| G. C. Gloriosi Astronomical Observatory | Italia | Salerno | — |
| G. Colombo Astronomical Observatory | Italia | Padua | — |
| G. Pascoli Observatory | Italia | Castelvecchio Pascoli | — |
 G.V. Schiaparelli Observatory | Italia | Varese | 1.226 m |
| Gaertringen observatory | Alemania | Gärtringen | — |
 Gahberg Observatory | Austria | Weyregg am Attersee | 860 m |
 Gaia | — | — | — |
 Gaithersburg Latitude Observatory | Estados Unidos | Maryland | — |
| Galati observatory | Rumania | Epístola a los Gálatas | — |
| Galaxy Blues Observatory | Canadá | Gatineau | — |
| Galaxy Tibet YBJ Observatory | República Popular China | Damxung | — |
 Galbergweg 12 | Alemania | Gotha | — |
 GALEX | — | — | — |
| Galhassin Robotic Telescope observatory | Italia | Isnello | — |
| Galileo Galilei Observatory | Argentina | Oro Verde | — |
 Galileum Solingen | Alemania | Solingen | — |
| Galleywood observatory | Reino Unido | Galleywood | — |
 Gallium–germanium neutrino telescope | — | — | — |
 Gamma | — | — | — |
| Gan Magnetic Observatory | Maldivas | — | — |
| Gandia observatory | España | Gandía | — |
 Garden observatory of Siegfried Gebhard | Alemania | Dresde | — |
| Gartensternwarte Schafsweide | Alemania | Elze | — |
 Gauribidanur Radio Observatory | India | — | — |
| Gauteng observatory | Sudáfrica | Randburg | — |
| Gedney House Observatory | Reino Unido | Kirton | — |
| Geel observatory | Bélgica | Geel | — |
| Gehrden observatory | Alemania | Gehrden | — |
 Gelber Turm | Alemania | Hildesheim | 206 m |
| Gelenau observatory | Alemania | Gelenau | — |
| Gemeaux Observatory | Canadá | Laval | — |
 Gemini South | Chile | Elqui | 2.722 m |
| Geminiano Montanari Observatory | Italia | Cavezzo | 18 m |
| Geminis Austral observatory | Argentina | Rosario | — |
| Genoa observatory | Italia | Génova | — |
| GenShtab Observatory | Ucrania | península de Crimea | — |
| Geodetic Observatory Wettzell | Alemania | — | — |
 Geophysical Observatory Collm | Alemania | Wermsdorf | — |
 Geophysical Observatory in Racibórz | Polonia | Racibórz | 211 m |
| Geophysikalisches Observatorium Fürstenfeldbruck | Alemania | — | — |
 Georgetown University Astronomical Observatory | Estados Unidos | Washington D. C. | — |
 Georgia College Observatory | Estados Unidos | Milledgeville | — |
 Georgian National Astrophysical Observatory | Georgia | Abastumani | 1.650 m |
 Geospatial Information Authority of Japan | Japón | Kitasato | — |
| GERmanium Detector Array | Italia | — | — |
| Gettysburg College Observatory | Estados Unidos | Pensilvania | — |
| Gevelsberg observatory | Alemania | Breckerfeld | — |
| Geyserland Observatory | Nueva Zelanda | Rotorua Lakes District | — |
| Ghana Satellite Earth Station | Ghana | Ga Oeste | — |
| Ghezz observatory | Suiza | Acquarossa | — |
| GiaGa Observatory | Italia | Pogliano Milanese | — |
| Gibraltar Point Bird Observatory | Reino Unido | — | — |
| Gieres observatory | Francia | akja | — |
 Gifford Observatory | Nueva Zelanda | Región de Wellington | — |
 Gifu Astronomical Observatory | Japón | Gifu | — |
| Gimhae observatory | Corea del Sur | Gimhae | — |
| Gingin Magnetic Observatory | Australia | Western Australia | — |
| GINOP-KHK observatory | Hungría | Mátraszentimre | — |
| Giordano Bruno National Astronomical Observatory and Planetarium | Bulgaria | Dimitrovgrad | — |
| Giordano Bruno Observatory | Italia | Brallo di Pregola | — |
 Girawali Observatory | India | — | — |
| Gissar Observatory | Tayikistán | Hisor | 743 m |
| Giuseppe Conzo's Observatory | Italia | — | — |
| Giuseppe Piazzi observatory | Italia | Ponte in Valtellina | — |
 Givatayim Observatory | Israel | Distrito de Tel Aviv | — |
| Glasgow observatory | Reino Unido | Ciudad de Glasgow | — |
 Glashütte Observatory | Alemania | Glashütte | — |
 Glen D. Riley Observatory | Estados Unidos | Illinois | — |
| Glenlea Astronomical Observatory | Canadá | Winnipeg | — |
| Glenlea Magnetic Observatory | Canadá | — | — |
| Glenlee Observatory | Australia | Glenlee | — |
| Glentower, Auchintore Road, Fort William | Reino Unido | Highland | — |
| Global Oscillations Network Group | España | — | — |
| Glyn Marsh Observatory | Reino Unido | Isla de Man | — |
| Gnangara Magnetic Observatory | Australia | Western Australia | — |
| Gnevsdorf observatory | Alemania | Buchberg | — |
 GNS Science | Nueva Zelanda | — | — |
| Go-Chome and Kobe-Suma observatory | Japón | Kobe Bryant | — |
| Goat Mountain Astronomical Research Station | Estados Unidos | Homestead | — |
| Godalming observatory | Reino Unido | Godalming | — |
 Godlee Observatory | Reino Unido | Mánchester | — |
 Golden Ears Observatory | Canadá | Maple Ridge | 41 m |
| Golden Hill Observatory | Reino Unido | Sturminster Newton | — |
 Goldendale Observatory State Park | Estados Unidos | Washington | — |
| Goma Volcanological Observatory | República Democrática del Congo | Goma | — |
 Goodsell Observatory | Estados Unidos | Northfield | — |
| Gor City Observatory | — | — | — |
| Gorgonzola Observatory | Italia | Gorgonzola | — |
 Gornergrat Kulm Hotel | Suiza | Zermatt | — |
| Gothers Observatory | Reino Unido | St Austell | — |
| GOTO-N | — | — | — |
| GOTO-S | Australia | New South Wales | — |
| Gottolengo observatory | Italia | Gottolengo | — |
| Governor Aker Observatory | Estados Unidos | Safford | — |
| GOZ observatory | Canadá | Lac Schryer | — |
 Grainger Observatory | Estados Unidos | Exeter | — |
 Granat | — | — | — |
| Granda observatory | Italia | Aviatico | — |
| Grange Observatory | Italia | Bussoleno | — |
| Grant O. Gale Observatory | Estados Unidos | Iowa | — |
| Grantham observatory | Reino Unido | Grantham | — |
| Granville observatory | Estados Unidos | Massachusetts | — |
| Grasslands Observatory | Estados Unidos | Tucson | — |
| Gravelle observatory | Francia | Saint-Maurice | — |
| Gravesend observatory | Reino Unido | Gravesham | — |
| Gravina in Puglia observatory | Italia | Gravina in Puglia | — |
 Gravitational-wave detector | — | — | — |
 Gravitational-wave Optical Transient Observer | — | — | — |
 Gravity and Extreme Magnetism Small Explorer | — | — | — |
 Graz-Lustbühel satellite station | Austria | Styria | — |
| Great Basin Bird Observatory | Estados Unidos | — | — |
| Great Shefford Observatory | Reino Unido | Great Shefford | — |
 Green Bank Observatory | Estados Unidos | Condado de Pocahontas | 818 m |
| Green Island observatory | Chipre | Lefkoniko | — |
 Green Point Observatory | Australia | New South Wales | — |
 Greenhill Observatory | Australia | Tasmania | 646 m |
| Greenmoor Observatory | Reino Unido | Woodcote | — |
| Greens Norton observatory | Reino Unido | Greens Norton | — |
| Greenwich Park magnetic observatory | Reino Unido | Municipio de Greenwich | — |
| Greiner Research Observatory | Estados Unidos | Cross Plains | — |
| Grems Timmons Observatories | Estados Unidos | Graettinger | — |
| Gretz-Armainvilliers Observatory | Francia | Gretz-Armainvilliers | — |
| Griffin Hunter Observatory | Estados Unidos | Bethune-Cookman University | — |
| Grocka Magnetic Observatory | Serbia | — | — |
| Gromme observatory | Bélgica | Maasmechelen | — |
| Groruddalen Optical Observatory | Noruega | Oslo | — |
| Grosshabersdorf observatory | Alemania | Großhabersdorf | — |
| Ground measuring point 1 | Kazajistán | Karmakshy District | — |
| Grove Creek Observatory | Australia | New South Wales | — |
| GROWTH India Telescope, IAO | India | Eugen Hänle | — |
| Gruppo Astrofili Catanesi | Italia | Catania | — |
| GSHS Observatory | Corea del Sur | Suwon | — |
| Guadarrama Observatory | España | Madrid | — |
| Gualba Observatory | España | Gualba | — |
| Guam Magnetic Observatory | Estados Unidos | — | — |
| Guernanderf observatory | Francia | Grand-Champ | — |
| Guidestar Observatory | Alemania | Weinheim | — |
| Guido Ruggieri Observatory | Italia | Padua | — |
| Guimar observatory | Canarias | Santa Úrsula | — |
| Guimar-Tenerife Magnetic Observatory | España | — | — |
| Guirguillano Observatory | España | Guirguillano | — |
| Guitalens observatoire | Francia | Guitalens | — |
| Gumma Astronomical observatory | Japón | Takayama Onsen Fureai Plaza | — |
 Gunma Astronomical Observatory | Japón | Takayama (Gunma) | — |
 Gurley Observatory | Estados Unidos | Marietta | — |
 GUSTO | — | — | — |
| Gwen Observatory | Italia | San Francesco al Campo | — |
| Gyodongdo Manhyangdae | Corea del Sur | — | — |
 Göttingen Observatory | Alemania | Gotinga | — |