| Abbreviation | Definition |
|---|---|
| AMSU | Advanced Mass Spectrometry Unit |
| ANI | Anterior Nebulae Integration |
| ANS | Astronomical Netherlands Satellite |
| AO | Astronomical Observatory |
| AOA | ASCA Online Arxiv |
| AOAS | Arkansas/Oklahoma Astronomical Society |
| AOB | Astronomical Observatory Belgrade |
| AOB | Astronomical Observatory of Belgrade |
| AOSS | AURA Observatory Support Services |
| AP | Astral Projection |
| APASS | AAVSO Photometric All-Sky Survey |
| APDA | Astronomical Photographic Data Archive |
| APOD | Astronomy Photo of the Day |
| APOD | Astronomy Picture Of the Day |
| APOLLO | Apache Point Observatory Lunar Laser-ranging Operation |
| APPLE | Ariane Passenger Payload Experiment |
| APS | Astronomy Planetary Science |
| APS | Astronomy & Planetary Science |
| APT | Astronomers Proposal Tools |
| APT | Astro-Photography Tool |