Term Index (G)
Astrophysical terms and names of things beginning with the letter G.
G0
G1
G2
G3
GA
GB
GC
GD
GE
GF
GG
GH
GI
GJ
GK
GL
GM
GN
GO
GP
GR
GS
GT
GU
GV
GW
GX
GY
GZ
- G (G band): band of visible light around 5100 angstroms
- G (G-type star): stars spectrally similar to the Sun
- G (Lowell Proper Motion Survey): 1950s-1970s catalogs of stars with proper motion
- G (gauss): measurement of magnetic field β
- G (glycine): smallest of the twenty common amino acids
- G (gravitational constant): indicates how much pull between two masses
- G: see galactic coordinate system
- G: see rare designator prefixes
- g (surface gravity): measure of gravity at the surface of a body
- g: see griz photometric system
- g: see ugriz photometric system
- G 268-38 (LHS 1140): red dwarf with rocky planet in its habitable zone
- G 270-58 (LHS 1140): red dwarf with rocky planet in its habitable zone
- G 29-38 (Giclas 29-38): white dwarf variable star of interest
- G band: band of visible light around 5100 angstroms
- G band: see Gaia
- G dwarf: see G-type star
- G numbers: see Lowell Proper Motion Survey
- g': see ugriz photometric system
- G-APD (Geiger-avalanche photodiode): type of solid state photon sensor
- G-class: see G-type star
- G-class star (G-type star): stars spectrally similar to the Sun
- G-CLEF: spectrograph on the GMT
- G-CLEF: see Giant Magellan Telescope
- G-dwarf problem: lack of metal-poor G dwarfs in the Milky Way
- g-mode: see asteroseismology
- g-r color: difference between SDSS g' and r' magnitudes
- g-r color index (g-r color): difference between SDSS g' and r' magnitudes
- G-type star: stars spectrally similar to the Sun
- G02: see GAMA
- G09: see GAMA
- G1.9+0.3: recent supernova remnant in Sagittarius
- G102: see WFC3
- G12: see GAMA
- G140H: see NIRSpec
- G140M: see NIRSpec
- G141: see WFC3
- G15: see GAMA
- G23: see GAMA
- G235H: see NIRSpec
- G235M: see NIRSpec
- G239-25: nearby red dwarf with brown dwarf companion
- G239-25AB (G239-25): nearby red dwarf with brown dwarf companion
- G280: see WFC3
- G395: see James Webb Space Telescope
- G395H: see NIRSpec
- G395M: see NIRSpec
- GBP: see Gaia
- GR
- G band: band of visible light around 5100 angstroms
- GRP: see Gaia
- GRVS: see Gaia
- Gabbard diagram (Gabbard plot): plot showing apogee-perigee range of select orbiting debris
- Gabbard plot: plot showing apogee-perigee range of select orbiting debris
- GADGET
- GADGET-2: an n-body/SPH simulation computer program
- GADGET-1
- GADGET-2: an n-body/SPH simulation computer program
- GADGET-2: an n-body/SPH simulation computer program
- GADGET-3
- GADGET-4
- GADGET-2: an n-body/SPH simulation computer program
- Gaia: astrometry survey satellite launched in 2013
- Gaia Celestial Reference Frame: celestial reference frame based upon Gaia data
- Gaia Celestial Reference Frame 3 (Gaia Celestial Reference Frame): celestial reference frame based upon Gaia data
- Gaia Data Release 1: see Gaia
- Gaia Data Release 2: see Gaia
- Gaia Data Release 3: see Gaia
- Gaia DR1: see Gaia
- Gaia DR2: see Gaia
- Gaia DR3: see Gaia
- Gaia Early Data Release 3: see Gaia
- Gaia EDR3: see Gaia
- Gaia Enceladus: galaxy that merged with the Milky Way
- Gaia G: see Gaia
- Gaia Sausage (Gaia Enceladus): galaxy that merged with the Milky Way
- Gaia-CRF: see Gaia Celestial Reference Frame
- Gaia-CRF2: see Gaia Celestial Reference Frame
- Gaia-CRF3 (Gaia Celestial Reference Frame): celestial reference frame based upon Gaia data
- Gaia-ESO Survey: see Gaia
- gaia-kepler.fun: website with Gaia data on Kepler target stars
- gaia-kepler.fun crossmatch database (gaia-kepler.fun): website with Gaia data on Kepler target stars
- GaiaHub: software to extract proper motions form Gaia and HST data
- GaiaNIR: concept for a Gaia follow-on including NIR astrometry
- GAL: see double star designation
- Gal: gravimetry unit of the effect of a planet's gravity
- admittance: effect of atmospheric pressure on gravity
- gal (Gal): gravimetry unit of the effect of a planet's gravity
- GALA: see JUICE
- Gala: galaxy-formation and evolution software package
- GALACSI: see European Southern Observatory Very Large Telescope
- Galactic / Extragalactic ULDB Spectroscopic Terahertz Observatory (GUSTO): balloon-borne 0.9-m far-infrared telescope
- Galactic All-sky Survey: HI survey of the Milky Way
- Galactic and Extragalactic All-sky MWA Extended survey: see GLEAM
- Galactic and Extragalactic All-sky MWA survey (GLEAM): MWA radio survey of the southern sky
- galactic anticenter: direction opposite the galactic center
- galactic archaeology: study of galaxy characteristics that reveal their past
- Galactic Archaeology with HERMES (GALAH): survey of Milky Way with an emphasis on old structures
- Galactic Arecibo L-Band Feed Array HI Survey: see Galactic All-sky Survey
- Galactic ASKAP Spectral Line Survey-HI: see Australian Square Kilometre Array Pathfinder
- Galactic ASKAP Spectral Line Survey-OH: see Australian Square Kilometre Array Pathfinder
- galactic astronomy: astronomy confined to the Milky Way
- galactic binary: system of two object co-orbiting within the Milky Way
- galactic bulge: bulge of many stars in the center of the Milky Way
- galactic bulge: see bulge
- galactic center: region at the middle of the Milky Way
- MicroFUN: observers following up on microlensing events in the galactic bulge
- Galactic Bulge Time Domain Survey: see Roman Space Telescope
- galactic center: region at the middle of the Milky Way
- galactic center magnetar (SGR J1745-2900): magnetar orbiting the Milky Way SMBH
- galactic cirrus (infrared cirrus): cirrus-cloud-like infrared emissions from dust, etc.
- galactic cluster (open cluster): group of stars within a galaxy apparently formed by a single cloud
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- galactic coordinate system: celestial coordinate system system based upon the galactic plane
- galactic coordinates
- galactic north: determination of the more northern direction of the Milky Way's axis
- galactic core (galactic center): region at the middle of the Milky Way
- galactic corona: see corona
- galactic corona: see galactic halo
- galactic corona: see supershell
- galactic cosmic rays: see cosmic rays
- galactic disc (galactic disk): the "disk" portion of a disk galaxy
- galactic disk: the "disk" portion of a disk galaxy
- galactic electron density: density of electrons in the ISM
- Galactic Emission Mapping: radio sky survey
- galactic equator (galactic plane): plane in which the stars of the Milky Way reside
- galactic filament (galaxy filament): thread-like formations of galaxies, 50 to 80 megaparsecs
- galactic fountain: see supershell
- galactic gamma-ray background: see gamma rays
- galactic habitable zone: see habitable zone
- galactic halo: spherical region around a galaxy with gas, dark matter, etc.
- stellar halo: the lesser number of nearby stars surrounding a galaxy
- galactic jet: see jet
- galactic latitude: see galactic coordinate system
- galactic longitude: see galactic coordinate system
- galactic magnetic field: see magnetic field
- galactic main sequence (galaxy main sequence): relation between galaxies' star formation and stellar mass
- galactic north: determination of the more northern direction of the Milky Way's axis
- galactic north pole (galactic north): determination of the more northern direction of the Milky Way's axis
- galactic nucleus (stellar nucleus): group of many stars at the center of a galaxy
- Galactic O Star Catalog: 2000s catalog of O-type stars
- Galactic O Star Spectral Survey: see Galactic O Star Catalog
- galactic period: see Milky Way
- galactic plane: plane in which the stars of the Milky Way reside
- Galactic Plane Exoplanet Survey (GPX): amateur effort to uncover exoplanets within the galactic plane
- Galactic Plane Infrared Polarization Survey
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- galactic planetary nebulae
- galactic poles: see galactic north
- galactic poles: see galactic plane
- galactic sheet: see galaxy filament
- galactic south: see galactic north
- galactic south pole: see galactic north
- galactic stellar nucleus (stellar nucleus): group of many stars at the center of a galaxy
- galactic superwind (galactic wind): wind of charged particles out of some galaxies
- galactic tide: effect of one galaxy's gravity, such as on another galaxy
- tidal force: effect of a third body on the gravitational force between two bodies
- galactic void (void): empty spaces between large scale structures
- galactic wind: wind of charged particles out of some galaxies
- galactic worm: high density streak of HI perpendicular to galactic plane
- galactic year: see Milky Way
- GALAH: survey of Milky Way with an emphasis on old structures
- Galatea: see shepherd moon
- galaxies
- 2dF Galaxy Redshift Survey: imaging survey of 300,000 extragalactic objects
- 2dF-SDSS LRG and QSO survey: spectroscopic survey of distant galaxies
- 2MASS Photometric Redshift Catalog: galaxy redshifts from 2MASS
- 3D-HST: near-infrared survey of 100,000 galaxies by HST
- 6dF Galaxy Survey: UKST survey of galaxies in the southern sky
- active galactic nucleus: central region of a galaxy with extremely high luminosity
- AEGIS: early 2000s survey study of distant galaxies
- ALFALFA: HI survey of many galaxies
- ALMACAL: galaxy survey using ALMA calibration observations
- APM Galaxy Survey: 1990s survey of galaxies in southern sky
- Arakelian Catalog: 1970s list of small/bright galaxies
- Arecibo General Catalog: catalog of galaxies to support ALFALFA surveys
- Arp-Madore Catalog of Southern Peculiar Galaxies: 1970s-1980s catalog from the UK Schmidt Survey
- Asiago Supernova Catalog: catalog of known supernovae and their galaxies
- Atlas 3D: survey of local galaxies
- Atlas of Peculiar Galaxies: 1960s catalog-book with photos
- bar: central feature of some spiral galaxies
- BDF: field used in search for distant galaxies
- BigBOSS: BOSS survey follow-on
- binary SMBH: co-orbiting supermassive black holes
- broad line region: AGN region producing broader lines
- bulge: denser group of stars within a larger group
- Butcher-Oemler effect: observation of more blue galaxies at z > 0.3
- Caldwell Catalog: small catalog for amateur astronomers as an adjunct to the Messier Catalog
- CALIFA: spectroscopic map of 600 galaxies
- Canada-France Redshift Survey: 1990s survey of galaxies to z = 1 to find associations of redshift to characteristics
- CARMA EDGE: survey CO-mapping galaxies
- Catalog of Galaxies and Clusters of Galaxies: list of galaxies/clusters assembled in 1960s
- Catalogue of Interacting Galaxies: begun in the 1950s
- CfA Redshift Survey: 1970s-1990s surveys of galaxy redshifts
- CFHTLS: surveys of transients and stars
- Chandra Deep Field North: X-ray deep survey encompassing HDF region
- Chandra Deep Field South: X-ray deep survey encompassing HDF-South region
- circumgalactic medium: gas surrounding a galaxy
- cold gas: gas cool enough to form galaxies and stars
- COLD GASS: survey of CO in nearby large galaxies
- color-color diagram: means of comparing characteristics of stars
- color-magnitude diagram: graph plotting color index to magnitude
- conditional luminosity function: function characterizing luminosity of galaxies with a given halo mass
- conditional stellar mass function: function characterizing galaxies within a halo of a given mass
- Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey: early-universe survey by HST
- cosmic web: hypothesized structure of the dark matter throughout the universe
- Council of Giants: twelve large galaxies surrounding the Local Group
- dark matter: matter in galaxies and galaxy clusters suggested by their gravity
- dark matter halo: hypothetical dark matter throughout and surrounding a galaxy
- David Dunlap Observatory Catalog: catalog of dwarf galaxies
- de Vaucouleurs' profile: relation between elliptical galaxy surface brightness and distance from center
- DECaLS: survey imaging part of SDSS footprint with DECam
- deep field: survey field subject to lengthy observation to identify distant galaxies
- Deep Lens Survey: investigating mass distribution of the universe
- Deep Multicolor Survey: 1990s optical and infrared deep survey
- deep survey: survey using lengthy observation to identify distant galaxies
- DEEP2: redshift survey of 60,000 galaxies
- disk: rotating disk-shaped object such as disk galaxy or circumstellar disk
- dropout: means of identifying distant galaxies
- Duus-Newell catalog: list of southern galaxies/clusters assembled in 1970s
- dwarf galaxy classification: terms for of dwarf galaxy types
- Dwingeloo Obscured Galaxy Survey: radio survey of ZOA for 21-cm lines indicating galaxies
- effective radius: radius of a galaxy within which 1/2 the light is emitted
- escape fraction: fraction of ionizing photons escaping a body
- ESO Nearby Abell Cluster Survey: 1990s spectroscopy and photometry survey of galaxy clusters
- Extended Chandra Deep Field-South Survey: 1100 square arcminute X-ray survey
- Extended Groth Strip: region of sky searched for distant galaxies
- extragalactic astronomy: astronomy of other galaxies, galaxy clusters, AGNs, quasars, etc.
- Extragalactic Distance Database: online database of distance-related measures of galaxies
- F4: FRB followup project
- Faber-Jackson relation: relation between elliptical galaxy luminosity and stellar velocity dispersion
- Faint Infrared Grism Survey: survey to identify redshift of distant galaxies
- Fairall Galaxy List: 1977 list of galaxies with bright nuclei
- Fanaroff-Riley classification: a classification of the radio characteristics of radio sources
- field: adjective meaning "in this field of view but unrelated"
- FIRE Simulations: high resolution simulation of galaxies
- fossil group: apparent remnant of a galaxy group
- FourStar Galaxy Evolution Survey: infrared deep-survey to detect galaxies
- Freeman's law: all spiral galaxy's have the same central surface brightness
- fundamental plane: three-way relation between elliptical galaxy characteristics
- Gala: galaxy-formation and evolution software package
- galactic archaeology: study of galaxy characteristics that reveal their past
- galactic disk: the "disk" portion of a disk galaxy
- galactic electron density: density of electrons in the ISM
- galactic halo: spherical region around a galaxy with gas, dark matter, etc.
- galactic tide: effect of one galaxy's gravity, such as on another galaxy
- galactic wind: wind of charged particles out of some galaxies
- galaxy age determination: methods of estimating a galaxy's age
- galaxy bias: degree to which galaxy density fails to correspond to dark matter density
- galaxy classification: morphological classification of galaxies
- galaxy cloud: substructure of a supercluster
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- galaxy environment: density and character of galaxies surroundings
- Galaxy Evolution from Morphology and Spectral energy distributions: HST survey of galaxies with z in the range 0.2 to 1.2
- galaxy filament: thread-like formations of galaxies, 50 to 80 megaparsecs
- galaxy formation: modeled as collapsing clouds
- galaxy group: group of fifty or fewer gravitationally-bound Milky-Way-sized galaxies
- galaxy harassment: frequent occurrences of small galaxies passing close to a galaxy
- galaxy interaction: the effects of galaxies being near each other
- galaxy main sequence: relation between galaxies' star formation and stellar mass
- galaxy merger: combination of galaxies upon collision
- galaxy power spectrum: a power spectrum describing the occurrence of galaxies in space
- galaxy SED: SED of a galaxy, sometimes synthesized from photometric surveys
- galaxy strangulation: galaxy star formation stopped by a lack of incoming gas
- galaxy subgroup: a major galaxy and its satellites
- Galaxy Zoo: crowdsourcing website to identify galaxy types from surveys
- Galaxy Zoo 2: crowd-sourced classification of hundreds of thousands of galaxies
- GalDNA: code to estimate chemical abundances from galaxy emission lines
- GALEX Arecibo SDSS Survey: HI survey of many galaxies
- GAMA: galaxy spectroscopy survey to roughly 1 Mpc
- Gini/M20: an automatable method of detecting whether a galaxy has recently merged
- GLADE: list of galaxies likely to host GW events
- GLARE: project to search for distant star-forming galaxies
- globular cluster luminosity function: distribution of brightness of globular clusters
- GOALS: across-spectrum observation of 200 LIRGs
- GOODS NICMOS Survey: survey with HST NICMOS instrument of galaxies in GOODS fields
- Gravitational Wave Galaxy Catalogue: list of probable galaxies for GW detections
- Great Debate: historical debate regarding the nature of galaxies
- Groth Strip: region of sky in early HST survey
- halo abundance matching: method of comparing observed galaxies with cosmology models
- Hawaii K-band Galaxy Survey: near-infrared survey of a selection of fields
- Herschel Stripe 82 Survey: 70 square-degree survey of galaxies redshifted 1.8 to 3.5
- HI gas mass: mass of an object's atomic hydrogen
- hierarchical assembly of galaxies: development of large galaxies by combining small ones
- Holmberg radius: a measure of size of galaxy based on surface brightness
- host galaxy: galaxy associated with a particular object or transient
- Hubble Deep Field: highly-detailed image of a small region of the sky taken with HST
- Hubble Deep Field South: small region of the southern sky explored with HST
- Hubble diagram: diagram comparing redshift with distance
- Hubble Ultra-Deep Field: extremely detailed HST image of a small region of space
- inside-out growth: tendency of galaxy star formation to spread from the center
- intergalactic medium: matter between galaxies
- interstellar radiation field: EMR throughout the "empty" space of a galaxy
- ITEP-SAI Supernova Light Curve Catalogue: online catalog
- Jeans anisotropic modeling: method of determining stellar kinematics of early type galaxies
- Jeans equations: relating the motion of stars to the surrounding gravitational field
- JINGLE: survey of dust and gas in galaxies
- JWST Extragalactic Mock Catalog: mock catalog of distant infrared galaxies
- Kepler-Swift Active Galaxies and Stars Survey: X-ray/UV survey of objects within the Kepler field
- kinemetry: method of determining galaxy kinematics through photometry
- Kiso Survey of Ultraviolet Excess Galaxies: 1980 Japanese survey
- KMOS3D: survey of galaxies before to after peak star formation
- Kormendy Relation: relation between elliptical galaxy luminosity surface brightness
- Las Campanas Redshift Survey: 1990s survey of galaxies out to z = 0.2
- LEDA: galaxy database with observation data
- Limber approximation: formula approximating the density of galaxies in some direction
- LINER: galaxy nucleus emitting spectral lines for ionized and neutral atoms
- LOSVD: line-of-sight velocity distribution
- luminosity function: function giving number of stars or galaxies at different luminosities
- Lyman break: abrupt change in galaxy spectrum at the Lyman series wavelength limit
- M-sigma relation: relation between galaxy center's velocity dispersion and SMBH mass
- Magellanic Analog Dwarf Companions And Stellar Halos: Subaru survey for dwarf glaxies beyond the Local Group
- Magellanic Clouds: two nearby galaxies
- mass transport: transfer of mass from one part of a body/disk to another
- Medium Deep Survey: survey to find galaxies in HST WFPC2 images
- Meier paradox: mysterious decline in number of radio galaxy jets
- Messier Catalog: catalog of astronomical objects to avoid when looking for comets
- metallicity gradient: the degree to which metallicity changes across a galaxy
- MIGHTEE: radio survey of four established deep fields
- Milky Way subgroup: the Milky Way and its satellites
- Millennium Galaxy Catalogue: 2000s catalog of 10,000 galaxies
- MOJAVE: program to monitor AGN jet radio brightness and polarization
- molecular cloud turbulence: observed turbulence in molecular clouds
- MORA: high resolution 2-mm survey of a portion of the COSMOS field
- Morgan classification: classification of galaxies by stellar spectrum and morphology
- Morphological Catalogue of Galaxies: 1960s catalog from Palomar plates
- morphology: form and structure
- morphology-density relation: a galaxy is more likely to be elliptical if surrounded by galaxies
- moving group: observed group of stars with similar motion
- Munich Near-Infrared Cluster Survey: 1990s-2000s galaxy cluster survey
- narrow line region: AGN region producing narrower lines
- NASA/IPAC Extragalactic Database: a database of galaxies and other objects outside the Milky Way
- New General Catalogue: 1888 catalog of galaxies, star clusters, and other nebulae
- NOAO Deep Wide-field Survey: survey investigating large scale structure of the universe
- OB association: stellar association including O and/or early B class stars
- Ogle Galaxy Catalog: catalog of luminous galaxies
- open cluster: group of stars within a galaxy apparently formed by a single cloud
- Palomar high-redshift quasar surveys: 1980s Hale-telescope quasar searches using new technology
- Parkes HI Zone of Avoidance Survey: radio survey to identify galaxies hidden by the zone of avoidance
- PCA analysis: an automatable method of determining galaxy morphology
- peak star-formation epoch: around 10 billion years ago when star formation peaked
- PHANGS: set of surveys of nearby galaxies
- planetary nebula luminosity function: model used in distance estimation
- Polar-ring Catalog: 1990 catalog of polar-ring galaxies
- Press-Schechter formalism: cosmological model of how structures form from fluctuations
- PRIMUS: spectrographic survey of galaxies out to redshift 1
- Principal Galaxies Catalog: modern catalog of more than 70k galaxies
- protogalaxy: gas cloud forming a galaxy
- pseudobulge: like a galaxy bulge only flatter
- quasar: distant, bright object that appears something like a star
- radial mixing: tendency of disk galaxy stars to change their orbital radius
- Radio Galaxy Zoo: crowd-sourced classification of radio galaxies
- RASS/Green Bank Catalog: combined list of radio galaxies from Rosat and Green Bank surveys
- REBELS: survey of star-forming galaxies during the reionization
- red and dead: description of a galaxy with old stars and no star formation
- Reference Catalogue of Bright Galaxies: series of catalogs of nearby galaxies
- REFINE: catalog of high-redshift galaxies
- RESOLVE: galaxy and gas survey limited to 65-100 Mpc
- reverberation mapping: technique for measuring the size of SMBHs
- Roma-BZCAT: 2008 catalog of blazars
- rotation curve: function mapping distance from galaxy center to orbital speed of stars
- Sérsic profile: model of the relative surface brightness across a galaxy
- Scott effect: bias toward finding clusters that have bright galaxies
- Second Byurakan Survey: 1970s-1990s survey of galaxies and quasars
- Shapley-Ames Catalog: 1932 catalog of contemporary data on 1249 galaxies
- SHARDS: GTC survey in GOODS-N field for quenched galaxies at z = 1 to 2.3
- SIMBA: galaxy formation simulation code
- SINS: near-infrared study of distant luminous galaxies
- Southern Sky Redshift Survey: 1980s/1990s redshift survey of southern galaxies
- spiral arm: long, winding visible structure within a spiral galaxy
- spiral density wave: spiral structure that can form in disks
- Spitzer Extended Deep Survey: survey of galaxy mass and black holes through life of the universe
- Spitzer HETDEX Exploratory Large Area Survey: Spitzer-based survey of galaxies
- star formation feedback: mechanisms whereby star formation regulates its own rate
- star formation history: star formation rate as a function of time
- star formation rate: rate at which material such as gas is turned into stars
- star-formation rate stellar-mass ratio: ratio between a galaxy's stellar mass and its SF rate
- STARSMOG: survey of dust in galaxies
- stellar association: like a large open cluster but even less tightly bound
- stellar cluster: group of stars apparently formed by a single cloud
- stellar dynamics: stars' gravitational interaction
- stellar halo: the lesser number of nearby stars surrounding a galaxy
- stellar nucleus: group of many stars at the center of a galaxy
- stellar overdensity: portion of galactic halo with more stars than normal
- stellar population synthesis: using spectral characteristics of galaxies to characterize their stellar populations
- Stephan's Quintet: five galaxies grouped in the sky
- structure formation: formation of dark matter halos, galaxy clusters, and galaxies
- Subaru Deep Field: survey of a small region of the sky using the Subaru telescope
- Subaru XMM-Newton Deep Survey: survey using the Subaru telescope and XMM-Newton
- submillimeter galaxy designator: designation system of submillimeter galaxies
- SuperCOSMOS Sky Survey: survey of stars and galaxies from legacy plates
- supermassive black hole: black hole with a mass of millions to billions of solar masses
- surface brightness fluctuation: apparent indication of an elliptical galaxy's distance
- surface brightness profile: curve of a galaxy's brightness from center to edge
- systemic velocity: average velocity of grouped objects, such as a galaxy
- T association: stellar association with T-Tauri stars
- The Survey for Ionization in Neutral Gas Galaxies: survey of HI in galaxies found through the H-alpha line
- thick disk: disk-shaped set of older stars within the Milky Way
- thin disk: disk-shaped set of younger stars within the Milky Way
- tidal arm: arm of gas and potentially stars leading from a galaxy
- TiNy Titans: study of dwarf galaxy pairs
- tip of the red-giant branch: standard candle consisting of the brightest RGB stars
- Toomre sequence: model relating galaxy mergers to observation
- Tully-Fisher relation: relation between spiral galaxy luminosity and line width
- Two Micron All-sky Survey: near-infrared survey of both hemispheres
- Uppsala General Catalogue: 1973 catalog of galaxies visible from northern hemisphere
- UVCANDELS: UV survey of CANDELS fields
- UVJ diagram: diagram to identify star formation in distant galaxies
- van den Bergh galaxy classification: galaxy classification variant including luminosity
- VIMOS Public Extragalactic Redshift Survey: spectrographic redshift survey of 80,000 galaxies
- Virgo Cluster Catalog: 1980s catalog of 2000 galaxies
- warp: bend in the otherwise-flat disk of a galaxy
- WHISP: 1990s/2000s radio survey mapping HI density and velocity
- WiggleZ: survey aimed at mapping dark energy
- WINGS: all-sky survey investigating known galaxy clusters
- WISE x SuperCOSMOS photometric redshift catalog: catalog of distant galaxies in WISE and SuperCOSMOS
- WISeREP: interactive catalog of supernovae
- X-ray luminosity function: maps X-ray luminosities to count of such sources
- X-SHOOTER Lyman α survey at z = 2: survey of Lyman-α sources
- Galaxies with High Surface Brightness (Arakelian Catalog): 1970s list of small/bright galaxies
- GALAXY: see SuperCOSMOS Sky Survey
- galaxy: gravitationally-bound group of stars
- galaxy age determination: methods of estimating a galaxy's age
- Galaxy and Mass Assembly Survey (GAMA): galaxy spectroscopy survey to roughly 1 Mpc
- galaxy bar (bar): central feature of some spiral galaxies
- galaxy bias: degree to which galaxy density fails to correspond to dark matter density
- galaxy bimodality: see galaxy
- galaxy bulge: see bulge
- galaxy cannibalism: see galaxy merger
- galaxy classification: morphological classification of galaxies
- galaxy cloud: substructure of a supercluster
- galaxy cluster: large group of galaxies gravitationally-bound to the group
- galaxy cluster merger
- galaxy clusters
- galaxy collision
- galactic tide: effect of one galaxy's gravity, such as on another galaxy
- galaxy color-magnitude diagram
- galaxy diagram
- galaxy environment: density and character of galaxies surroundings
- Galaxy Evolution Explorer: observatory-satellite with 50-cm ultraviolet telescope
- Galaxy Evolution from Morphology and Spectral energy distributions: HST survey of galaxies with z in the range 0.2 to 1.2
- galaxy feedback: see star formation feedback
- galaxy filament: thread-like formations of galaxies, 50 to 80 megaparsecs
- galaxy formation: modeled as collapsing clouds
- galaxy group: group of fifty or fewer gravitationally-bound Milky-Way-sized galaxies
- galaxy groups
- galaxy harassment: frequent occurrences of small galaxies passing close to a galaxy
- galaxy interaction: the effects of galaxies being near each other
- galactic tide: effect of one galaxy's gravity, such as on another galaxy
- galaxy harassment: frequent occurrences of small galaxies passing close to a galaxy
- tidal tail: string of mass ejected by a tidal forces in a neutron star merger
- Galaxy List for the Advanced Detector Era (GLADE): list of galaxies likely to host GW events
- galaxy luminosity class
- galaxy luminosity function: see luminosity function
- galaxy main sequence: relation between galaxies' star formation and stellar mass
- galaxy merger: combination of galaxies upon collision
- galactic tide: effect of one galaxy's gravity, such as on another galaxy
- galaxy merger mass ratio: see galaxy merger
- galaxy merger timescale: see galaxy merger
- galaxy morphology: see galaxy classification
- galaxy nucleus
- galaxy power spectrum: a power spectrum describing the occurrence of galaxies in space
- galaxy quenching: see quenched galaxy
- galaxy rotation curve (rotation curve): function mapping distance from galaxy center to orbital speed of stars
- galaxy SED: SED of a galaxy, sometimes synthesized from photometric surveys
- galaxy sheet: see galaxy filament
- supercluster: cluster of galaxy clusters
- void: empty spaces between large scale structures
- galaxy spectral energy distribution (galaxy SED): SED of a galaxy, sometimes synthesized from photometric surveys
- galaxy strangulation: galaxy star formation stopped by a lack of incoming gas
- galaxy subgroup: a major galaxy and its satellites
- galaxy subgroup: see galaxy group
- galaxy supercluster
- galaxy type: see galaxy classification
- galaxy wall: see galaxy filament
- supercluster: cluster of galaxy clusters
- void: empty spaces between large scale structures
- galaxy warp (warp): bend in the otherwise-flat disk of a galaxy
- Galaxy Zoo: crowdsourcing website to identify galaxy types from surveys
- Galaxy Zoo 2: crowd-sourced classification of hundreds of thousands of galaxies
- Planet Hunters: crowdsourcing website to identify galaxy types from surveys
- Radio Galaxy Zoo: crowd-sourced classification of radio galaxies
- Galaxy Zoo 2: crowd-sourced classification of hundreds of thousands of galaxies
- GalDNA: code to estimate chemical abundances from galaxy emission lines
- Gale Crater: Curiosity rover landing site on Mars
- Gale Crater: see Mars Science Laboratory
- Galerkin method
- GALEX (Galaxy Evolution Explorer): observatory-satellite with 50-cm ultraviolet telescope
- GALEX Arecibo SDSS Survey: HI survey of many galaxies
- COLD GASS: survey of CO in nearby large galaxies
- GALEX ASC: see Galaxy Evolution Explorer
- GALFA-Dw: see rare designator prefixes
- GALFA-HI: see Galactic All-sky Survey
- GALFORM: semi-analytic galaxy formation model
- Galilean frame of reference (inertial reference frame): frame of reference where no force means no acceleration
- Galilean Moons: see Jupiter
- Callisto: well-known Jupiter moon
- Europa: well-known Jupiter moon
- Ganymede: well-known Jupiter moon
- Io: well-known Jupiter moon
- moon: a planet's natural satellite, such as Earth's
- Galilean relativity: see relativity
- Galilean transform: see relativity
- Galilean transformation: see Lorentz transformation
- GALILEO: see Parkes Observatory
- Galileo: circa 1990s space mission to Jupiter
- Galileo (Gal): gravimetry unit of the effect of a planet's gravity
- Ganymede: well-known Jupiter moon
- Io: well-known Jupiter moon
- Galileo Europa Mission: see Galileo
- Galileo Millennium Mission: see Galileo
- Galileo National Telescope (Telescopio Nazionale Galileo): 3.58 m telescope in Canary Islands
- Galileo Observatory: 1960s-1970s infrared observatory aircraft
- GalMC: see spectral energy distribution
- GAMA: galaxy spectroscopy survey to roughly 1 Mpc
- Gamma Cassiopeiae variable: see variable star
- shell star: type of star with broad and narrow absorption lines
- gamma decay: see radioactive decay
- Gamma Leporis A
- F-type star: spectral class of star a bit hotter than then Sun
- Gamma Ray Astronomy PeV Energies phase-3 (GRAPES-3): Cherenkov telescope at Ooty, India
- Gamma Ray Burst Counterpart Search Experiment: see ROTSE
- gamma ray photon
- gamma rays: electromagnetic radiation, wavelength 10 picometers and less
- gamma-ray astronomy: see gamma rays
- gamma-ray burst: short flash of gamma rays apparently from outside our galaxy
- gamma-ray burst: short flash of gamma rays apparently from outside our galaxy
- Gamma-ray Burst Coordinates Network: system to distribute notifications of GRBs
- gamma-ray burst progenitor: see gamma-ray burst
- gamma-ray burst source: see gamma-ray burst
- gamma-ray bursts
- Gamma-ray Large Area Space Telescope (Fermi): satellite for studying gamma rays
- gamma-ray source: see gamma rays
- gamma-ray source: see source
- radio source: astronomical object producing observable radio
- Gamow Explorer: proposal for GRB space mission
- Gamow factor: see Gamow peak
- Gamow peak: relative speed most likely to cause atoms to fuse within a gas
- Gamow tunneling factor: see Gamow peak
- Gamow window (Gamow peak): relative speed most likely to cause atoms to fuse within a gas
- Ganymede: well-known Jupiter moon
- gap (disk gap): empty radius-range within a disk separating it into rings
- gap transient (intermediate luminosity optical transient): visible-light transient a bit brighter than a nova
- GAS: see Ulysses
- gas
- gas blowout: see starburst galaxy
- gas cloud: see interstellar medium
- gas constant
- gas disk migration: see planetary migration
- gas dwarf (mini-Neptune): planet with characteristics a bit like Earth but more like Neptune
- gas dwarf: see gas planet
- gas dwarf: see super-Earth
- gas electron multiplier: see gas pixel detector
- gas excitation: see atomic excitation
- gas extinction: see extinction
- gas flow: dynamics of gas, plasma, i.e., compressible fluids
- gas fraction: fraction of a galaxy or cluster consisting of gas
- gas fraction estimation: methods of estimating various amounts of gas in galaxies
- gas giant: large planet made largely of gas
- gas mass fraction (gas fraction): fraction of a galaxy or cluster consisting of gas
- gas pixel detector: type of X-ray imager sensitive to polarization
- gas planet: planet made largely of gas
- gas streamer: stream of gas
- gas tail: see comet
- gas torus: see Io
- gas-to-core ratio: see gas planet
- gas-to-dust ratio: mass ratio of gas to dust, such as within a SF region
- gaseous corona: see supershell
- gaseous envelope: see atmosphere
- GASKAP-HI: see Australian Square Kilometre Array Pathfinder
- GASKAP-OH: see Australian Square Kilometre Array Pathfinder
- Gasoline: an SPH code
- Gasoline2: see Gasoline
- GASP (Guide Star Astrometric Support Package): software to assist in using guide stars for HST observations
- GASS (GALEX Arecibo SDSS Survey): HI survey of many galaxies
- GASS (Galactic All-sky Survey): HI survey of the Milky Way
- GAT: see rare designator prefixes
- Gattini-IR: IR transient survey telescope
- gauge boson
- Gaunt factor
- gauss: measurement of magnetic field β
- Gauss's law
- Gaussian: see Gaussian function
- Gaussian distribution: see Gaussian function
- photon noise: variation in light measurement due to its quantum nature
- Gaussian function: function producing the bell curve
- Gaussian profile: see Gaussian function
- Doppler broadening: broadening of spectral lines due to movement of the sources of photons
- Gaussian system: see CGS
- Gaussian units: see CGS
- GB (Green Bank Telescope): West Virginia large radio telescope
- GB: see gamma-ray burst
- GB-BL: see Breakthrough Listen
- GB1: see Green Bank 6-cm Radio Source Catalog
- GB2: see Green Bank 6-cm Radio Source Catalog
- GB3: see Green Bank 6-cm Radio Source Catalog
- GB300 (Green Bank 300ft Telescope): former large radio telescope at Green Bank
- GB6 (Green Bank 6-cm Radio Source Catalog): catalog of from 1980s northern-hemisphere radio survey
- GBD: see Ginga
- GBM: see Fermi
- GBO (Green Bank Observatory): radio observatory in West Virginia including GBT
- GBS: see gamma-ray burst
- GBT (Green Bank Telescope): West Virginia large radio telescope
- GC (Boss General Catalog): 1936 catalog of 30,000 stars
- GC (globular cluster): spherical group of stars orbiting a galaxy
- GC: see Green Bank 6-cm Radio Source Catalog
- GC: see New General Catalogue
- GC bimodality: see globular cluster
- GC magnetar (SGR J1745-2900): magnetar orbiting the Milky Way SMBH
- GC system: see globular cluster
- GC/MS: see Cassini
- GCAS: see variable star
- shell star: type of star with broad and narrow absorption lines
- GCC: see globular cluster
- GCGSS: see rare designator prefixes
- GCIRS: see rare designator prefixes
- GCLF (globular cluster luminosity function): distribution of brightness of globular clusters
- GCM (general circulation model): climate model of a planet's atmosphere or ocean
- GCM: see rare designator prefixes
- GCMS: see Cassini
- GCN (Gamma-ray Burst Coordinates Network): system to distribute notifications of GRBs
- GCR: see cosmic rays
- GCR: see gas planet
- GCRT: galactic center radio transient
- GCRV (General Catalogue of Stellar Radial Velocities): 1950s century catalog of 15000 stars with their radial velocities
- GCS (galactic coordinate system): celestial coordinate system system based upon the galactic plane
- GCS: see UKIDSS
- GCS: see rare designator prefixes
- GCSS: see rare designator prefixes
- GCTP (General Catalogue of Trigonometric Parallaxes): 1950s catalog of stars with parallax measures
- GCVS (General Catalogue of Variable Stars): 20th/21st century catalog of 58000 variable stars
- GD: see Lowell Proper Motion Survey
- GD-1: stellar stream formed by globular cluster
- GDR (gas-to-dust ratio): mass ratio of gas to dust, such as within a SF region
- GDS: see Neptune
- GDS-89: see Neptune
- GDSCC: see NASA Deep Space Network
- GECAM
- GECAM-C: see Satech-01
- Geiger counter
- Geiger mode: see Geiger-avalanche photodiode
- Geiger-avalanche photodiode: type of solid state photon sensor
- Geiger-Müller tube
- GEM (Galactic Emission Mapping): radio sky survey
- GEM: see Galileo
- GEM: see Giotto
- GEM: see gas pixel detector
- GEM: see gravitomagnetic field
- GEM Telescope
- Gemini
- RESOLVE: galaxy and gas survey limited to 65-100 Mpc
- Gemini Camera: see Shane Telescope
- Gemini Lyman Alpha at Reionisation Era (GLARE): project to search for distant star-forming galaxies
- Gemini North: see Gemini Observatory
- Gemini Observatory: pair of telescopes in Hawaii and Chile
- Gemini Planet Imager: infrared instrument to overcome signal noise imaging exoplanets
- Gemini Planet Imager: see Gemini Observatory
- Gemini Planet Imager 2.0: see Gemini Planet Imager
- Gemini South: see Gemini Observatory
- Gemini-South
- GLARE: project to search for distant star-forming galaxies
- GEMS (Galaxy Evolution from Morphology and Spectral energy distributions): HST survey of galaxies with z in the range 0.2 to 1.2
- GEMS (Group Evolution Multiwavelength Study): survey of galaxy groups
- GeMS: see Gemini Observatory
- GEMSS (Global Exoplanet M-dwarf Search-Survey): a search for exoplanets around m-dwarf stars
- General Automatic Luminosity And X-Y: see SuperCOSMOS Sky Survey
- General Catalogue of 1290 Double Stars: see Burnham Double Star Catalogue
- General Catalogue of 33,342 Stars (Boss General Catalog): 1936 catalog of 30,000 stars
- General Catalogue of Double Stars Within 121° of the North Pole (Burnham Double Star Catalogue): 1906 catalog with multiple star systems and non-orbiting double stars
- General Catalogue of Nebulae and Clusters of Stars: see New General Catalogue
- General Catalogue of Stellar Radial Velocities: 1950s century catalog of 15000 stars with their radial velocities
- General Catalogue of Trigonometric Parallaxes: 1950s catalog of stars with parallax measures
- General Catalogue of Trigonometric Stellar Parallaxes (General Catalogue of Trigonometric Parallaxes): 1950s catalog of stars with parallax measures
- General Catalogue of Variable Stars: 20th/21st century catalog of 58000 variable stars
- general circulation model: climate model of a planet's atmosphere or ocean
- general precession (precession of the equinoxes): Earth axial precession with a 26000-year cycle
- general precession: see precession of the equinoxes
- general relativistic effects
- general relativity: formula relating gravity, space, time, and mass
- Big Bang: theoretical event when the universe expanded from a point
- bigravity: modifications to GR defining two metrics
- effective field theory: type of useful simplification of a field theory
- f(R) gravity: class of modifications to general relativity
- Lambda-CDM model: Big-Bang cosmological model with a cosmological constant and cold dark matter
- LARES: satellite to test a general relativity effect
- metric: mathematical generalization of the concept of distance
- scalar-tensor gravity: GR-like gravity that incorporates a scalar field
- Shapiro delay: EMR delay due to passing near massive object
- wCDM: Big-Bang cosmological model with constant cosmological equation of state
- worldline: path of an object through space and time
- general-relativistic MHD: see magnetohydrodynamics
- Generalized NFW profile: see Navarro-Frenk-White profile
- Genesis: NASA spacecraft that returned solar wind particles
- GEO project: see GEO600
- GEO600: ground-based gravitational-wave detector in Germany
- Geocentric Coordinate Time: see Terrestrial Time
- geocentric gravitational constant: see standard gravitational parameter
- geocentric system: see heliocentric system
- geochemistry: the chemistry of the Earth, planets, and moons
- geodesic: equivalent to a straight line within curved space
- geodetic effect: see Gravity Probe B
- GEODM: see Cryogenic Dark Matter Search
- GEODSS (Ground-Base Electro-Optical Deep Space Surveillance): initiative to track artificial spacecraft including space junk
- geodynamo: see dynamo
- geology
- basalt: an igneous rock type that shows rapid cooling
- bathymetry: study and measurement of sea depths
- bulk silicate earth: the early overall composition of the silicate part of Earth
- CIG: initiative to produce Earth-science software
- crustal magnetism: magnetic fields independent of a world's core magnetic field
- crustal plates: sections of the Earth's crust that move
- equilibrium condensation model: chemical model explaining solar system planet abundances
- geochemistry: the chemistry of the Earth, planets, and moons
- geosignature: geological sign of consequences of life
- graben: depressed block of planet crust
- magma ocean: presumed to occur early in Earth history and potentially on exoplanets
- paleomagnetism: ancient magnetic fields and their characteristics
- permeability: ability of a material to allow fluids to pass through it
- pingo: hill formed of ice
- planetary differentiation: stratification of the materials making up a planet
- polygonal ground: crack pattern in ground forming polygons due to freezing
- regolith: loose solid material covering a planet's solid rock
- seismic waves: waves broadcast through Earth from earthquakes
- siderophile: material that dissolves in molten iron
- silicate: type of compound including silicon and oxygen
- stratigraphy: study of rock layering
- tide: effect of Moon's gravity on Earth's seas, etc.
- weathering: changes in surface due to contact with atmosphere
- geomagnetic storm: disturbance in Earth's magnetosphere
- geometric albedo: see albedo
- geometric delay: see correlator
- geometrical theory of diffraction
- diffraction: an effect of the edge of an obstacle on a wave
- geometry
- geophysics
- geopotential model: see J2
- geopotential model: see gravitational potential model
- GEOS (Groupe Europáen Observations Stellaires): European organization of variable star observers.
- geoseismology
- geosignature: geological sign of consequences of life
- geostationary
- orbital speed: speed of an orbiting body around the barycenter of a system
- geostationary orbit: see synchronous orbit
- geostrophic balance: see thermal wind
- geostrophic wind: see thermal wind
- geosynchronous orbit: see synchronous orbit
- GERLUMPH: hardware/software simulator of lensing light curves
- German
- German Aerospace Center (DLR): German's space and aerotautics research agency
- SOFIA: aircraft-based infrared observatory
- germanium
- r-process: synthesis of elements through neutron capture faster than beta decay
- germanium immersion grating: see immersion grating
- Germanium Observatory for Dark Matter: see Cryogenic Dark Matter Search
- Germany
- Geroch engine (Geroch-Bekenstein engine): hypothetical engine to overcome thermodynamics laws using a black hole
- Geroch process: see Geroch-Bekenstein engine
- Geroch-Bekenstein engine: hypothetical engine to overcome thermodynamics laws using a black hole
- GES: see Gaia
- GEV: see rare designator prefixes
- GF: see rare designator prefixes
- GG Tau: much-studied quadruple star system
- GG Tauri (GG Tau): much-studied quadruple star system
- GGD: see rare designator prefixes
- GGG (Giant Gemini GMOS survey): spectrographic survey of distant quasars
- GGG survey (Giant Gemini GMOS survey): spectrographic survey of distant quasars
- GGM (Goddard gravity model): gravity model produced by Goddard Space Flight Center
- GGM: see MMX
- GH: see Lowell Proper Motion Survey
- GHCG: see rare designator prefixes
- GHO: see rare designator prefixes
- GHOST: see Gemini Observatory
- ghost image: see stray light
- GHRIL: see William Herschel Telescope
- GHRS: see HRS
- GHRS: see Hubble Space Telescope
- GHz peaked spectrum: see radio source
- GI (gravitational instability): instability due to gravity
- GI dynamo: see dynamo
- GI2T: optical interferometer in France
- GIA (Gruppo Italiano Astrometristi): Italian amateur astronomy organization
- GIADA: see Rosetta
- GIANO: see Telescopio Nazionale Galileo
- GIANO-B: see Telescopio Nazionale Galileo
- giant branch
- giant elliptical galaxy: very large elliptical galaxy generally at a galaxy cluster's center
- Giant Gemini GMOS survey: spectrographic survey of distant quasars
- Giant GRB Ring: ring of GRB locations
- giant impact: see impact
- giant impacts: see planet formation
- Giant Magellan Telescope: 24.5 meter telescope under construction
- giant magnetar flare: see magnetar
- Giant Metrewave Radio Telescope: large radio interferometer in India
- giant molecular cloud: interstellar gas cloud with molecules, thousands of solar masses
- giant planet: planet of more than 10 Earth masses
- giant planet formation: process by which giant planets form
- giant planets
- giant pulse: see rotating radio transient
- giant radio galaxy: see radio galaxy
- giant radio source: see radio source
- Giant Segmented Mirror Telescope: concept for an extremely large telescope
- giant star: star larger than main sequence stars
- giant stars
- Giant Stellar Stream: extensive stellar stream in M31
- giant-impact hypothesis: see Moon formation
- giant-impact hypothesis: see impact
- moon: a planet's natural satellite, such as Earth's
- GIARPS: see Telescopio Nazionale Galileo
- GIC: see double star designation
- Giclas (Lowell Proper Motion Survey): 1950s-1970s catalogs of stars with proper motion
- Giclas 29-38: white dwarf variable star of interest
- GIG: see immersion grating
- giga-anum: see gigayear
- GigaBIT: see SuperBIT
- gigaparsec: see parsec
- gigayear: a billion years
- GIMI: see ARGOS
- GIMIC
- EAGLE: simulation of galaxy formation and evolution
- GIMP: see WIMP
- Ginga: 1980s Japanese space X-ray telescope
- Gini
- Gini/M20: an automatable method of detecting whether a galaxy has recently merged
- Gini-M20 (Gini/M20): an automatable method of detecting whether a galaxy has recently merged
- Gini/M20: an automatable method of detecting whether a galaxy has recently merged
- Ginny: see Mars 2020
- GIO (grazing incidence optics): optics that avoid large changes to the angle of rays
- Giotto: 1980s space mission carrying out a Comet Halley flyby
- Giotto Extended Mission: see Giotto
- GIRAFFE: see European Southern Observatory Very Large Telescope
- GIS: see ASCA
- GISMO: 2 mm bolometer camera on IRAM 30 m telescope
- GISMO: see IRAM 30m Telescope
- GISS GCM ModelE: see ROCKE-3D
- GitHub: online software development repositories
- GIZMO
- GJ (Gliese-Jahreiss Catalog): 1991 catalog of stars within 25 parsecs
- GJ 1132: see GJ 1132 b
- GJ 1132 b: Earth-like extrasolar planet discovered in 2015
- GJ 1214: see GJ 1214 b
- GJ 1214 b: super-Earth extrasolar planet discovered in 2009
- GJ 3053 (LHS 1140): red dwarf with rocky planet in its habitable zone
- GJ 406 (Wolf 359): nearby red dwarf
- GJ 436: see Gliese 436 b
- GJ 436 b (Gliese 436 b): hot Neptune found in 2004
- GJ 699 (Barnard's Star): nearby red dwarf
- GJ 699b: see Barnard's Star
- GJ 887 (Lacaille 9352): red dwarf that is the twelfth nearest star system
- GK dwarf
- GKM star: see FGK star
- GL: see AFGL Four Color Infrared Sky Survey
- Gl (Gliese Catalogue of Nearby Stars): 1950s catalog of stars within 20 parsecs
- GLADE: list of galaxies likely to host GW events
- GLADE+: see GLADE
- GLARE: project to search for distant star-forming galaxies
- GLAS: see William Herschel Telescope
- GLASS: see James Webb Space Telescope
- Glass: see rare designator prefixes
- GLAST (Fermi): satellite for studying gamma rays
- Glazar: 1980s UV space telescope on MIR space station
- Glazar: see Kvant 1
- Glazar-1 (Glazar): 1980s UV space telescope on MIR space station
- Glazar-2: see Glazar
- GLE: see double star designation
- GLEAM: MWA radio survey of the southern sky
- GLEAM-X: see GLEAM
- Gliese (Gliese Catalogue of Nearby Stars): 1950s catalog of stars within 20 parsecs
- Gliese 1132: see GJ 1132 b
- Gliese 1132 b (GJ 1132 b): Earth-like extrasolar planet discovered in 2015
- Gliese 1214: see GJ 1214 b
- Gliese 1214 b (GJ 1214 b): super-Earth extrasolar planet discovered in 2009
- Gliese 191 (Kapteyn's Star): nearby M dwarf
- Gliese 388 (AD Leonis): active red dwarf
- Gliese 411 (Lalande 21185): nearby red dwarf
- Gliese 436: see Gliese 436 b
- Gliese 436 b: hot Neptune found in 2004
- Gliese 581
- M-type star: spectral class of star with a temperature in the vicinity of 2500 K
- Gliese 65 (Luyten 726-8): nearby binary star system
- Gliese Catalogue of Nearby Stars: 1950s catalog of stars within 20 parsecs
- Gliese-Jahreiss Catalog: 1991 catalog of stars within 25 parsecs
- GLIMPSE: see Spitzer Space Telescope
- glitch: see pulsar
- GLKA: see rare designator prefixes
- GLMP: see IRAS
- global astrometry: see astrometry
- global climate model: see general circulation model
- Global Exoplanet M-dwarf Search-Survey: a search for exoplanets around m-dwarf stars
- global magnetosphere: see magnetosphere
- Global Microlensing Alert Network (GMAN): collaboration to alert on microlensing transients
- global navigation satellite system: type of space-based service that can impede radio astronomy
- Global Network on Sustainability in Space (GNOSIS): initiative to explore the problem of space debris
- Global Oscillations Network Group: cooperative organization studying the Sun through helioseismology
- Global-scale Observations of the Limb and Disk: satellite instrument to study ionosphere regarding space weather
- globular cluster: spherical group of stars orbiting a galaxy
- globular cluster bimodality: see globular cluster
- globular cluster candidate: see globular cluster
- globular cluster luminosity function: distribution of brightness of globular clusters
- globular cluster specific frequency: see globular cluster
- globular cluster system: see globular cluster
- globular clusters
- GLOWS: see IMAP
- GLP: see double star designation
- GLT (Greenland Telescope): 12 m radio telescope in Greenland
- Glue: visualization software good for astrophysical data
- gluino: see supersymmetry
- gluon: see particle
- gluon: see quark
- Gly (glycine): smallest of the twenty common amino acids
- Gly: see light-year
- glycine: smallest of the twenty common amino acids
- GM: see magnetosphere
- GM: see rare designator prefixes
- GM Aur
- MAPS: ALMA survey researching planet-formation
- GMACS: see Giant Magellan Telescope
- GMAN: collaboration to alert on microlensing transients
- Gmb: see Catalog of Circumpolar Stars
- GMC (giant molecular cloud): interstellar gas cloud with molecules, thousands of solar masses
- GMF: see magnetic field
- GMM: see Galileo
- GMM: see Goddard gravity model
- GMOS: see Gemini Observatory
- GMOS-N: see Gemini Observatory
- GMOS-S: see Gemini Observatory
- GMP: see rare designator prefixes
- GMRT (Giant Metrewave Radio Telescope): large radio interferometer in India
- GMT (Giant Magellan Telescope): 24.5 meter telescope under construction
- GMT - CfA Large Earth Finder (G-CLEF): spectrograph on the GMT
- GMT-consortium Large Earth Finder (G-CLEF): spectrograph on the GMT
- GMTIFS: see Giant Magellan Telescope
- GMTNIRS: see Giant Magellan Telescope
- GN (Atlas of Galactic Nebulae): 1980s catalog of Milky-Way nebulae
- GN: see GOODS-North
- GN-z11: distant galaxy with SMBH of interest
- GNFW profile: see Navarro-Frenk-White profile
- GNIRS: see Gemini Observatory
- GNOSIS: initiative to explore the problem of space debris
- GNS (GOODS NICMOS Survey): survey with HST NICMOS instrument of galaxies in GOODS fields
- GNS-JD2 (GN-z11): distant galaxy with SMBH of interest
- GNSS (global navigation satellite system): type of space-based service that can impede radio astronomy
- GNT: see double star designation
- GO (guest observer): non-affiliated researcher welcomed to use an observatory
- GO program: see guest observer
- GOALS: across-spectrum observation of 200 LIRGs
- GOALS-JWST: see GOALS
- GOBELINS (Gould's Belt Distances Survey): survey of parallax distances to Gould's Belt YSOs
- Goddard (Goddard Space Flight Center): NASA space research laboratory near Washington D.C.
- Goddard Earth Gravity Model: see Goddard gravity model
- Goddard gravitational model (Goddard gravity model): gravity model produced by Goddard Space Flight Center
- Goddard gravity model: gravity model produced by Goddard Space Flight Center
- Goddard High Resolution Spectrograph: see HRS
- Goddard IRAM Superconducting Two Millimeter Camera (GISMO): 2 mm bolometer camera on IRAM 30 m telescope
- Goddard Lunar Gravity Model: see Goddard gravity model
- Goddard Mars Gravity Model: see Goddard gravity model
- Goddard Mars Model: see Goddard gravity model
- Goddard Space Flight Center: NASA space research laboratory near Washington D.C.
- Godunov method (Godunov scheme): computational fluid dynamics method
- Godunov scheme: computational fluid dynamics method
- Godunov's scheme (Godunov scheme): computational fluid dynamics method
- GOLD (Global-scale Observations of the Limb and Disk): satellite instrument to study ionosphere regarding space weather
- Goldilocks zone (habitable zone): zone where conditions are favorable for life
- Goldstone Deep Space Communications Complex: see NASA Deep Space Network
- GOLF: see Solar and Heliospheric Observatory
- GONG (Global Oscillations Network Group): cooperative organization studying the Sun through helioseismology
- Good Solar Telescope: see Big Bear Solar Observatory
- Goodman HTS: see SOAR Telescope
- GOODS: survey combining data from different sources on very distant objects
- GOODS 850: see rare designator prefixes
- GOODS NICMOS Survey: survey with HST NICMOS instrument of galaxies in GOODS fields
- GOODS-N: see GOODS
- DEEP2: redshift survey of 60,000 galaxies
- Goods-N (GOODS-North): moderate size survey field
- GOODS-North: moderate size survey field
- GOODS-North: see GOODS
- DEEP2: redshift survey of 60,000 galaxies
- GOODS NICMOS Survey: survey with HST NICMOS instrument of galaxies in GOODS fields
- GOODS-S (GOODS-South): moderate size survey field
- GOODS-S: see GOODS
- GOODS-South: moderate size survey field
- GOODS-South: see GOODS
- GoreSat (DISCOVR): space weather satellite
- GOS (Galactic O Star Catalog): 2000s catalog of O-type stars
- GOSC (Galactic O Star Catalog): 2000s catalog of O-type stars
- GOSSS: see Galactic O Star Catalog
- Gould Belt (Gould's Belt): ring of stars around the sky
- Gould designation: see Flamsteed designation
- Gould's Belt: ring of stars around the sky
- Gould's Belt Distances Survey: survey of parallax distances to Gould's Belt YSOs
- GP (pea galaxy): small greenish galaxy
- GP: see rotating radio transient
- GP-B (Gravity Probe B): space experiment re GR effects of Earth gravity
- GPC: see Pan-STARRS
- Gpc: see parsec
- GPD (gas pixel detector): type of X-ray imager sensitive to polarization
- GPI (Gemini Planet Imager): infrared instrument to overcome signal noise imaging exoplanets
- GPI: see Gemini Observatory
- GPI 2.0: see Gemini Planet Imager
- GPIPS
- Mimir: multi-function near-infrared instrument on Perkins Telescope
- GPR: see radar
- GPS: see EXOSAT
- GPS: see UKIDSS
- GPS: see radio source
- time dilation: relativity's ability to make time differ for different objects
- GPU: type of CPU tailored to handling computer graphics
- GERLUMPH: hardware/software simulator of lensing light curves
- GPU Supercomputer for Theoretical Astrophysics Research: supercomputer at Swinburne University
- GPU-D: see GERLUMPH
- GPU-Enabled, High-Resolution, cosmological Microlensing parameter survey (GERLUMPH): hardware/software simulator of lensing light curves
- GPX: amateur effort to uncover exoplanets within the galactic plane
- GR (gamma rays): electromagnetic radiation, wavelength 10 picometers and less
- GR (general relativity): formula relating gravity, space, time, and mass
- GR: see rare designator prefixes
- Big Bang: theoretical event when the universe expanded from a point
- bigravity: modifications to GR defining two metrics
- effective field theory: type of useful simplification of a field theory
- f(R) gravity: class of modifications to general relativity
- Lambda-CDM model: Big-Bang cosmological model with a cosmological constant and cold dark matter
- LARES: satellite to test a general relativity effect
- metric: mathematical generalization of the concept of distance
- scalar-tensor gravity: GR-like gravity that incorporates a scalar field
- Shapiro delay: EMR delay due to passing near massive object
- wCDM: Big-Bang cosmological model with constant cosmological equation of state
- worldline: path of an object through space and time
- GR*: see Lowell Proper Motion Survey
- GR1D: core collapse supernova simulation in 1D with GR
- graben: depressed block of planet crust
- GRACE: see William Herschel Telescope
- GRACES: see Gemini Observatory
- gradient: vector indicating the slope at a point within a field
- gradient: see mathematical field
- gradient boosting
- gradient field: see gradient
- GRADPAK: see WIYN 3.5m Telescope
- GRAIL: 2011 NASA lunar orbiters to collect gravity data
- GRAIL A: see GRAIL
- GRAIL B: see GRAIL
- grain: see cosmic dust
- grams per mole
- Gran Tecan (Gran Telescopio Canarias): 10.4 meter telescope in the Canary Islands
- Gran Telescopio Canarias: 10.4 meter telescope in the Canary Islands
- Gran Telescopio Milimétrico (Large Millimeter Telescope): large microwave telescope in Mexico
- GRANAT: observatory-satellite for detecting gamma rays and X-rays
- GRaND: see Dawn
- grand design spiral galaxy: spiral galaxy with two just two arms that are well-defined
- Grand Interféromètre a 2 Télescopes (GI2T): optical interferometer in France
- grand tack hypothesis: solar system formation model with Jupiter and Saturn migrating
- Grand Unified Theory: see Theory of Everything
- Grand Unified Theory: see strong force
- electroweak: single conception including both electromagnetic and weak forces
- symmetry breaking: loss of symmetry, such as due to loss of stability in a regime change
- grandmoon (subsatellite): object orbiting a moon
- granulation: see Sun
- granule: see Sun
- granule: see Sun surface features
- facula: bright spot on a planet or the Sun
- GRAPES-3: Cherenkov telescope at Ooty, India
- graph
- error bar: feature of a graph to indicate accuracy
- Gabbard plot: plot showing apogee-perigee range of select orbiting debris
- graph theory
- dendrogram: diagram of a "tree", i.e., of a graph without cycles
- graphic information processor
- GERLUMPH: hardware/software simulator of lensing light curves
- graphics processing unit (GPU): type of CPU tailored to handling computer graphics
- grating: spectrometer component
- disperser: prism, grating, or grism within a spectrometer
- grism: combination of a grating and a prism
- grating prism (grism): combination of a grating and a prism
- grating spectrometer: see grating
- GRAV: see Juno
- gravimeter: see gravimetry
- admittance: effect of atmospheric pressure on gravity
- gravimetry: measurement of gravity's strength
- admittance: effect of atmospheric pressure on gravity
- Bouguer anomaly: gravity's local variation after compensating for altitude and landforms
- free-air anomaly: gravity's local variation after compensating for altitude
- gravity anomaly: difference between measured gravity and that predicted by a model
- gravistar: theoretical type of black hole with certain contents
- gravitation (gravity): theory that mass attracts
- gravitational binding energy: see binding energy
- gravitational collapse: shrinking of an object from gravitational force
- gravitational collapse energy: see gravitational collapse
- gravitational constant: indicates how much pull between two masses
- gravitational energy (gravitational potential energy): energy implied by some mass being some distance from another
- Gravitational European Observatory (GEO600): ground-based gravitational-wave detector in Germany
- gravitational field: gravitational force as distributed over a space
- gravitational force: see gravity
- gravitational harmonics: see J2
- gravitational instability: instability due to gravity
- gravitational instability dynamo: see dynamo
- gravitational instability model: model for the formation of giant planets
- gravitational instability model: see giant planet formation
- gravitational lens: see gravitational lensing
- gravitational lensing: focusing electromagnetic radiation by gravitational force
- gravitational locking (tidal locking): locked rotation of an orbiting body
- gravitational mass: see mass
- gravitational microlensing: gravitational lensing by "small" objects such as individual stars and planets
- gravitational model (gravitational potential model): mathematical model of an astronomical body's gravitational field
- gravitational moment: see J2
- gravitational nanolensing: see gravitational microlensing
- gravitational potential: conceptual field indicating the strength of gravity at each point
- gravitational potential energy: energy implied by some mass being some distance from another
- gravitational potential model: mathematical model of an astronomical body's gravitational field
- Goddard gravity model: gravity model produced by Goddard Space Flight Center
- J2: geopotential coefficient regarding a planet's oblateness
- gravitational potential well: a dip in the gravitational-potential field
- gravitational primary (primary): central body of a system such as the Sun within the solar system
- gravitational pumping: see planet formation
- gravitational quadrupole radiation
- gravitational radiation (gravitational wave): ripples in the curvature of spacetime propagating as a wave
- gravitational radius (Schwarzschild radius): radius of a black hole's event horizon
- gravitational redshift: redshift due to GR effects of gravity
- gravitational scattering: see planetary migration
- gravitational separation
- gravitational singularity: point where density and gravity reach infinity
- gravitational slingshot (gravity assist): method of boosting the speed of a spacecraft
- gravitational sounding (gravity sounding): measuring a planet's gravitation field by study of nearby probe flights
- gravitational spectrum: see J2
- gravitational time delay
- gravitational time dilation: see time dilation
- gravitational wave: ripples in the curvature of spacetime propagating as a wave
- gravitational wave astronomy: see gravitational wave
- gravitational wave background: combination of weak gravitational waves such as from distant sources
- gravitational wave background: see gravitational wave
- gravitational wave detection (GW detection): observed gravitational wave signal recognizable as an astronomical event
- gravitational wave detection: see gravitational wave
- gravitational wave event: see GW detection
- gravitational wave event: see gravitational wave
- Gravitational Wave Galaxy Catalogue: list of probable galaxies for GW detections
- gravitational wave spectrum: various frequencies of gravitational waves
- gravitational wave strain: a measure of the magnitude of a gravitational wave
- Gravitational Wave Transient Catalog: catalog of gravitational wave detections
- gravitational waves
- gravitational well (gravitational potential well): a dip in the gravitational-potential field
- gravitational-wave detector: device to detect gravitational waves
- gravitational-wave memory: a gravitational wave that does not return
- gravitational-wave observatory (gravitational-wave detector): device to detect gravitational waves
- gravitationally bound: description of objects kept together by gravity
- gravitationally interacting massive particle: see WIMP
- gravithermal catastrophe
- gravitino: see supergravity
- gravito-magnetism: see gravitomagnetic field
- gravitoelectromagnetism: see gravitomagnetic field
- gravitomagnetic field: magnetic-like-field produced by gravitation
- gravitomagnetism: see gravitomagnetic field
- gravitometer: see gravimetry
- graviton: quantum of gravity
- supergravity: combination of general relativity and supersymmetry
- gravitoturbulence: see gravitational instability model
- GRAVITY: see European Southern Observatory Very Large Telescope
- gravity: theory that mass attracts
- gravity anomaly: difference between measured gravity and that predicted by a model
- gravity assist: method of boosting the speed of a spacecraft
- Venus: second inner-most planet in the solar system
- Gravity B (Gravity Probe B): space experiment re GR effects of Earth gravity
- gravity crystal: see Wigner crystal
- gravity harmonics: see J2
- gravity model (gravitational potential model): mathematical model of an astronomical body's gravitational field
- Gravity Probe B: space experiment re GR effects of Earth gravity
- Gravity Recovery and Interior Laboratory (GRAIL): 2011 NASA lunar orbiters to collect gravity data
- gravity sounding: measuring a planet's gravitation field by study of nearby probe flights
- gravity spectrum: see J2
- gravity traverse: see gravimetry
- gravity wave: wave in fluid where restoring force is gravity
- gravity well (gravitational potential well): a dip in the gravitational-potential field
- GRAVITY+: see European Southern Observatory Very Large Telescope
- gravity-sensitive spectral lines: see surface gravity
- gray atmosphere: a model atmosphere whose opacity does not depend upon wavelength
- gray body: ideal object that reflects the same fraction of light at any wavelength
- graybody (gray body): ideal object that reflects the same fraction of light at any wavelength
- grazing angle: see grazing incidence optics
- grazing incidence optics: optics that avoid large changes to the angle of rays
- grazing incident optics
- NICER: space X-ray mission specifically to view neutron stars
- NuSTAR: space telescope for high-energy X-rays
- Wolter telescope: reflector telescope using only shallow-angle reflections
- grazing planet: see transiting planet
- GRB (gamma-ray burst): short flash of gamma rays apparently from outside our galaxy
- GRB: see Ulysses
- GRB 060505: GRB without an expected SN
- GRB 170817A: see GW170817
- GRB 190114C: well-studied GRB
- GRB 980425: see SN 1998bw
- GRB afterglow: see gamma-ray burst
- GRB lightcurve: see gamma-ray burst
- GRB optical transient: see gamma-ray burst
- GRB progenitor: see gamma-ray burst
- GRB-SN (GRB-supernova): supernova that produces a GRB
- GRB-supernova: supernova that produces a GRB
- GRBs
- BAT6: sample of long GRBs
- GRB-supernova: supernova that produces a GRB
- Konus-Wind catalog: catalog of GRBs from the Wind spacecraft
- localization: ability to identify location of a transient
- mass extinction: event in which many species went extinct
- TAROT: network of telescopes to catch GRB optical counterparts
- THESEUS: plan for X-ray/Gamma-ray transient space mission
- VERITAS: ground gamma ray telescope array in Arizona
- GRE: see Giotto
- GREAT: see SOFIA
- Great Andromeda Nebula: see Andromeda
- Great Attractor: gravity anomaly at the center of our supercluster
- Great Blue Spot: see magnetic field
- Great Carina Nebula (Carina Nebula): HII region with stars and nebulae of interest
- great circle: see meridian
- Great Dark Spot: see Neptune
- Great Debate: historical debate regarding the nature of galaxies
- Great Dimming: see Betelgeuse
- Great Eruption: see Eta Carinae
- Great Observatories All-Sky LIRG Survey (GOALS): across-spectrum observation of 200 LIRGs
- Great Observatories Origins Deep Survey (GOODS): survey combining data from different sources on very distant objects
- great oxidation event: see reducing atmosphere
- Great Red Spot: see Jupiter
- Great Rift: see Cygnus-X
- Great Void
- void: empty spaces between large scale structures
- Great Wall: large slab of galaxies
- green
- G band: band of visible light around 5100 angstroms
- Green Bank 140 Foot Telescope: West Virginia radio telescope
- Green Bank 1st survey: see Green Bank 6-cm Radio Source Catalog
- Green Bank 2nd survey: see Green Bank 6-cm Radio Source Catalog
- Green Bank 300ft Telescope: former large radio telescope at Green Bank
- Green Bank 300ft Transit Radio Telescope (Green Bank 300ft Telescope): former large radio telescope at Green Bank
- Green Bank 3rd survey: see Green Bank 6-cm Radio Source Catalog
- Green Bank 6-cm Radio Source Catalog: catalog of from 1980s northern-hemisphere radio survey
- Green Bank 90m Telescope (Green Bank 300ft Telescope): former large radio telescope at Green Bank
- Green Bank 91m Telescope (Green Bank 300ft Telescope): former large radio telescope at Green Bank
- Green Bank C survey: see Green Bank 6-cm Radio Source Catalog
- Green Bank Observatory: radio observatory in West Virginia including GBT
- Green Bank Telescope: West Virginia large radio telescope
- Breakthrough Listen: SETI survey using GBT and Parkes Observatory
- GUPPI: radio-telescope back-end aimed at processing pulsar data
- Green Bank Ultimate Pulsar Processing Instrument (GUPPI): radio-telescope back-end aimed at processing pulsar data
- green galaxy: see galaxy main sequence
- green pea (pea galaxy): small greenish galaxy
- green pea galaxy (pea galaxy): small greenish galaxy
- green valley: see galaxy main sequence
- green valley galaxy: see galaxy main sequence
- greenhouse effect: mechanism that boosts temperature through selective blocking of EMR
- greenhouse gas: see greenhouse effect
- earthshine: reflected and emitted electromagnetic radiation from Earth
- Greenland
- Greenland Telescope: 12 m radio telescope in Greenland
- Greenwich mean time
- time standard: method of designating points in time and quantifying time periods
- Greenwich meridian: see meridian
- time standard: method of designating points in time and quantifying time periods
- Greenwood time constant: see seeing
- Gregorian calendar: see Julian calendar
- Gregorian telescope: type of reflector telescope
- Gregorian year: see Julian calendar
- Greisen-Zatsepin-Kuzmin effect (GZK limit): limit on energy of cosmic rays
- Greisen-Zatsepin-Kuzmin limit (GZK limit): limit on energy of cosmic rays
- grey atmosphere (gray atmosphere): a model atmosphere whose opacity does not depend upon wavelength
- grey body (gray body): ideal object that reflects the same fraction of light at any wavelength
- GRG: see radio galaxy
- GrG (galaxy group): group of fifty or fewer gravitationally-bound Milky-Way-sized galaxies
- GRID: see AGILE
- Griffith Observatory: see Galileo Observatory
- Grigg-Skjellerup
- Giotto: 1980s space mission carrying out a Comet Halley flyby
- grism: combination of a grating and a prism
- disperser: prism, grating, or grism within a spectrometer
- grating: spectrometer component
- Grism Lens-Amplified Survey from Space: see James Webb Space Telescope
- grism spectrograph: see grism
- grism spectroscopy: see grism
- griz photometric system: photometric system designed for electronic sensors
- GRMHD: see magnetohydrodynamics
- GRNS: see Psyche
- GRO (Compton Gamma Ray Observatory): 1990s space observatory for gamma ray observation
- GRO J1655-40: microquasar
- GROCSE: see ROTSE
- Groombridge (Catalog of Circumpolar Stars): list of over 4000 stars in northern part of the sky
- gross structure: see fine structure
- gross structure: see hyperfine structure
- Groth Strip: region of sky in early HST survey
- Groth Strip Survey: see Groth Strip
- Groth-Westphal Strip (Groth Strip): region of sky in early HST survey
- ground
- ground state: lowest energy level
- ground state: see state of excitation
- Ground-Base Electro-Optical Deep Space Surveillance: initiative to track artificial spacecraft including space junk
- ground-penetrating radar: see radar
- Group: see rare designator prefixes
- group
- group environment: see galaxy environment
- Group Evolution Multiwavelength Study: survey of galaxy groups
- group of galaxies (galaxy group): group of fifty or fewer gravitationally-bound Milky-Way-sized galaxies
- Groupe Europáen Observations Stellaires: European organization of variable star observers.
- growth barrier (barrier): challenging issue regarding planet formation
- GRS: see GRANAT
- GRS: see Jupiter
- GRS: see Lunar Prospector
- GRS: see MESSENGER
- GRS: see Mars Observer
- GRS: see Mars Odyssey
- GRS: see SELENE
- GRS: see Solar Maximum Mission
- GRS: see radio source
- GRS 1915+105: stellar-mass black hole microquasar
- Gruppo Italiano Astrometristi: Italian amateur astronomy organization
- Grus Wall: see galaxy filament
- GRV: see rare designator prefixes
- GRW: see Astrographic Catalog
- GS (guide star): star used to assist in astronomical observation
- GS: see GOODS-South
- GS: see Ginga
- GS: see Juno
- GS: see rare designator prefixes
- Gs (gauss): measurement of magnetic field β
- GSAOI: see Gemini Observatory
- GSC (Guide Star Catalog): catalog of stars to help aim HST
- GSC-I: see Guide Star Catalog
- GSC-II: see Guide Star Catalog
- GSC2: see Guide Star Catalog
- GSFC (Goddard Space Flight Center): NASA space research laboratory near Washington D.C.
- GSFC xray and EUV Spectroheliograph: see OSO 7
- GSH: see double star designation
- GSh: see rare designator prefixes
- GSMT (Giant Segmented Mirror Telescope): concept for an extremely large telescope
- GSPC: see Guide Star Catalog
- GSPC-I: see Guide Star Catalog
- GSPC-II: see Guide Star Catalog
- GSS (Giant Stellar Stream): extensive stellar stream in M31
- GSS: see Groth Strip
- GSS: see rare designator prefixes
- GST: see Big Bear Solar Observatory
- gSTAR (GPU Supercomputer for Theoretical Astrophysics Research): supercomputer at Swinburne University
- GT: see rare designator prefixes
- GTC (Gran Telescopio Canarias): 10.4 meter telescope in the Canary Islands
- GTC-HRS: see Gran Telescopio Canarias
- GTCAO+FRIDA: see Gran Telescopio Canarias
- GTM (Large Millimeter Telescope): large microwave telescope in Mexico
- GTO: see James Webb Space Telescope
- Guangzhou Zhongke Aerospace Exploration Technology Co. (CAS Space): Chinese commericial space-launch corporation
- Guaranteed Time Observations: see James Webb Space Telescope
- guest observer: non-affiliated researcher welcomed to use an observatory
- guest observer program: see guest observer
- guest star: translation of ancient Chinese term for a visible transient
- guide star: star used to assist in astronomical observation
- Guide Star Astrometric Support Package: software to assist in using guide stars for HST observations
- Guide Star Catalog: catalog of stars to help aim HST
- Guide Star Photometric Catalog: see Guide Star Catalog
- guidestar (guide star): star used to assist in astronomical observation
- guillotine factor
- Gulf of Mexico
- Chicxulub crater: ancient giant impact crater under Mexico and the Gulf of Mexico
- Gum: see rare designator prefixes
- Gunn photometric system (griz photometric system): photometric system designed for electronic sensors
- Gunn-i: see griz photometric system
- DENIS: 1990s southern sky survey of two near-infrared bands
- Gunn-Peterson effect: see Gunn-Peterson trough
- Gunn-Peterson optical depth: see Gunn-Peterson trough
- Gunn-Peterson trough: spectral feature in EMR from redshift 6+
- Guo Shoujing Telescope (LAMOST): Chinese telescope for spectroscopic surveys of stars and galaxies
- GUPPI: radio-telescope back-end aimed at processing pulsar data
- GUPPI: see Green Bank Telescope
- GUSTO: balloon-borne 0.9-m far-infrared telescope
- GUT: see Theory of Everything
- GUT: see strong force
- electroweak: single conception including both electromagnetic and weak forces
- symmetry breaking: loss of symmetry, such as due to loss of stability in a regime change
- GUVI: see TIMED
- GUVV: see Galaxy Evolution Explorer
- GV: see rare designator prefixes
- GW (GW detection): observed gravitational wave signal recognizable as an astronomical event
- GW (galactic worm): high density streak of HI perpendicular to galactic plane
- GW (gravitational wave): ripples in the curvature of spacetime propagating as a wave
- GW background (gravitational wave background): combination of weak gravitational waves such as from distant sources
- GW detection: observed gravitational wave signal recognizable as an astronomical event
- GW detector (gravitational-wave detector): device to detect gravitational waves
- GW event: see GW detection
- GW memory (gravitational-wave memory): a gravitational wave that does not return
- GW observatory (gravitational-wave detector): device to detect gravitational waves
- GW spectrum (gravitational wave spectrum): various frequencies of gravitational waves
- GW strain (gravitational wave strain): a measure of the magnitude of a gravitational wave
- GW150914: see GW detection
- GW150914: see gravitational wave
- LIGO: pair of observatories to detect gravitational waves
- GW151226: see GW detection
- GW170104: see GW detection
- GW170608: see GW detection
- GW170814: see GW detection
- GW170817: 2017 gravitational wave detection from a neutron star merger
- GW170817: see GW detection
- standard siren: transient whose gravitational waves indicate a specific distance
- GWB (gravitational wave background): combination of weak gravitational waves such as from distant sources
- GWB: see gravitational wave
- GWE: see Ulysses
- GWGC (Gravitational Wave Galaxy Catalogue): list of probable galaxies for GW detections
- GWs
- GWTC (Gravitational Wave Transient Catalog): catalog of gravitational wave detections
- GWTC-1: see Gravitational Wave Transient Catalog
- GWTC-2: see Gravitational Wave Transient Catalog
- GWTC-2.1: see Gravitational Wave Transient Catalog
- GWTC-3: see Gravitational Wave Transient Catalog
- GX: see X-ray source
- GY: see rare designator prefixes
- Gy (gigayear): a billion years
- Gya: see gigayear
- GYL: see double star designation
- Gyr (gigayear): a billion years
- GYRE: a stellar oscillation code
- gyrochronology: means of estimating stellar age from rotation
- GZ2 (Galaxy Zoo 2): crowd-sourced classification of hundreds of thousands of galaxies
- GZK effect (GZK limit): limit on energy of cosmic rays
- GZK horizon: see GZK limit
- GZK limit: limit on energy of cosmic rays
- GZK neutrino: see GZK limit
Index