| 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 | — |