Term Index (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
  • neutron capture: combination of an atomic nucleus and a neutron
  • s-process: synthesis of elements through neutron capture and beta decay
  • trans-iron element: elements with atomic number greater than that of iron
• r₀: see seeing
• R₂₀₀: see cluster radius
• R_200c: see cluster radius
• R_200m: see cluster radius
• R₅₀₀: see cluster radius
• R_500c: see cluster radius
• R_⁴He: see Lyman series
• R_D: see Lyman series
  • Rydberg constant: constant used in calculating atomic Hydrogen lines
• R_e (effective radius): radius of a galaxy within which 1/2 the light is emitted
• r_g: see Schwarzschild radius
• R_H (Holmberg radius): a measure of size of galaxy based on surface brightness
• R_H (Rydberg constant): constant used in calculating atomic Hydrogen lines
• R_HO (Holmberg radius): a measure of size of galaxy based on surface brightness
• r_L (Laplace radius): a radius for a stable orbit of a satellite around a planet
• R_m: see Reynolds number
• R_S (Schwarzschild radius): radius of a black hole's event horizon
• R_sp: 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
  • chirp: burst of signal rising or falling in frequency
  • frequency modulation: changing the frequency of a signal's carrier
  • Magellan: 1980s/1990s Venus probe
  • radio science: radar and other methods of using radio to probe planets and moons
  • synthetic aperture radar: method of using moving radar with a stationary target
• Radcliffe Magellanic Clouds (Radcliffe Observatory Magellanic Clouds Catalogue): catalog of stars in
• Radcliffe Observatory
• Radcliffe Observatory Magellanic Clouds Catalogue: catalog of stars in
• 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
  • streaming instability: type of interplay between disk gas and solids that brings solids together
• 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
  • CfA digital speedometer: 1980s/90s spectrograph aimed at radial velocity measurements
  • Doppler shift: wave frequency difference due to relative velocity difference with source
  • General Catalogue of Stellar Radial Velocities: 1950s century catalog of 15000 stars with their radial velocities
  • radial velocity method: method of detecting exoplanets and binary companions
  • stellar kinematics: science of the movement of stars
• 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
  • irradiance: EMR power reaching a surface
  • Planck function: yields black-body spectrum curve
  • radiative transfer: energy transfer in the form of electromagnetic radiation
• 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
• particle spectrometer: device to determine the characteristics of incoming particles
• 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
  • stellar structure: the presumed internal structure of stars
• radiation-dominated era (radiation era): early-universe era when radiation pressure dominated
• radiative cooling timescale: see timescale
• radiative diffusion: see radiation zone
• radiative equilibrium
• thermal equilibrium: state of a system with no net heat flows
• 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
• e-folding time: time to increase by a factor of e
• 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
  • absorption: removal of photons from a beam of EMR
  • CMFGEN: RT code designed to handle significant stellar wind
  • DISORT: simulation of radiative transfer in an atmosphere
  • Eddington approximation: approximation of a star's internal EMR's divergence from isotropic
  • emission: addition of photons to a beam of EMR
  • gray atmosphere: a model atmosphere whose opacity does not depend upon wavelength
  • Hyperion: Monte Carlo radiative transfer code
  • Mie scattering: scattering of light by large particles
  • PICASO: rt code specifically for exoplanet transmission spectroscopy
  • RADEX: radiative transfer code
  • radiation hydrodynamics: hydrodynamics plus the effects of EMR
  • radiation zone: region of a star transmitting energy through radiative diffusion
  • radiative transfer code: computer model of a gas's radiative transfer
  • radiative transfer model: models of radiative transfer, often computerized
  • scattering: changing the direction of a particle's movement
  • self-absorption: EMR absorption by the same substance that emitted it
  • Sobolev approximation: tractable model used in specific kinds of spectral line analysis
  • source function: measure indicating the effect of a material on EMR passing through
  • stellar structure: the presumed internal structure of stars
  • stimulated emission: emission triggered by received photons
  • Turtlebeach: radiative transfer code
  • two-stream approximation: approximation of a star's internal EMR's divergence from isotropic
• 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: energy transfer in the form of electromagnetic radiation
  • source function: measure indicating the effect of a material on EMR passing through
• 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
  • ARISE: concept for an inflated 25-meter radio telescope in space
  • 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: advanced 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
  • FARSIDE: concept for a low-frequency radio telescope on the far side of the Moon
  • FarView: concept for a low-frequency radio telescope on the far side of the Moon
  • 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
  • Güdel-Benz relation: relation between X-rays and radio from stars
  • 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
  • LCRT: concept for a dish radio telescope in a lunar crater
  • 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
• downconverter: device that reduces the frequency of a signal
• intensity interferometer: interferometer based upon interference from intensity variations
• 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
  • core collapse supernova: supernova resulting from the collapse of the core of a star
• radio telescope: telescope that operates in the radio frequency range of EMR
• radio transient: see transient
• radio transients
• Canadian Hydrogen Intensity Mapping Experiment: radio telescope mapping distant neutral hydrogen
• Tianlai Project: 21-cm line intensity mapping project
• radio waves (radio): electromagnetic radiation, frequency 3 kHz to 300 GHz
• radio window: see atmospheric window
  • radio astronomy: astronomy observation and analysis of radio EMR
• 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 heating: a source of heat of some planets and moons
• 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
  • beta decay: radioactivity such that an electron or positron is emitted
  • quantum tunneling: quantum mechanical effect of particles passing through a barrier
  • radioactive dating: determining the age of a substance that has a radioactive component
  • radioactive heating: a source of heat of some planets and moons
  • valley of beta stability: set of isotopes not prone to beta decay
• RadioAstron
• Spektr-R: 10 m space radio telescope
• 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
• cluster radius: radius of a galaxy cluster
• Hill radius: radius of gravitational influence of a body
• Kepler radius: radius at which a particular velocity would orbit
• Laplace radius: a radius for a stable orbit of a satellite around a planet
• magnetospheric truncation radius: radius at which the disc ram pressure matches the magnetic field pressure
• mass-radius relation: model relating stellar mass and radius
• Roche lobe: region of a body's gravitational influence closest to its competitor
• stellar radius determination: methods by which the radius of a star is determined
• 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
  • Fenton Hill Observatory: New Mexico GRB-oriented astronomical observatory
• 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
  • Massive Cluster Survey: survey of distant clusters evident in ROSAT X-ray data
  • RASS/Green Bank Catalog: combined list of radio galaxies from Rosat and Green Bank surveys
• 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
• alpha CO: ratio of CO emissions to H₂
• CO to H₂ factor: assumed ratio between observed CO emission lines and H₂ mass
• combined differential photometric precision: calculated relation of photometric variation to SNR
• gas-to-dust ratio: mass ratio of gas to dust, such as within a SF region
• Jeans parameter: ratio measuring a tendency of an atmosphere to escape
• mass-to-light ratio: measure of a population of stars or region
• signal-to-noise ratio: ratio of the power of a signal to the power of the background noise
• Stokes number: measure of a particle's tendency to follow the flow of a fluid
• Strehl ratio: measure of optical aberration
• 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
• Wien approximation: yields approximation of black body curve useful at short wavelengths
• 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
  • spectral index: power by which an object's flux depends on frequency
• 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
  • Astronet: European astronomy consortium
• 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
• Fenton Hill Observatory: New Mexico GRB-oriented astronomical observatory
• reaction
• carbon burning: fusion reaction starting with carbon
• CNO cycle: fusion reaction chain turning hydrogen and nitrogen into helium and nitrogen
• deuterium burning: any fusion reaction starting with deuterium
• electron capture: combination of an electron with a proton
• helium burning: fusion reaction starting with helium
• hydrogen burning: any fusion reaction starting with hydrogen
• lithium burning: any fusion reaction starting with lithium
• neon burning: fusion reaction starting with neon
• oxygen burning: fusion reaction starting with oxygen
• proton-proton chain: type of fusion reaction chain turning hydrogen into helium
• silicon burning: alpha process fusion starting at silicon
• triple alpha process: fusion reaction chain turning helium-4 into carbon
• 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
  • baryon acoustic oscillations: density fluctuations stemming from acoustic waves in the early universe
  • cosmic microwave background: microwave radiation coming from every direction
  • dark age: interval when the universe's hydrogen atoms were neutral
  • early universe: from the Big Bang to recombination
  • observable universe: that part of the universe that we can conceivably observe
  • Sachs-Wolfe effect: gravitational redshift of the CMB
• 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
  • T Coronae Borealis: recurrent nova expected to erupt sometime within 2024-2026
  • T Pyxidis: well-known recurrent 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
  • elliptical galaxy: ellipsoidal-shaped galaxy
  • galaxy main sequence: relation between galaxies' star formation and stellar mass
• 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
  • AD Leonis: active red dwarf
  • Barnard's Star: nearby red dwarf
  • G239-25: nearby red dwarf with brown dwarf companion
  • Lacaille 9352: red dwarf that is the twelfth nearest star system
  • Lalande 21185: nearby red dwarf
  • LHS 1140: red dwarf with rocky planet in its habitable zone
  • Ross 154: nearby red dwarf
  • Ross 248: nearby red dwarf
  • Scholz's Star: nearby binary star with red dwarf and brown dwarf
  • Teegarden's Star: nearby red dwarf
  • TRAPPIST-1: red dwarf with exoplanets within the habitable zone
  • Wolf 359: nearby red dwarf
• 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
• Taylor-Proudman theorem: theorem regarding movement through a rotating fluid
• 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
  • tip of the red-giant branch: standard candle consisting of the brightest RGB stars
• 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
  • reduction potential: measure of a chemical species' tendency to acquire electrons
• redox potential (reduction potential): measure of a chemical species' tendency to acquire electrons
• redshift: change to longer wavelengths due to Doppler effects
  • 21-cm experiment: search for redshifted 21-cm hydrogen emission lines
  • 21-cm line: hydrogen line useful for determining redshift
  • 2dF Galaxy Redshift Survey: imaging survey of 300,000 extragalactic objects
  • 2MASS Photometric Redshift Catalog: galaxy redshifts from 2MASS
  • Alcock-Paczyński effect: type of distortion of the apparent depth of galaxy clusters
  • blue shift: shortening of wavelengths due to Doppler effects
  • Butcher-Oemler effect: observation of more blue galaxies at z > 0.3
  • Canada-France Redshift Survey: 1990s survey of galaxies to z = 1 to find associations of redshift to characteristics
  • CfA Redshift Survey: 1970s-1990s surveys of galaxy redshifts
  • cosmological redshift: redshift of distant objects due to the Hubble expansion
  • DEEP2: redshift survey of 60,000 galaxies
  • Doppler shift: wave frequency difference due to relative velocity difference with source
  • Euclid: survey observatory-satellite to measure dark energy
  • Faint Infrared Grism Survey: survey to identify redshift of distant galaxies
  • Hubble diagram: diagram comparing redshift with distance
  • ionized carbon fine structure line: carbon line that traces distant star formation
  • K correction: correction to magnitude for redshift
  • Las Campanas Redshift Survey: 1990s survey of galaxies out to z = 0.2
  • line broadening: processes causing a spectral line to have width
  • Low-frequency Array: low frequency radio telescope
  • Lyman-alpha emitter: redshifted galaxy emitting the Lyman alpha line
  • Lyman-alpha forest: overlaid redshifted Lyman-alpha absorption lines on light from distant objects
  • Molecular Deep Field: survey of molecular lines in Hubble Deep Field
  • Murchison Widefield Array: low frequency radio telescope
  • photometric redshift: method of estimating redshift without spectroscopy
  • redshift space: concept of space using redshift as the radial dimension
  • redshift survey: survey of the universe aiming at three dimensions
  • rest wavelength: normal wavelength observed when not moving in relation to the source
  • Rossiter-McLaughlin effect: effect of transit on visible spectrum of the star
  • Southern Sky Redshift Survey: 1980s/1990s redshift survey of southern galaxies
  • tired light: an alternate theory explaining the cosmological redshift
  • VIMOS Public Extragalactic Redshift Survey: spectrographic redshift survey of 80,000 galaxies
  • WiggleZ: survey aimed at mapping dark energy
  • WISE x SuperCOSMOS photometric redshift catalog: catalog of distant galaxies in WISE and SuperCOSMOS
• Redshift Evolution and Formation in Extragalactic Systems (REFINE): catalog of high-redshift galaxies
• redshift parameter (redshift): change to longer wavelengths due to Doppler effects
  • blue shift: shortening of wavelengths due to Doppler effects
  • cosmological redshift: redshift of distant objects due to the Hubble expansion
• redshift space: concept of space using redshift as the radial dimension
  • Alcock-Paczyński effect: type of distortion of the apparent depth of galaxy clusters
  • data cube: three-dimensional array of numerical data
• redshift space distortion: see redshift space
  • Alcock-Paczyński effect: type of distortion of the apparent depth of galaxy clusters
• 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
  • Compton wavelength: lower bound on a particle's possible de Broglie wavelength
• reducing agent: see reducing atmosphere
• reducing atmosphere: atmosphere lacking oxygen and other oxidizers
• reduction: see reducing atmosphere
  • oxidation state: number of electrons loaned out by an atom in an ionic bond
  • reduction potential: measure of a chemical species' tendency to acquire electrons
• 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
• retrograde orbit: orbit opposite the usual direction
• reference star
• reference star differential imaging: identifying speckles by comparing star-images
• 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
  • emission nebula: nebula that emits light such as an HII region or PN
• reflection spectroscopy
• transmission spectroscopy: spectrum of radiation passing through a substance
• reflective grating: see grating
• reflector (reflector telescope): telescope using mirrors rather than lenses to magnify
  • adaptive optics: optical mechanism to compensate for varying atmospheric distortion
  • Anglo-Australian Telescope: 3.9-m reflector telescope in Australia
  • ANU 2.3m Telescope: 2.3-m telescope at Siding Spring Observatory
  • Archeops: balloon-borne 1.3 m submillimeter telescope
  • ARISE: concept for an inflated 25-meter radio telescope in space
  • ARO 12m Telescope: twelve meter microwave telescope at KPNO
  • ASTHROS: balloon-borne 2.5-m submillimeter telescope
  • Atacama Submillimeter Telescope Experiment: 10-meter submillimeter telescope in Chile
  • AtLAST: concept for submillimeter survey telescope in Chile
  • BLAST: balloon-borne 1.8-m submillimeter telescope
  • BOOMERanG: 1990s-2000s balloon-borne 1.3-meter millimeter telescope
  • Caltech Submillimeter Observatory: 10.4 meter submillimeter telescope previously in Hawaii
  • Canada-France-Hawaii Telescope: 3.6-meter optical/infrared telescope in Hawaii
  • Cassegrain reflector: reflector telescope with convex secondary mirror
  • CHEOPS: space telescope in development to measure radii of exoplanets
  • coudé focus telescope: type of Nasmyth telescope with additional mirrors
  • Dall-Kirkham telescope: type of reflector telescope
  • Darwin: past plan for space telescopes acting as an interferometer
  • Dragone telescope: off-axis reflector telescope type that preserves polarization
  • Dragonfly Telephoto Array: Canadian compact array of small visible-light telescopes
  • ESO 3.6m Telescope: reflector telescope at La Silla
  • ESO Schmidt Telescope: 1 meter telescope in Chile with a wide field-of-view
  • ESPEX: concept for a small near-UV/optical space observatory
  • Euclid: survey observatory-satellite to measure dark energy
  • European Extremely Large Telescope: 39-meter telescope under construction
  • extreme adaptive optics: high-performance version of AO system
  • Extreme Ultraviolet Explorer: 1990s ultraviolet space telescope
  • extremely large telescope: optical telescope with a 20+ meter aperture
  • fold mirror: flat mirror in a telescope to redirect the light
  • Gaia: astrometry survey satellite launched in 2013
  • Giant Magellan Telescope: 24.5 meter telescope under construction
  • Gran Telescopio Canarias: 10.4 meter telescope in the Canary Islands
  • Gregorian telescope: type of reflector telescope
  • GUSTO: balloon-borne 0.9-m far-infrared telescope
  • HabEx: proposed space mission to directly image exoplanets
  • Hale Telescope: 5.1 m reflector telescope in California
  • Herschelian telescope: type of off-axis reflector telescope
  • High Definition Space Telescope: proposed 12-meter space telescope
  • Hiltner Telescope: 2.4-meter reflector telescope at MDM observatory
  • Hobby-Eberly Telescope: 10 meter telescope in Texas
  • Hubble Space Telescope: observatory-satellite with 2.4-meter reflective telescope
  • Infrared Space Observatory: 1990s 60-cm infrared space telescope
  • Infrared Survey Facility: 140 cm reflector telescope that images in infrared
  • International Liquid Mirror Telescope: 4-meter liquid mirror telescope under construction in India
  • IRTF: Mauna Kea 3-meter infrared telescope
  • Isaac Newton Telescope: 2.5 m telescope in Canary Islands
  • James Clerk Maxwell Telescope: far-infrared telescope in Hawaii
  • James Webb Space Telescope: 6.5-meter infrared space telescope at L2
  • K2: second Kepler mission that worked around failed equipment
  • Keck Observatory: observatory in Hawaii with two 10-meter reflectors
  • Kepler Telescope: space telescope that watched stars for exoplanets
  • Korsch telescope: type of three-mirror reflector telescope
  • LAMOST: Chinese telescope for spectroscopic surveys of stars and galaxies
  • Large Altazimuth Telescope: 6-meter reflector telescope in Russia
  • Large Binocular Telescope: dual 8.4 meter telescope in Arizona
  • Large Millimeter Telescope: large microwave telescope in Mexico
  • Large Submillimeter Telescope: concept for a 50-meter submillimeter telescope in Chile
  • Large Zenith Telescope: 6 meter liquid mirror telescope in British Columbia
  • LCRT: concept for a dish radio telescope in a lunar crater
  • liquid mirror telescope: reflector telescope with primary mirror formed of spinning liquid
  • Liverpool Telescope: 2-meter robotic telescope in Spain
  • Lowell Discovery Telescope: 4.3 m telescope at Lowell Observatory, Arizona
  • Magellan Telescopes: pair of 6.5 m optical telescopes in Chile
  • MAXIMA: 1998-1999 balloon-borne 1.3-meter millimeter telescope
  • Mayall 4m Telescope: 4 meter reflector telescope at Kitt Peak
  • MeerLICHT: South African telescope coordinated with MeerKAT
  • Mercator Telescope: 1.2 m telescope in the Canary Islands
  • mirror support cell: units in a telescope that support the mirror
  • MMT: 6.5 meter telescope at Mt. Hopkins, Arizona
  • Nasmyth telescope: type of reflector telescope with secondary and tertiary mirrors
  • NEO Surveyor: planned space observatory to detect and monitor NEOs
  • New Technology Telescope: 3.58-meter reflector telescope in Chile
  • Newtonian telescope: type of reflector telescope
  • Origins Space Telescope: concept for 2030s large space IR telescope
  • Overwhelmingly Large Telescope: 100 m telescope plan
  • Palomar 48 Inch Telescope: 48 inch Schmidt telescope at Palomar Observatory
  • Palomar 60-inch Telescope: 60 inch telescope at Palomar Observatory
  • PLATO: planned observatory-satellite aimed at finding exoplanets
  • PRIMA: plan for 2030s NASA 1.8-m FIR space telescope
  • primary mirror: main mirror in a reflector telescope
  • prime focus: reflector telescope with no secondary mirror
  • Rapid Eye Mount Telescope: quick-action robotic telescope at La Silla Observatory
  • Ritchey-Chrétien telescope: type of two-mirror reflector telescope
  • Roman Space Telescope: proposed near-infrared space observatory
  • Rubin Observatory: 8-meter survey reflector telescope under construction in Chile
  • Schiefspiegler: type of off-axis reflector telescope
  • Schmidt camera: telescope type with a very wide field of view
  • Schmidt-Newton telescope: type of reflector telescope
  • Schwarzschild telescope: type of two-mirror reflector telescope
  • Shane Telescope: 3.05 m reflector telescope at Lick Observatory
  • SkyMapper: automated 1.35 m optical telescope in Australia
  • Sloan 2.5m Telescope: telescope for SDSS in New Mexico
  • SOAR Telescope: 4.1 m reflector telescope in Chile
  • Southern African Large Telescope: 10-meter telescope in South Africa
  • STUDIO: balloon-borne 0.5 m ultraviolet telescope
  • Subaru Telescope: 8.2-meter telescope in Hawaii
  • Submillimeter Telescope: 10-meter far-infrared telescope
  • SuperBIT: balloon-borne 0.5-m telescope
  • Telescopio Nazionale Galileo: 3.58 m telescope in Canary Islands
  • Terrestrial Planet Finder: plan for space telescopes to find smaller exoplanets
  • Thirty Meter Telescope: extremely large telescope planned for Hawaii
  • three-mirror anastigmat: general type of reflector telescope
  • Transiting Exoplanet Survey Satellite: observatory-satellite searching for transiting exoplanets
  • TRAPPIST: a ground-based automated transiting-planet finding telescope
  • UK Schmidt Telescope: 1.2 meter telescope in Australia with wide field-of-view
  • United Kingdom Infrared Telescope: Mauna Kea 3.8 meter infrared telescope
  • University of Tokyo Atacama Observatory: observatory for a 6.5 m infrared telescope under construction
  • Víctor M. Blanco Telescope: 4 meter reflector telescope in Chile
  • VISTA: 4.1 meter telescope in Paranal Observatory in Chile
  • Wide Field Infrared Explorer: partly-failed 1999 infrared satellite
  • Wide-field Infrared Survey Explorer: infrared space telescope aimed at an all-sky survey
  • William Herschel Telescope: 4.2-meter telescope in the Canary Islands
  • WIYN 3.5m Telescope: Kitt Peak telescope run by university collaboration and NOIRLab
  • Yolo telescope: type of reflector telescope
• 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
  • diffraction: an effect of the edge of an obstacle on a wave
  • immersion grating: grating where light is within the material
  • refractive index: measure of how much a material slows down light
  • Snell's law: optical principle of refraction
• refractive index: measure of how much a material slows down light
  • focal length: length from optical element to focal plane
  • immersion grating: grating where light is within the material
  • refraction: redirection of light passing from one medium to another
  • Snell's law: optical principle of refraction
• refractive interstellar scintillation: refraction of star light by the ISM
• refractive scintillation (refractive interstellar scintillation): refraction of star light by the ISM
  • scintillometry: measuring of twinkling
• refractor (refracting telescope): telescope using lenses rather than mirrors to magnify
• refractory (refractory material): material with high condensation temperature
  • volatile material: material with low condensation temperature
• refractory compound: see refractory material
  • volatile material: material with low condensation temperature
• refractory element: see refractory material
  • volatile material: material with low condensation temperature
• refractory inclusion: see refractory material
• refractory material: material with high condensation temperature
  • volatile material: material with low 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
  • early universe: from the Big Bang to recombination
• 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
  • Kerr black hole: spinning black hole with no charge
• Reissner-Nordström metric: see metric
• Reissner-Nordström object: see black hole model
• relation
• age-metallicity relation: older stars generally have lower metallicity
• age-velocity-dispersion relation: relation between stellar age and peculiar velocity
• de Vaucouleurs' profile: relation between elliptical galaxy surface brightness and distance from center
• dense core mass function: function describing range of masses of dense cores
• Faber-Jackson relation: relation between elliptical galaxy luminosity and stellar velocity dispersion
• Freeman's law: all spiral galaxy's have the same central surface brightness
• fundamental plane: three-way relation between elliptical galaxy characteristics
• Güdel-Benz relation: relation between X-rays and radio from stars
• galaxy main sequence: relation between galaxies' star formation and stellar mass
• gyrochronology: means of estimating stellar age from rotation
• initial mass function: function describing initial mass of stars
• ionization correction factor: relations between ion abundances and element abundances
• Kennicutt-Schmidt law: relation between gas density and star formation rate
• Kormendy Relation: relation between elliptical galaxy luminosity surface brightness
• Kramers opacity law: opacity's relation to density and temperature
• luminosity function: function giving number of stars or galaxies at different luminosities
• M-sigma relation: relation between galaxy center's velocity dispersion and SMBH mass
• main-sequence lifetime: length of time that a star remains within the main sequence
• mass-luminosity relation: model relating stellar mass and luminosity
• mass-radius relation: model relating stellar mass and radius
• morphology-density relation: a galaxy is more likely to be elliptical if surrounded by galaxies
• Sérsic profile: model of the relative surface brightness across a galaxy
• star-formation rate stellar-mass ratio: ratio between a galaxy's stellar mass and its SF rate
• stellar birth rate function: function describing the birth rate of stars by mass
• surface brightness fluctuation: apparent indication of an elliptical galaxy's distance
• Tully-Fisher relation: relation between spiral galaxy luminosity and line width
• velocity-metallicity relation: higher stellar velocity correlates with lower metallicity
• Wilson-Bappu effect: a relation between a star's spectral line and luminosity
• X-ray luminosity function: maps X-ray luminosities to count of such sources
• zero-age main sequence: describes stars that just began hydrogen fusion
• 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
  • radiation hydrodynamics: hydrodynamics plus the effects of EMR
• 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
  • Chern-Simons gravity: one type of modified general relativity
  • chirp mass: a reduced-mass-like quantity that relates to gravitational waves
  • continuous gravitational wave: long-lasting repeating GWs such as from orbits
  • cosmic string: rent in spacetime
  • cosmological constant: force counteracting the universe's inward gravitational pull
  • Einstein delay: EMR delay due to relativistic effects of environment and motion
  • ergosphere: type of region of space around rotating black hole
  • frame dragging: region of space dragged into rotation by a rotating object
  • frame of reference: region, possibly in motion, from which something is observed/considered
  • general relativity: formula relating gravity, space, time, and mass
  • gravitational wave: ripples in the curvature of spacetime propagating as a wave
  • gravitational wave background: combination of weak gravitational waves such as from distant sources
  • gravitational wave spectrum: various frequencies of gravitational waves
  • gravitational wave strain: a measure of the magnitude of a gravitational wave
  • gravitational-wave memory: a gravitational wave that does not return
  • gravitomagnetic field: magnetic-like-field produced by gravitation
  • gravity: theory that mass attracts
  • Gravity Probe B: space experiment re GR effects of Earth gravity
  • HARM: code to solve GRMHD problems
  • Hartle-Thorne metric: metric approximating GR effects of slow neutron star rotation
  • Johannsen-Psaltis metric: metric template allowing metrics to be written as a general expansion
  • Kerr-NUT spacetime: Kerr spacetime defined in terms of Taub-NUT spacetime
  • law of cosmic censorship: a singularity cannot be observed
  • Lense-Thirring effect: effect on precession from frame dragging
  • light cone: region of space-time which you can see or can see you
  • Lorentz transformation: equations describing the effect of relative motion on length and velocity
  • Lovelock gravity: generalization of general relativity
  • mass: object's quality that determines the effects of forces and gravity
  • metric: mathematical generalization of the concept of distance
  • nanohertz gravitational waves: size of GWs that pulsar-timing observations might catch
  • Newton's laws: physical laws of dynamics and gravitation
  • numerical relativity: solving GR-sensitive problems with numerical methods
  • observable universe: that part of the universe that we can conceivably observe
  • parameterized post-Newtonian formalism: method of approximating GR-based gravity from Newtonian gravity
  • particle horizon: furthest point from which light can reach us
  • photon sphere: surface surrounding black hole where photons can orbit
  • post-Newtonian formalism: method of approximating GR-based mechanics from Newtonian mechanics
  • primordial gravitational waves: gravitational waves formed in the early universe
  • relativistic astrophysics: physics applicable to cosmology and strong field gravity
  • relativistic beaming: directional relativistic effect on light from relativistic speeds
  • relativistic effect: a substantial fraction of the speed of light
  • relativistic energy: energy of an object including relativistic effects
  • relativistic invariance: quantity that remains the same regardless of frame of reference
  • relativistic momentum: momentum of an object including relativistic effects
  • Shapiro delay: EMR delay due to passing near massive object
  • spacetime: four dimensions: time and the three space dimensions
  • spacetime diagram: graph of simplified spacetime, with fewer space dimensions
  • SpEC: code to solve general relativity problems
  • Taub spacetime: early 1950s model for a rotating-black-hole spacetime
  • Taub-NUT spacetime: early mathematics for a rotating black hole spacetime
  • theoretical modified GR metric: metric devised to define modifications to GR
  • time dilation: relativity's ability to make time differ for different objects
  • time standard: method of designating points in time and quantifying time periods
  • Tolman VII object: theoretical object adhering to exact GR solution
  • topological defect: defect in space that could arise in the early universe
  • white hole: the inverse of a black hole, into which matter cannot enter
  • worldline: path of an object through space and time
• relaxation: see relaxation time
  • lattice Boltzmann method: computational fluid dynamics method treating the fluid as particles
• relaxation time: time associated with exponential falloff
  • e-folding time: time to increase by a factor of e
  • 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
  • cosmic background radiation: electromagnetic radiation coming from every direction
• 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
• position-position-velocity space: 3D space concept using velocity as one of the three dimensions
• 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
• Lindblad resonance: resonant orbits within a disk due to a high-density portion
• Lindblad torque: torque due to Lindblad resonances
• orbital resonance: tendency of orbits of multiple bodies to remain in a simple pattern
• Q factor: measure of oscillator's damping
• 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
  • relativistic energy: energy of an object including relativistic effects
  • relativistic momentum: momentum of an object including relativistic effects
• 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
• Milky Way subgroup: the Milky Way and its satellites
• 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
  • planetary migration: change in planet's orbit
  • retrograde hot Jupiter: large hot planet orbiting opposite the expected direction
  • Triton: Neptune's one significant moon
• 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
  • AGN corona: plasma surrounding or near an AGN
• 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
• Reynolds decomposition: mathematical separation of average and fluctuating parts of a quantity
• RF (radiative forcing): difference between a planet's incoming and outgoing radiation
  • downconverter: device that reduces the frequency of a signal
• RF interference (radio frequency interference): transmissions in a frequency band under observation
  • radiative forcing: difference between a planet's incoming and outgoing radiation
• 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
  • blue loop: stellar evolutionary-track segment due to short-term helium burning
  • red giant: very bright red star
  • tip of the red-giant branch: standard candle consisting of the brightest RGB stars
• 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
• hypergiant: extremely bright stars
• Rho Ophiuchi
• Rho Ophiuchi Cloud Complex: nebula that is a nearby star-forming region
• 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
• High Elevation Antarctic Terahertz Telescope: 61 cm FIR telescope in Antarctica
• 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
• polarization: property of waves that oscillate in a particular direction
• specific angular momentum: absolute angular momentum divided by mass
• 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
  • Hoag's Object: peculiar ring galaxy
• 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
  • neutron star merger: two neutron stars meeting and forming one
• 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
  • scintillometry: measuring of twinkling
• 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
  • quadratic field strength: a measure of a star's varying magnetic field
  • RMS astronomy: collective term for radio, millimeter, and submillimeter
• 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
• Terra Hunting Experiment: search for exoplanets using HARPS3
• 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
  • SuperCOSMOS Sky Survey: survey of stars and galaxies from legacy plates
• 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
  • WISE 0855-0714: nearby brown dwarf
• 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
• Campo Imperatore Near-Earth Object Survey: survey of near-Earth objects
• 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
  • quadratic field strength: a measure of a star's varying magnetic field
  • RMS astronomy: collective term for radio, millimeter, and submillimeter
• RoPeR: see Tianwen-1
• Roque: see rare designator prefixes
• Roque de los Muchachos Observatory: observatory at La Palma in the Canary Islands
  • Carlsberg Meridian Catalogue: series of astrometric catalogs from 19th century on
  • GOTO: telescope array to follow up gravitational wave signals
  • Gran Telescopio Canarias: 10.4 meter telescope in the Canary Islands
  • Instituto de Astrofísica de Canarias: research institute on Canary Islands
  • Isaac Newton Group of Telescopes: three telescopes in Canary Islands
  • Isaac Newton Telescope: 2.5 m telescope in Canary Islands
  • MASCARA: distributed array of telescopes to search for exoplanets
  • Mercator Telescope: 1.2 m telescope in the Canary Islands
  • STELLA: two robotic telescopes in Canary Islands
  • Telescopio Nazionale Galileo: 3.58 m telescope in 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
  • RASS/Green Bank Catalog: combined list of radio galaxies from Rosat and Green Bank surveys
  • Rosat Bright Survey: list of bright X-ray sources from ROSAT observations
  • Rosat Hard Survey: list of hard X-ray sources from ROSAT observations
• ROSAT All Sky Survey: see ROSAT
  • Massive Cluster Survey: survey of distant clusters evident in ROSAT X-ray data
• Rosat All-sky Survey
• RASS/Green Bank Catalog: combined list of radio galaxies from Rosat and Green Bank surveys
• 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
  • ExoMars: program to search for signs of life on Mars
  • Rosalind Franklin: Mars rover in development for 2028 launch
  • Trace Gas Orbiter: ESA and Russian Mars orbiter-probe launched in 2016
• 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
• exo-Earth: Earth-like exoplanet
• 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
  • inertial wave: type of wave in a rotating fluid
• 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
  • transient: observed change in the sky
• rotating variable star: see variable star
• rotation
• anomalous X-ray pulsar: X-ray pulsars with no high-mass companion
• atmospheric tide: tide-type movement within the atmosphere
• Be star: early star with Balmer emission lines
• Chandler wobble: shifting of the Earth's axis of rotation relative to the Earth itself
• core-cusp problem: theories and observation show different dwarf galaxy rotation curves
• Coriolis force: apparent force in a rotating frame of reference
• ergosphere: type of region of space around rotating black hole
• Faraday rotation: rotation of optical polarization by a medium in a magnetic field
• frame dragging: region of space dragged into rotation by a rotating object
• gyrochronology: means of estimating stellar age from rotation
• Mach's principle: the notion that rotation is relative to all the mass of the universe
• magnetic dipole braking: the effect of a reduction in the spinning of a magnetic field
• magnetic dipole radiation: EMR naturally generated by a spinning magnetic dipole
• millisecond pulsar: pulsar spinning with a period in the range of milliseconds
• nutation: precession of a body's axis of rotation
• Oort constants: two constants characterizing local Milky-Way motion
• P-Pdot diagram: diagram comparing the rotation and the slowing of pulsars
• period derivative: rate of change in the period of an orbit or rotation
• precession: periodic change in a body's rotation or orbit
• precession of the equinoxes: Earth axial precession with a 26000-year cycle
• pulsar: type of astronomical body with EMR in regular cycles of seconds or less
• pulsar characteristic age: approximate age determination of a pulsar based upon rotation rate
• retrograde accretion: accretion disk spinning in opposite direction to the body
• retrograde hot Jupiter: large hot planet orbiting opposite the expected direction
• retrograde orbit: orbit opposite the usual direction
• Rossby number: ratio of inertial to Coriolis force
• rotation curve: function mapping distance from galaxy center to orbital speed of stars
• rotation period: time it takes an astronomical body to revolve
• shell star: type of star with broad and narrow absorption lines
• specific angular momentum: absolute angular momentum divided by mass
• spin-down luminosity: pulsar's energy extracted from slowing rotation
• spinning dust emission: source of microwave signal
• stellar rotation: rotation of a star around an axis through the middle
• synchronous orbit: orbit with angular velocity matching the rotation of the orbited body
• Taylor-Proudman theorem: theorem regarding movement through a rotating fluid
• theory of figures: type of model relating a planet's shape to its rotation
• tidal locking: locked rotation of an orbiting body
• Toomre Q parameter: stability criterion for differentially rotating disks
• Tully-Fisher relation: relation between spiral galaxy luminosity and line width
• vortensity: ratio of vorticity to surface mass-density
• X-ray pulsar: pulsar producing X-rays from accretion
• Yarkovsky effect: force on spinning, orbiting objects from asymmetric radiation
• Yarkovsky-O'Keefe-Radzievskii-Paddack effect: rotational effect on asymmetric asteroids
• rotation curve: function mapping distance from galaxy center to orbital speed of stars
  • Oort constants: two constants characterizing local Milky-Way motion
• rotation measure: see Faraday rotation
• rotation period: time it takes an astronomical body to revolve
  • P-Pdot diagram: diagram comparing the rotation and the slowing of pulsars
  • period derivative: rate of change in the period of an orbit or rotation
• 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
  • Fenton Hill Observatory: New Mexico GRB-oriented astronomical observatory
• 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
• SuperCOSMOS Sky Survey: survey of stars and galaxies from legacy plates
• rp-process: synthesis of elements through repeated proton capture
  • nucleosynthesis: creation of atomic nuclei
• 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
  • kappa mechanism: stellar instability caused by opacity increasing with temperature
  • pulsating star: variable star that varies through energy pulses
  • standard candle: astronomical object whose brightness can be determined
• RRab: see RR Lyrae variable
• RRAT (rotating radio transient): radio bursts repeating sporadically
  • transient: observed change in the sky
• RRc: see RR Lyrae variable
• RRd: see RR Lyrae variable
• RRL (RR Lyrae variable): star with periodic variation often in globular clusters
  • pulsating star: variable star that varies through energy pulses
• 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
  • core collapse supernova: supernova resulting from the collapse of the core of a star
• 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
  • Catalogue of Southern Double Stars: 1955 catalog with multiple star systems and non-orbiting double stars
• 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
  • radiative transfer: energy transfer in the form of electromagnetic radiation
• 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
  • supernova survey: survey to identify and/or study supernovae
• 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
  • hypervelocity star: star moving very much faster than usual
• Runge-Kutta method: type of numerical method for integration and differential equations
• Russia
• Baksan Neutrino Observatory: Russian underground particle detector
• ExoMars: program to search for signs of life on Mars
• GRANAT: observatory-satellite for detecting gamma rays and X-rays
• Large Altazimuth Telescope: 6-meter reflector telescope in Russia
• MASTER Robotic Net: network of automated telescopes to identify transients
• RATAN-600: ring-shaped radio telescope in Russia
• Roscosmos: Russian organization for space technology and research
• Trace Gas Orbiter: ESA and Russian Mars orbiter-probe launched in 2016
• Tunka experiment: Russian Cherenkov detector aimed at cosmic rays and gamma rays
• 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
  • radial velocity method: method of detecting exoplanets and binary companions
• 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
• pulsating star: variable star that varies through energy pulses
• 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 constant: constant used in calculating atomic Hydrogen lines
• 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