatory in British Columbia, Canada
- downconverter: device that reduces the frequency of a signal
- DSA-2000: array plan to detect radio transients
- Dwingeloo Obscured Galaxy Survey: radio survey of ZOA for 21-cm lines indicating galaxies
- Earth rotation synthesis: using the Earth's rotation to observe with various interferometry baselines
- Earth-sized VLBI: ground-based VLBI with near-maximal baseline
- EBEX: balloon-based CMB polarization survey
- EDGES: survey aiming at highly-redshifted 21-cm detection
- Effelsberg 100-m Radio Telescope: German large single-dish radio telescope
- electromagnetic spectrum: spectrum of EMR
- European Pulsar Timing Array: European collaboration of radio telescopes
- European VLBI Network: consortium of radio telescopes to coordinate VLBI efforts
- Event Horizon Telescope: growing VLBI network
- extremely low frequency: electromagnetic radiation, frequency 3 Hz to 30 Hz
- Fanaroff-Riley classification: a classification of the radio characteristics of radio sources
- FAST: Arecibo-like 500 m telescope in China
- Fast Fourier Transform Telescope: proposed all-digital telescope with synthetic aperture
- Fast On-orbit Rapit Recording of Transient Events: satellite viewing radio and optical transients on Earth
- fast radio burst: astronomical high energy radio pulses of a few milliseconds
- filter bank: set of filters to simultaneously produce radio data within bands
- FIRST: 1990s radio survey
- Five College Radio Astronomical Observatory: former observatory near Springfield MA
- flux density: measure of the strength of a radio signal
- focal plane array: array of receivers at the focus of a radio telescope
- Fourth Cambridge Catalog of Radio Sources: 1960s catalog of northern hemisphere 178 MHz sources
- frequency modulation: changing the frequency of a signal's carrier
- front end instrument: instruments of a telescope that detect and encode the signal
- G1.9+0.3: recent supernova remnant in Sagittarius
- Galactic Emission Mapping: radio sky survey
- GCRT: galactic center radio transient
- Giant Metrewave Radio Telescope: large radio interferometer in India
- GLEAM: MWA radio survey of the southern sky
- Gould's Belt Distances Survey: survey of parallax distances to Gould's Belt YSOs
- Green Bank 140 Foot Telescope: West Virginia radio telescope
- Green Bank 300ft Telescope: former large radio telescope at Green Bank
- Green Bank 6-cm Radio Source Catalog: catalog of from 1980s northern-hemisphere radio survey
- Green Bank Telescope: West Virginia large radio telescope
- Greenland Telescope: 12 m radio telescope in Greenland
- GUPPI: radio-telescope back-end aimed at processing pulsar data
- HALCA: Japanese space radio telescope operating 1997-2005
- HERA: low frequency radio telescope
- HI Jodrell All-Sky Survey: northern-hemisphere HI survey carried out in late 90s/early 2000s
- High Time Resolution Universe Survey: c2010 search for pulsars and radio transients
- HIPASS: HI survey carried out 1997 to 2002
- HIRAX: radio telescope array for 21-cm surveying
- Hydrogen Accretion in Local Galaxies Survey: radio survey looking for HI in galaxy halos
- Indian Pulsar Timing Array: group of pulsars timed by the GMRT
- Institut de radioastronomie millimétrique: organized radio astronomy collaboration between France, Germany, and Spain
- Interplanetary Scintillation Array: UK radio telescope that first detected pulsars
- ionosphere: layers of Earth atmosphere with significant ions
- IRAM 30m Telescope: millimeter-range radio telescope in Sierra Nevada, Spain
- ITU: international body coordinating communications technology
- jansky: unit of measurement of spectral flux density
- Jodrell Bank Observatory: radio observatory in England
- Long Baseline Array: radio interferometer using Australian telescopes
- Long Wavelength Array: radio telescope in New Mexico
- low frequency radio astronomy: astronomy using the lower end of the radio spectrum
- Low-frequency Array: low frequency radio telescope
- LSPE-STRIP: CMB survey telescope in Canary Islands
- LSPE-SWIPE: plan for a balloon-based CMB polarization survey
- Mark II: 38 m radio telescope in England
- Max Planck Institute for Radio Astronomy: Bonn research institute
- MeerKAT: new radio telescope in South Africa
- MeerKAT Pulsar Timing Array: group of pulsars timed by MeerKAT
- MeerKLASS: 21-cm-line survey using MeerKAT
- Meier paradox: mysterious decline in number of radio galaxy jets
- MERLIN: VLBI array spread across England
- microwave: electromagnetic radiation, frequency 300 MHz to 300 GHz
- MIGHTEE: radio survey of four established deep fields
- millimeter astronomy: observation and analysis at wavelengths on the order of a millimeter
- minkasi: code for processing MUSTANG-2 data
- MOJAVE: program to monitor AGN jet radio brightness and polarization
- Molonglo Reference Catalog: 1981 catalog of mostly southern hemisphere radio sources
- Mopra Telescope: Australian 22 m radio telescope
- MOST: radio telescope in New South Wales
- MSH Catalog: 1950s catalog of radio sources from a Mills Cross survey
- Mullard Radio Astronomy Observatory: radio observatory near Cambridge, UK
- multichroic feedhorn array: radio array with sensors for two or more bands
- Murchison Widefield Array: low frequency radio telescope
- MUSTANG: bolometer array on the Green Bank Telescope
- Nançay Radio Telescope: large radio telescope in France
- NANTEN2: millimeter telescope in Chile
- National Radio Astronomy Observatory: US radio astronomy organization
- Next Generation Very Large Array: planned radio telescope array as a follow-on to ALMA and the Jansky VLA
- Northern Extended Millimeter Array: large radio telescope array under construction in Europe
- NRAO Catalog: 1960s follow-up to Cambridge radio surveys
- odd radio circle: extragalactic ring-shaped radio source noticed in 2020
- Ohio Radio Survey: 1960s radio survey by Ohio State University
- Ooty Radio Telescope: cylindrical radio telescope in India
- outrigger: radio receiver some distance from main receiver for direction determination
- OVRO-LWA: radio telescope in California
- Owens Valley Radio Observatory: group of radio telescopes in California near the VLBA
- PALFA: Arecibo search for pulsars
- PAPER: radio interferometer for 21-cm measurement
- Parkes Catalog: catalog of from 1960s-1990 of radio sources in southern hemisphere
- Parkes Multibeam Pulsar Survey: late 1990s radio survey in search of pulsars
- Parkes Observatory: Australian observatory with large single-dish radio telescope
- Parkes Pulsar Timing Array: group of pulsars timed by Parkes Observatory
- Parkes-MIT-NRAO Surveys: 1990 southern-hemisphere radio surveys
- phased array: method of using a set of antennas directionally
- plasma frequency: frequency of electron plasma oscillation
- pulsar timing array: cooperating set of pulsar timing observatories
- PUPPI: Arecibo radio-telescope instrument aimed at observing pulsars
- QMAP: mid 1990s balloon-based CMB survey
- quad-ridge flared horn: type of horn that can be incorporated in radio telescope feeds
- Queen's University Radio Observatory: early radio astronomy facility near Kingston, Ontario
- radar: probe based on reflecting radio waves
- radio astronomy: astronomy observation and analysis of radio EMR
- Radio Camera Initiative: initiative to design radio interferometry correlators
- radio frequency interference: transmissions in a frequency band under observation
- radio galaxy: a galaxy emitting a lot of radio
- Radio Galaxy Zoo: crowd-sourced classification of radio galaxies
- radio halo: type of diffuse radio source at the center of a galaxy cluster
- radio phoenix: region of galaxy cluster from which radio is emitted a subsequent time
- radio relics: clouds from past galaxy emitting radio synchrotron radiation
- radio science: radar and other methods of using radio to probe planets and moons
- radio source: astronomical object producing observable radio
- radio source counts: using radio source population characteristics to determine curvature
- radio star: star emitting much radio
- radio supernova: supernova that includes a detectable radio emission
- radio telescope: telescope that operates in the radio frequency range of EMR
- radiometer equation: shows how long to observe a radio source
- RASS/Green Bank Catalog: combined list of radio galaxies from Rosat and Green Bank surveys
- RATAN-600: ring-shaped radio telescope in Russia
- RELIKT-1: instrument on 1980s Soviet satellite to view the CMB
- RMS astronomy: collective term for radio, millimeter, and submillimeter
- rotating radio transient: radio bursts repeating sporadically
- SARAS: survey aiming at highly-redshifted 21-cm detection
- Sardinia Radio Telescope: Italian large single-dish radio telescope
- Society of Amateur Radio Astronomers: US organization
- Spektr-R: 10 m space radio telescope
- Square Kilometre Array: planned radio telescope with square-kilometer collecting area
- STARE: array of radio telescopes monitoring radio transients
- Strong Source Surveys: series of 1970s/1980s 5 GHz surveys
- Submillimeter Array: radio interferometer in Hawaii
- submillimeter astronomy: astronomy observation and analysis of borderline infrared EMR
- super low frequency: electromagnetic radiation, frequency 30 Hz to 300 Hz
- Swedish-ESO Submillimetre Telescope: former 15 m radio telescope array in Chile
- synthetic aperture radar: method of using moving radar with a stationary target
- Texas Survey of Radio Sources at 365 MHz: 1970s/1980s radio survey made with the Texas Interferometer
- Third Cambridge Catalogue of Radio Sources: 1959 catalog of northern hemisphere 159-MHz sources
- Tianlai Project: 21-cm line intensity mapping project
- TopHat: 2001 balloon -based CMB survey
- tremendously low frequency: presumably electromagnetic radiation, frequency below 3 Hz
- TXS 0506+056: blazar that is a neutrino source
- ultra low frequency: electromagnetic radiation, frequency 300 Hz to 3 kHz
- USS Sources: catalog of sources with steep spectral index
- UTMOST: telescope aiming to detect radio transients
- VERA: VLBI project to map the Milky Way
- Very Large Array: radio telescope in New Mexico
- Very Long Baseline Array: radio interferometer stretching 8000 km
- very low frequency: electromagnetic radiation, frequency 3-30 kHz
- Very Small Array: radio interferometer in Canary Islands
- very-long-baseline interferometry: interferometry based upon storing timing data at each telescope
- VLASS: ongoing all-sky radio survey
- Westerbork Synthesis Radio Telescope: radio telescope array of 14 dishes in Netherlands
- Westerhout Radio Survey: 1950s radio survey of the galactic plane
- Yuan-Tseh Lee Array: microwave interferometer in Hawaii
- Radio Astronomical Telescope Academy Nauk 600 (RATAN-600): ring-shaped radio telescope in Russia
- radio astronomy: astronomy observation and analysis of radio EMR
- integration time: time spent acquiring a signal
- radio: electromagnetic radiation, frequency 3 kHz to 300 GHz
- Radio Camera Initiative: initiative to design radio interferometry correlators
- radio counterpart: see counterpart
- radio frequency
- radio frequency interference: transmissions in a frequency band under observation
- radio galaxy: a galaxy emitting a lot of radio
- Radio Galaxy Zoo: crowd-sourced classification of radio galaxies
- radio halo: type of diffuse radio source at the center of a galaxy cluster
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- radio interferometer: see interferometer
- radio interferometry: see interferometry
- radio jet: see jet
- radio loud
- blazar: very compact variable quasar
- radio loud quasar: see quasar
- radio millimeter submillimeter wavelength astronomy (RMS astronomy): collective term for radio, millimeter, and submillimeter
- Radio Optical Reference Frame: 1994 celestial reference frame based on 436 sources
- radio phoenix: region of galaxy cluster from which radio is emitted a subsequent time
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- radio quiet quasar: see quasar
- radio quiet zone: see Green Bank Observatory
- dark sky: sky with limited light pollution
- radio relic
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- radio relics: clouds from past galaxy emitting radio synchrotron radiation
- radio science: radar and other methods of using radio to probe planets and moons
- radio source: astronomical object producing observable radio
- source: astronomical object producing some observed signal
- radio source counts: using radio source population characteristics to determine curvature
- radio source star (radio star): star emitting much radio
- radio spectral index: see spectral index
- radio star: star emitting much radio
- radio supernova: supernova that includes a detectable radio emission
- radio telescope: telescope that operates in the radio frequency range of EMR
- radio transient: see transient
- radio transients
- radio waves (radio): electromagnetic radiation, frequency 3 kHz to 300 GHz
- radio window: see atmospheric window
- radio YSO: see young stellar object
- radio-loud: see radio galaxy
- radio-loud blazar: see radio galaxy
- radio-loud quasar: see radio galaxy
- radio-quiet: see radio galaxy
- radioactive dating: determining the age of a substance that has a radioactive component
- radioactive decay: changes in atomic nuclei that happen over time
- radioactive decay timescale: see radioactive decay
- radioactive heating: a source of heat of some planets and moons
- radioactive isotope: see isotope
- radioactivity: an unstable nucleus's tendency to change through emission of particles
- radioactivity: see radioactive decay
- RadioAstron
- radiochemistry: see radiolysis
- radiogenic heating (radioactive heating): a source of heat of some planets and moons
- Radioisotope Heat Unit: see MMRTG
- Radioisotope Thermoelectric Generator: type of spacecraft power source for instruments
- radiolysis: similar to photodissociation from higher energy photons
- radiolytic chemistry: see radiolysis
- radiometer: device for measuring radiant flux
- radiometer equation: shows how long to observe a radio source
- radiometric dating (radioactive dating): determining the age of a substance that has a radioactive component
- radiometric noise: see noise temperature
- radiometry: see radiometer
- radius
- radius gap (Fulton gap): planets with radius 1.5 to 2 Earth radii are rare
- radius of stability: see circumbinary planet
- radius valley (Fulton gap): planets with radius 1.5 to 2 Earth radii are rare
- Radon transform: see tomography
- RAFGL: see AFGL Four Color Infrared Sky Survey
- Ralph: see New Horizons
- ram pressure: pressure on a body moving through a fluid
- ram-pressure stripping: see ram pressure
- RAMBO: proposed astronomical objects comprising dark matter
- ramp: see filter designator
- RAMSES: hydrodynamic simulation system
- Randall-Sundrum braneworld (Randall-Sundrum model): particular 5-dimensional cosmological model
- Randall-Sundrum model: particular 5-dimensional cosmological model
- random error: see systematic error
- random forest: algorithmic method of developing decision trees
- random walk: movement with random turns
- radiation zone: region of a star transmitting energy through radiative diffusion
- Rapid Approximate Spectral Calculations for All (RASCALL): efficient code to locate suspected molecular lines
- Rapid Eye Mount Telescope: quick-action robotic telescope at La Silla Observatory
- rapid neutron-capture process (r-process): synthesis of elements through neutron capture faster than beta decay
- s-process: synthesis of elements through neutron capture and beta decay
- rapid proton-capture process (rp-process): synthesis of elements through repeated proton capture
- rapid quenching: see quenched galaxy
- Rapid Telescopes For Optical Response (RAPTOR): automated array of telescopes to uncover and track transients
- rapid weathering: see weathering
- rapidly oscillating Ap star: see Ap star
- RAPTOR: automated array of telescopes to uncover and track transients
- rare designator prefixes: designator prefixes generally used for only a few objects
- rare earth element: see lanthanide
- RAS (Royal Astronomy Society): UK society supporting and promoting astronomy
- RAS JobList: directory of astrophysics jobs
- RASC (Royal Astronomy Society of Canada): Canadian society supporting and promoting astronomy
- RASCALL: efficient code to locate suspected molecular lines
- RASCALL database: see RASCALL
- RASS: see ROSAT
- RASS/Green Bank Catalog: combined list of radio galaxies from Rosat and Green Bank surveys
- RASSGB (RASS/Green Bank Catalog): combined list of radio galaxies from Rosat and Green Bank surveys
- RAT: see Mars Exploration Rover
- RAT: see rare designator prefixes
- Rat deutscher Sternwarten (Council of German Observatories): German astronomy research council
- RATAN-600: ring-shaped radio telescope in Russia
- ratio
- ratio of total to selective visual extinction: see reddening
- ray tracing
- HARM²: technique for parallelizing computations of radiation with hydrodynamics
- Rayleigh criteria
- parallax: angle due to different lines of sight
- Rayleigh criterion: see angular resolution
- apodization: improving telescope images by manipulating diffraction
- PSF fitting: untangling airy disks to gain effective resolution
- Rayleigh distribution: see Maxwell-Boltzmann distribution
- Rayleigh Jeans Law
- Rayleigh number: measure reflecting a fluid system's propensity to convection
- Rayleigh scattering: wave scattering by particles smaller than the wavelength
- Rayleigh-Jeans approximation (Rayleigh-Jeans law): yields approximation of black-body curve useful at low frequencies
- Rayleigh-Jeans law: yields approximation of black-body curve useful at low frequencies
- Rayleigh-Jeans limit (Rayleigh-Jeans law): yields approximation of black-body curve useful at low frequencies
- Rayleigh-Jeans limit: see Rayleigh-Jeans law
- Rayleigh-Jeans regime: see Rayleigh-Jeans law
- Rayleigh-Jeans region: see Rayleigh-Jeans law
- Rayleigh-Jeans tail: see Rayleigh-Jeans law
- Rayleigh-Taylor instability (RT instability): result of lighter fluid pushing a heavier fluid
- RB: see rare designator prefixes
- RBS (Rosat Bright Survey): list of bright X-ray sources from ROSAT observations
- RC (Reference Catalogue of Bright Galaxies): series of catalogs of nearby galaxies
- RC (Ritchey-Chrétien telescope): type of two-mirror reflector telescope
- RC (red clump): like horizontal branch but at one temperature
- RC: see rare designator prefixes
- RC star: see red clump
- RC1 (Reference Catalogue of Bright Galaxies): series of catalogs of nearby galaxies
- RC2: see Reference Catalogue of Bright Galaxies
- RC3: see Reference Catalogue of Bright Galaxies
- RCB: see convection zone
- RCB: see variable star
- RCG (Abell Catalog): galaxy cluster catalog assembled over 1950s-1980s
- RCG: see red clump
- RCI (Radio Camera Initiative): initiative to design radio interferometry correlators
- RCS: see rare designator prefixes
- RCT (Ritchey-Chrétien telescope): type of two-mirror reflector telescope
- RCT: see Kitt Peak National Observatory
- RCW: see rare designator prefixes
- RCW 86: see SN 185
- RD: see dropout
- RDCS: see ROSAT
- RDI (reference star differential imaging): identifying speckles by comparing star-images
- RDI: see star formation
- RDM (repulsive dark matter): concept of dark matter that resists extreme dark-matter density
- RDRS: see Magellan
- RDS (Council of German Observatories): German astronomy research council
- RDS: see ROSAT
- RE: see ROSAT
- Re (Reynolds number): measure reflecting a fluid system's propensity to turbulence
- Re-simulated Halo Sample for Statistics Observable-mass Distribution Study (RHAPSODY): simulation of galaxy cluster dark-matter halos
- REACH: see Subaru Telescope
- REACT
- reaction
- reaction wheel
- K2: second Kepler mission that worked around failed equipment
- Kepler Telescope: space telescope that watched stars for exoplanets
- real image: image that would show on a screen placed at its location
- real number
- complex number: type of number that can be the square root of a negative number
- real part: see complex number
- REASON: see Europa Clipper
- REBELS: survey of star-forming galaxies during the reionization
- REBOUND: code to carry out N-body simulations
- recessional velocity: see redshift
- recoil
- GW detection: observed gravitational wave signal recognizable as an astronomical event
- recombination: time when the universe's ionized hydrogen atoms neutralized
- reconnection (magnetic reconnection): change in magnetic topology within a fluid
- reconnection sheet: see current sheet
- RECONS: consortium for research on stars near the Sun
- recurrent nova: see nova
- recycled pulsar: see millisecond pulsar
- red: see globular cluster
- R band: band of visible light around 6500 angstroms
- red and dead: description of a galaxy with old stars and no star formation
- red clump: like horizontal branch but at one temperature
- horizontal branch: a second "giant" stage in the evolution of some main sequence stars
- red clump giant: see red clump
- red clump star: see red clump
- horizontal branch: a second "giant" stage in the evolution of some main sequence stars
- Red de Infraestructuras de Astronomie: Spanish astronomy research organization
- red dropout galaxy: see dropout
- red dwarf: small, cool main-sequence star
- red dwarfs
- L-type star: spectral type of star cooler than an M-type star
- M dwarf: small, cool main-sequence star in stellar class M
- red edge (vegetation red edge): wavelength cut-off point in the reflectivity of typical plants
- red galaxy: see galaxy main sequence
- galaxy: gravitationally-bound group of stars
- red giant: very bright red star
- red kilonova model: see kilonova
- red noise: noise tending toward lower frequencies
- red quasar: see quasar
- red shift
- Doppler shift: wave frequency difference due to relative velocity difference with source
- Red Spot
- red straggler: see turn-off point
- red supergiant: see supergiant
- red supergiant cluster: stellar cluster with multiple red supergiants
- red-giant branch: the first red-giant phase of post-main-sequence stellar evolution
- reddening: red appearance of astronomical objects because blue light is attenuated by dust
- 2175 angstrom feature: prominent absorption feature in ISM
- extinction: the absence of any radiation from an astronomical object because all is absorbed or scattered
- redox: see reducing atmosphere
- redox potential (reduction potential): measure of a chemical species' tendency to acquire electrons
- redshift: change to longer wavelengths due to Doppler effects
- Redshift Evolution and Formation in Extragalactic Systems (REFINE): catalog of high-redshift galaxies
- redshift parameter (redshift): change to longer wavelengths due to Doppler effects
- redshift space: concept of space using redshift as the radial dimension
- redshift space distortion: see redshift space
- redshift survey: survey of the universe aiming at three dimensions
- redshift space: concept of space using redshift as the radial dimension
- redshift-angular size relation: how observed size of an object depends on its redshift
- redshift-magnitude relation: how apparent magnitude depends on redshift
- reduced Compton wavelength: see Compton wavelength
- reduced mass: the reciprocal of the sum of the reciprocals of the masses of two objects
- reduced Planck constant: see Planck constant
- reducing agent: see reducing atmosphere
- reducing atmosphere: atmosphere lacking oxygen and other oxidizers
- reduction: see reducing atmosphere
- reduction potential: measure of a chemical species' tendency to acquire electrons
- reference
- bibcode: reference code for a journal article
- J designator: designator using equatorial coordinates at year 2000
- phone number: colloquial expression for coordinates
- Reference Catalogue of Bright Galaxies: series of catalogs of nearby galaxies
- reference direction: see orbital element
- reference frame (celestial reference frame): frame of reference associated with a catalog of stars or quasars
- reference plane
- reference star
- reference star differential imaging: identifying speckles by comparing star-images
- REFINE: catalog of high-redshift galaxies
- refined Bouguer correction: see Bouguer anomaly
- refined Bouguer reduction: see Bouguer anomaly
- reflecting telescope (reflector telescope): telescope using mirrors rather than lenses to magnify
- reflection
- earthshine: reflected and emitted electromagnetic radiation from Earth
- reflection nebula: nebula made visible by light it scatters from nearby stars
- reflection spectroscopy
- reflective grating: see grating
- reflector (reflector telescope): telescope using mirrors rather than lenses to magnify
- reflector telescope: telescope using mirrors rather than lenses to magnify
- refracting telescope: telescope using lenses rather than mirrors to magnify
- refraction: redirection of light passing from one medium to another
- refractive index: measure of how much a material slows down light
- refractive interstellar scintillation: refraction of star light by the ISM
- refractive scintillation (refractive interstellar scintillation): refraction of star light by the ISM
- refractor (refracting telescope): telescope using lenses rather than mirrors to magnify
- refractory (refractory material): material with high condensation temperature
- refractory compound: see refractory material
- refractory element: see refractory material
- refractory inclusion: see refractory material
- refractory material: material with high condensation temperature
- region of instability (instability region): region around an object where orbits cannot persist
- regolith: loose solid material covering a planet's solid rock
- regolith scale: see regolith
- regular moon: see irregular moon
- regular perturbation problem: see perturbation theory
- regular satellite: see irregular moon
- reheating: theorized increase in temperature after cosmological inflation
- reionization (epoch of reionization): time when the universe's neutral hydrogen atoms ionized
- reionization by oligarchs: see epoch of reionization
- reionization epoch (epoch of reionization): time when the universe's neutral hydrogen atoms ionized
- Reionization Era Bright Emission Line Survey (REBELS): survey of star-forming galaxies during the reionization
- Reipurth: see rare designator prefixes
- Reissner-Nordström black hole: see black hole model
- Reissner-Nordström metric: see metric
- Reissner-Nordström object: see black hole model
- relation
- relative astrometry: see astrometry
- relative atomic mass: see element
- relative humidity: see humidity
- relative photometry: see photometry
- relativistic aberration: see aberration
- relativistic astrophysics: physics applicable to cosmology and strong field gravity
- relativistic beaming: directional relativistic effect on light from relativistic speeds
- relativistic cosmology: see cosmology
- relativistic Doppler effect: see Doppler shift
- relativistic effect: a substantial fraction of the speed of light
- relativistic energy: energy of an object including relativistic effects
- relativistic hydrodynamics: see hydrodynamics
- relativistic invariance: quantity that remains the same regardless of frame of reference
- relativistic jet: see jet
- relativistic Limber equation: see Limber approximation
- relativistic magnetohydrodynamics: see hydrodynamics
- relativistic mass: see mass
- relativistic mechanics: see mechanics
- relativistic momentum: momentum of an object including relativistic effects
- relativistic speed: a substantial fraction of the speed of light
- relativistic Sunyaev-Zel'dovich effect: see Sunyaev-Zel'dovich effect
- relativistic velocity: see relativistic speed
- relativity: physics models accommodating the constancy of the speed of light
- relaxation: see relaxation time
- relaxation time: time associated with exponential falloff
- relaxation time: see e-folding time
- Stokes number: measure of a particle's tendency to follow the flow of a fluid
- timescale: general length of time something takes
- relic: particles left over from the events of the early universe
- freeze-out: particles existing long-term after a decoupling
- relic abundance: see Big Bang nucleosynthesis
- relic abundance: see relic
- relic neutrinos (cosmic neutrino background): low-energy neutrinos left over from early universe
- RELIKT-1: instrument on 1980s Soviet satellite to view the CMB
- REM (Rapid Eye Mount Telescope): quick-action robotic telescope at La Silla Observatory
- Rem: see Reynolds number
- REMIR: see Rapid Eye Mount Telescope
- remnant (stellar remnant): leftovers from a mainstream star
- remnant (supernova remnant): nebula of debris resulting from a supernova
- REMS: see Mars Science Laboratory
- Renson: see rare designator prefixes
- repulsive dark matter: concept of dark matter that resists extreme dark-matter density
- resampling
- Research Consortium On Nearby Stars (RECONS): consortium for research on stars near the Sun
- Research Experience for Undergraduates: NSF funding program
- Research Foundation - Flanders: Belgian research council
- Research Opportunities in Space and Earth Science: NASA program
- Research School of Astronomy and Astrophysics: Australian National University astrophysics school
- resistance: see siemens
- resistance heating (Ohmic heating): heating resulting from an electric current through a material
- resistive MHD: see magnetohydrodynamics
- resistivity: see siemens
- flux freezing: magnetic field lines becoming attached to plasma they pass through
- Reynolds number: measure reflecting a fluid system's propensity to turbulence
- resolution (angular resolution): measure of a telescope's ability to distinguish spatial detail
- resolution (spectral resolution): measure of a spectrograph's ability to resolve features of the spectrum
- resolution convergence: see cosmological zoom simulation
- Resolve: see XRISM
- RESOLVE: galaxy and gas survey limited to 65-100 Mpc
- resolved source (extended source): term for astronomical object covering some area of the sky
- point source: celestial object that focuses to a point or single Airy disk
- Resolved Spectroscopy of a Local Volume (RESOLVE): galaxy and gas survey limited to 65-100 Mpc
- Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics (ROCKE-3D): rocky-planet-oriented general circulation model
- resolving power: see spectral resolution
- resonance
- resonance locking: see tidal migration
- resonant fluorescence: see fluorescence
- resonant frequency: see normal mode
- resonant TNO: see trans-Neptune object
- resonant trans-Neptunian object: see trans-Neptune object
- resonator-bolometer KID: see KID
- rest energy: see relativistic energy
- rest frame: see frame of reference
- rest mass: see mass
- rest wavelength: normal wavelength observed when not moving in relation to the source
- Restore-L (OSAM-1): prototype space robot for servicing satellites
- restricted circular three-body problem: see Jacobi integral
- Reticulum: see rare designator prefixes
- Reticulum II
- retrieval: determining parameters through observation and modeling
- Tau-REx: spectral line retrieval code for exoplanet atmospheres
- retrieval code: see retrieval
- retrograde accreting black hole: see retrograde accretion
- retrograde accretion: accretion disk spinning in opposite direction to the body
- retrograde accretion disk: see retrograde accretion
- retrograde hot Jupiter: large hot planet orbiting opposite the expected direction
- retrograde motion: see retrograde orbit
- epicycle: small circular motion around a large circular motion
- retrograde orbit: orbit opposite the usual direction
- retrograde rotation: see retrograde orbit
- retrograde rotation: see rotation period
- retroreflector
- LARES: satellite to test a general relativity effect
- REU (Research Experience for Undergraduates): NSF funding program
- reverberation mapping: technique for measuring the size of SMBHs
- reverse beta decay: see beta decay
- reversing layer: see Schuster-Schwarzschild model
- review item exchange (RIX): enquiry/answer about some issue regarding a project review
- Revised AFGL: see AFGL Four Color Infrared Sky Survey
- Revised Luyten Half-second Catalog: see Luyten Half-second Catalog
- Revised NGC: see New General Catalogue
- Revised NGC and IC: see New General Catalogue
- Revised Shapley-Ames Catalog: see Shapley-Ames Catalog
- REX: see New Horizons
- Reynolds decomposition: mathematical separation of average and fluctuating parts of a quantity
- Reynolds number: measure reflecting a fluid system's propensity to turbulence
- Reynolds stress
- RF (radiative forcing): difference between a planet's incoming and outgoing radiation
- RF interference (radio frequency interference): transmissions in a frequency band under observation
- RFGC: see rare designator prefixes
- RFI (radio frequency interference): transmissions in a frequency band under observation
- RG (radio galaxy): a galaxy emitting a lot of radio
- RG: see rare designator prefixes
- RGB (RASS/Green Bank Catalog): combined list of radio galaxies from Rosat and Green Bank surveys
- RGB (red-giant branch): the first red-giant phase of post-main-sequence stellar evolution
- RGB phase: see red-giant branch
- RGB star: see red-giant branch
- RGG: see rare designator prefixes
- RGO (Royal Greenwich Observatory): former UK national observatory
- RGS: see XMM-Newton
- RGZ (Radio Galaxy Zoo): crowd-sourced classification of radio galaxies
- RHAPSODY: simulation of galaxy cluster dark-matter halos
- RHAPSODY-C: see RHAPSODY
- RHAPSODY-G: see RHAPSODY
- RHCP: see polarization
- RHD (radiation hydrodynamics): hydrodynamics plus the effects of EMR
- RHD: see hydrodynamics
- HARM²: technique for parallelizing computations of radiation with hydrodynamics
- Rhea: see Saturn
- moon: a planet's natural satellite, such as Earth's
- Rho Cassiopeiae
- Rho Ophiuchi
- Rho Ophiuchi Cloud Complex: nebula that is a nearby star-forming region
- LDN 1689: dense core within the Rho Ophiuchi Cloud Complex
- RHS (Rosat Hard Survey): list of hard X-ray sources from ROSAT observations
- RHT: see Hough transform
- RHU: see MMRTG
- Ri (Richardson number): measure of fluid stability consisting of ratio of buoyancy and shear
- RIA (Red de Infraestructuras de Astronomie): Spanish astronomy research organization
- Richardson number: measure of fluid stability consisting of ratio of buoyancy and shear
- Riddle: see rare designator prefixes
- Ridge A
- Riemann problem: consequence of discontinuities in numerical methods
- Rigel: brightest star in constellation Orion
- Orion: well-known constellation in the northern hemisphere
- right ascension: direction coordinate along celestial equator
- right hand rule
- right-hand circular polarization: see polarization
- Rigil Kentaurus (Alpha Centauri): nearest star system
- RIMAS: see Lowell Discovery Telescope
- RIME: see JUICE
- RIMFAX: see Mars 2020
- ring: see ring system
- ring galaxy: ring-like galaxy, darker in the middle
- ring laser: see Sagnac effect
- ring singularity: see gravitational singularity
- ring system: disk or set of rings orbiting a planet
- disk: rotating disk-shaped object such as disk galaxy or circumstellar disk
- J1407: star eclipsed by a body with a ring system
- Saturn: second largest planet in the solar system
- Uranus: second outer-most solar system planet
- ringdown: see GW detection
- rings
- disk: rotating disk-shaped object such as disk galaxy or circumstellar disk
- ring system: disk or set of rings orbiting a planet
- shepherd moon: small moon affecting outer edge of a planet's ring
- ripper tines: see CAESAR
- RISE: see Liverpool Telescope
- rise azimuth: see horizontal coordinate system
- rise time: see horizontal coordinate system
- RISE TWINS: see InSight
- RISS (refractive interstellar scintillation): refraction of star light by the ISM
- Ritchey-Chrétien telescope: type of two-mirror reflector telescope
- RIX: enquiry/answer about some issue regarding a project review
- RKA (Roscosmos): Russian organization for space technology and research
- RL: see rare designator prefixes
- RLO: see Roche lobe
- RLOF: see Roche lobe
- Roche limit: nearest a body can orbit another and survive
- RLQ: see quasar
- RLS: see Rosalind Franklin
- RLWT: see rare designator prefixes
- RM (Rossiter-McLaughlin effect): effect of transit on visible spectrum of the star
- RM: see Faraday rotation
- Rm: see Reynolds number
- RM effect (Rossiter-McLaughlin effect): effect of transit on visible spectrum of the star
- RMB: see rare designator prefixes
- RMC (Radcliffe Observatory Magellanic Clouds Catalogue): catalog of stars in
- RMC: see Ariel 5
- RMC: see Small Astronomy Satellite 3
- RMHD: see hydrodynamics
- RMK: see double star designation
- RMS: square root of the average of the squares of some values
- rms (RMS): square root of the average of the squares of some values
- RMS amplitude: see amplitude
- RMS astronomy: collective term for radio, millimeter, and submillimeter
- rms wavefront error: see wavefront error
- RNGC: see New General Catalogue
- RNGC/IC: see New General Catalogue
- RNO: see rare designator prefixes
- Ro (Rossby number): ratio of inertial to Coriolis force
- Ro: see rare designator prefixes
- ROA: see rare designator prefixes
- ROACH2: see CASPER
- roAp star: see Ap star
- ROB: see rare designator prefixes
- Rob: see rare designator prefixes
- Robert C. Byrd Green Bank Telescope (Green Bank Telescope): West Virginia large radio telescope
- Robertson-Walker metric: see metric
- Robertson-Walker scale factor (scale factor): relative size of the universe as a function of time
- RoboHARPS
- RoboNet: global network of robotic telescopes to follow up on GRBs
- RoboNet-1.0: see RoboNet
- RoboNet-II: see RoboNet
- robotic fiber positioner (fiber positioner): machine to set up fibers in multi-object spectrograph
- Robotic Optical Transient Search Experiment (ROTSE): automated array of telescopes to uncover and track transients
- Robotically Controlled Telescope: see Kitt Peak National Observatory
- robust association of massive baryonic object (RAMBO): proposed astronomical objects comprising dark matter
- Roche limit: nearest a body can orbit another and survive
- Roche lobe: region of a body's gravitational influence closest to its competitor
- Roche lobe: region of a body's gravitational influence closest to its competitor
- Roche limit: nearest a body can orbit another and survive
- Roche lobe overflow: see Roche lobe
- Roche limit: nearest a body can orbit another and survive
- Roche radius (Roche limit): nearest a body can orbit another and survive
- Roche lobe: region of a body's gravitational influence closest to its competitor
- Roche sphere: see Hill radius
- Roche lobe: region of a body's gravitational influence closest to its competitor
- rock
- silicate: type of compound including silicon and oxygen
- rock vapor phase: see atmosphere formation
- ROCKE-3D: rocky-planet-oriented general circulation model
- rocky planet: planet like Earth and Mars, mostly rock
- Rocky Planet Finder (Automated Planet Finder): robotic telescope to find exoplanets using RV method
- RODEO: code for 2D disk simulation
- ROE: see double star designation
- Roe solver
- RODEO: code for 2D disk simulation
- Roemer delay: timing differences in observed phenomenon due to Earth's position
- Einstein delay: EMR delay due to relativistic effects of environment and motion
- rogue planet (free-floating planet): planet that is not orbiting a star
- rogue planet: see field
- ROLIS: see Rosetta
- rolling Hough transform: see Hough transform
- Roma-BZCAT: 2008 catalog of blazars
- RoMAG: see Tianwen-1
- Roman Space Telescope: proposed near-infrared space observatory
- ROMAP: see Rosetta
- Rome Observatory
- Romulus simulations: cosmological-simulation project active since circa 2015
- ChaNGa: cosmological-simulation project active since circa 2015
- root mean square (RMS): square root of the average of the squares of some values
- RoPeR: see Tianwen-1
- Roque: see rare designator prefixes
- Roque de los Muchachos Observatory: observatory at La Palma in the Canary Islands
- RORF (Radio Optical Reference Frame): 1994 celestial reference frame based on 436 sources
- Rosalind Franklin: Mars rover in development for 2028 launch
- ROSAT: 1990s German space X-ray telescope
- ROSAT All Sky Survey: see ROSAT
- Rosat All-sky Survey
- Rosat Bright Survey: list of bright X-ray sources from ROSAT observations
- ROSAT Deep Cluster Survey: see ROSAT
- ROSAT Deep Survey: see ROSAT
- Rosat Deep Survey
- deep survey: survey using lengthy observation to identify distant galaxies
- Rosat Hard Survey: list of hard X-ray sources from ROSAT observations
- Roscosmos: Russian organization for space technology and research
- Roscosmos State Corporation for Space Activities (Roscosmos): Russian organization for space technology and research
- Rose: see rare designator prefixes
- ROSES (Research Opportunities in Space and Earth Science): NASA program
- Rosetta: space probe that visited a comet
- ROSINA: see Rosetta
- ROSS: see Rapid Eye Mount Telescope
- Ross (Frank Ross's Catalog): high-proper-motion and variable stars catalogued by Frank Ross
- Ross 128 b
- Ross 154: nearby red dwarf
- Ross 248: nearby red dwarf
- Rossby deformation radius (Rossby radius of deformation): length scale where rotation effects are significant
- Rossby number: ratio of inertial to Coriolis force
- Rossby radius of deformation: length scale where rotation effects are significant
- Rossby wave instability: type of disk instability that may be a factor in planet formation
- Rossby waves: meandering shifts in the trajectory of high-altitude winds
- Rosseland mean (Rosseland mean opacity): a useful weighted average of opacities at all the frequencies
- Rosseland mean opacity: a useful weighted average of opacities at all the frequencies
- Rosseland optical depth: see optical depth
- Rossi X-ray Timing Explorer (RXTE): space mission to time X-ray variations
- Rossiter-McLaughlin effect: effect of transit on visible spectrum of the star
- rotating black hole (Kerr black hole): spinning black hole with no charge
- rotating ellipsoidal variable (ellipsoidal variable): binary star elongated by gravity
- rotating ellipsoidal variable: see variable star
- rotating radio transient: radio bursts repeating sporadically
- rotating variable star: see variable star
- rotation
- rotation curve: function mapping distance from galaxy center to orbital speed of stars
- rotation measure: see Faraday rotation
- rotation period: time it takes an astronomical body to revolve
- rotation rate: see rotation period
- rotation speed: see rotation period
- rotational broadening: see line broadening
- rotational ladder: see CO ladder
- rotational modulation: see variable star
- rotational velocity: see stellar rotation
- ROTSE: automated array of telescopes to uncover and track transients
- ROTSE-I: see ROTSE
- ROTSE-II: see ROTSE
- ROTSE-III: see ROTSE
- ROX: see Rho Ophiuchi Cloud Complex
- Royal Astronomy Society: UK society supporting and promoting astronomy
- Royal Astronomy Society of Canada: Canadian society supporting and promoting astronomy
- Royal Greenwich Observatory: former UK national observatory
- Royal University of Edinburgh
- rp-process: synthesis of elements through repeated proton capture
- RPA: see Giotto
- RPC APXS: see Rosetta
- RPF (Automated Planet Finder): robotic telescope to find exoplanets using RV method
- RPI: see IMAGE
- RPS: see ram pressure
- RPW: see Solar Orbiter
- RPWI: see JUICE
- RPWS: see Cassini
- RQQ: see quasar
- RR (RR Lyrae variable): star with periodic variation often in globular clusters
- RR: see rare designator prefixes
- RR Lyrae (RR Lyrae variable): star with periodic variation often in globular clusters
- RR Lyrae star (RR Lyrae variable): star with periodic variation often in globular clusters
- RR Lyrae variable: star with periodic variation often in globular clusters
- RR Lyrae variable: see variable star
- RRab: see RR Lyrae variable
- RRAT (rotating radio transient): radio bursts repeating sporadically
- RRc: see RR Lyrae variable
- RRd: see RR Lyrae variable
- RRL (RR Lyrae variable): star with periodic variation often in globular clusters
- RS (radio source): astronomical object producing observable radio
- RS: see MESSENGER
- RS: see Mars Observer
- RS: see SELENE
- RS: see rare designator prefixes
- RS: see turn-off point
- radio science: radar and other methods of using radio to probe planets and moons
- RS Canum Venaticorum star: see variable star
- RS Canum Venaticorum variable: see variable star
- RS model (Randall-Sundrum model): particular 5-dimensional cosmological model
- RS Oph (RS Ophiuchi): Milky Way recurrent nova
- RS Ophiuchi: Milky Way recurrent nova
- RSA (Roscosmos): Russian organization for space technology and research
- RSA: see Shapley-Ames Catalog
- RSAA (Research School of Astronomy and Astrophysics): Australian National University astrophysics school
- RSAT: see SELENE
- RSB: see GRAIL
- RSCVn: see variable star
- RSD: see redshift space
- RSDI (reference star differential imaging): identifying speckles by comparing star-images
- RSE: see EnVision
- RSG: see supergiant
- RSGC (red supergiant cluster): stellar cluster with multiple red supergiants
- RSI: see Rosetta
- RSN (radio supernova): supernova that includes a detectable radio emission
- RSR: see Large Millimeter Telescope
- RSS: see Cassini
- RSS: see Southern African Large Telescope
- RSS: see Voyager
- RSS: see turn-off point
- radio science: radar and other methods of using radio to probe planets and moons
- RST (Roman Space Telescope): proposed near-infrared space observatory
- RST: see double star designation
- RSU: see Hubble Space Telescope
- Rsun: see Sun
- rSZ: see Sunyaev-Zel'dovich effect
- rSZE: see Sunyaev-Zel'dovich effect
- RT (radiative transfer): energy transfer in the form of electromagnetic radiation
- RT code (radiative transfer code): computer model of a gas's radiative transfer
- RT instability: result of lighter fluid pushing a heavier fluid
- RTE (equation of radiative transfer): equation describing energy transfer by EMR
- RTG (Radioisotope Thermoelectric Generator): type of spacecraft power source for instruments
- RTM (radiative transfer model): models of radiative transfer, often computerized
- RTSW: see Advanced Composition Explorer
- Ru: see rare designator prefixes
- Rubin Observatory: 8-meter survey reflector telescope under construction in Chile
- Ruiz: see rare designator prefixes
- runaway accretion: see accretion
- runaway greenhouse effect: see greenhouse effect
- runaway growth: see planet formation
- oligarch: term for large planetesimals that dominate
- runaway process: a process with positive feedback so progress speeds progress
- runaway star: see high-velocity star
- Runge-Kutta method: type of numerical method for integration and differential equations
- Russia
- Russian
- Glazar: 1980s UV space telescope on MIR space station
- Kvant 1: scientific module on Mir space station
- Orion space telescopes: two Russian 1970s UV space telescopes
- Spektr-R: 10 m space radio telescope
- Spektr-RG: Russian-German X-ray observatory launched in 2019
- Rutherford-Bohr model (Bohr model): has electrons circling nucleus in quantized orbits
- RV (radial velocity): component of velocity toward or away from observer
- RV method (radial velocity method): method of detecting exoplanets and binary companions
- RV method: see extra-solar planet
- RV method: see radial velocity
- 51 Pegasi b: first exoplanet found orbiting a main sequence star
- 55 Cancri e: super-Earth orbiting a Sun-like star
- Automated Planet Finder: robotic telescope to find exoplanets using RV method
- CRIRES: high resolution IR echelle spectrometer
- EXOFAST: code to match model parameters with exoplanet observation data
- Gliese 436 b: hot Neptune found in 2004
- HARPS: high-precision spectrograph for exoplanet searches
- HARPS-N: high-precision spectrograph for exoplanet searches in Canary Islands
- HD 209458 b: hot Jupiter discovered in 1999
- HD 80606 b: hot Jupiter discovered in 2001
- HRS: high resolution spectrography
- Keck Planet Finder: Keck I spectrograph for RV measurements
- minimum mass: measured bound on the mass of an exoplanet
- NGC 3201: globular cluster in which a black hole has been identified
- NIRPS: near-infrared extension to HARPS spectrograph
- PLATO: planned observatory-satellite aimed at finding exoplanets
- Proxima b: exoplanet orbiting Proxima Centauri
- telluric line: absorption line in ground observation due to Earth atmosphere
- RV observatory: see radial velocity
- RV Tauri variable
- RVS: see Gaia
- RWI (Rossby wave instability): type of disk instability that may be a factor in planet formation
- RX: see ROSAT
- RX J0822-4300: see Puppis A
- RXC: see ROSAT
- RXJ1615: protostar with transition disk showing rings
- RXJ1615.3-3255 (RXJ1615): protostar with transition disk showing rings
- RXTE: space mission to time X-ray variations
- Rydberg (Rydberg unit): unit of energy near 13.6 eV
- Rydberg constant: constant used in calculating atomic Hydrogen lines
- 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
- Humphreys series: hydrogen lines for electrons settling from n > 6 to n = 6
- hydrogen: most prominent element, atomic number 1
- Lyman series: hydrogen series from electrons settling from n > 1 to n = 1
- 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
- Rydberg unit: unit of energy near 13.6 eV
- Rydberg constant for deuterium
- Rydberg formula: see Rydberg constant
- hydrogen: most prominent element, atomic number 1
- Rydberg unit: unit of energy near 13.6 eV
- energy: physical state needed to do something
- Ryugu
- Hayabusa2: JAXA mission that returned a sample of an asteroid
Index