| Abbreviation | Definition |
|---|---|
| GAM | Global Astronomy Month |
| GASA | Graduate Astronomy Students Association |
| GB | Guide Brightness |
| GBT | Green Bank Telescope |
| GCC | Globular Cluster Candidate |
| GDSO | Georgi Dobrovolski Solar Observatory |
| GGC | Giant Gravity Core |
| GHA | Greenwich Hour Angle |
| GHI | Global Horizontal Irradiance |
| GHZ | Galactic Habitable Zone |
| GML | Galactic Modeling Language |
| GMOS | Gemini Multi-Object Spectrographs |
| GMT | Giant Magellan Telescope |
| GMT | Greenwich Mean Time (now obsolete) |
| GN | Galactic Nebula |
| GNAT | Global Network of Astronomical Telescopes |
| GNN | Galactic Nebulae Navigator |
| GPE | Gravitational Potential Energy |
| GPS | Geo Positioning System |
| GR | Galactic Rotation |