| Furukawa observatory | Japón | Hida | — |
| Fushan observatory | República Popular China | Huazhou (Weinan) | — |
| 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 | — |