| Abbreviation | Definition |
|---|---|
| HRV | High-Resolution Visible |
| HS | Horizontal System |
| HSD | Heliophysics Science Division |
| HTFA | High Temperature Flowing Afterglow |
| HVR | Hyper-Variable Region |
| HZ | Habitable Zone |
| IAAC | Internet Amateur Astronomers Catalog |
| IAO | International Astronomy Olympiad |
| IAPG | Institute for Astronomical and Physical Geodesy |
| IARA | Italian Amateur Radio Astronomy |
| IAS | Indiana Astronomical Society |
| IASC | International Astronomical Search Collaboration |
| IAU | International Astronomical Union |
| IAU | Irrelevant Astronomical Union |
| IB | Interstellar Band |
| IBBTF | Imagination Baffled By The Facts |
| ICET | International Center for Earth Tides |
| ICRAR | International Centre for Radio Astronomy Research |
| ICRC | International Cosmic Ray Conference |
| ICSO | International Conference on Space Optics |