| Abbreviation | Definition |
|---|---|
| AEG | Astro Event Group |
| AER | Astronomy Education Review |
| AET | Accuracy Enhancing Technology |
| AFA | American Federation of Astrologers |
| AFO | Anonymous Flying Object |
| AGN | Active Galactic Nuclei |
| AGN | Active Galactic Nucleus |
| AGN | Active Galaxy Nucleus |
| AGPS | Assisted Global Positioning System |
| AGPS | Augmented Global Positioning System |
| AH | Asteroid Hunt |
| AIP | Astronomical Image Processing |
| AJD | Astronomical Julian Day |
| AL | Alternate Lifeform |
| AL | Astronomical League |
| ALAT | Airborne Large Aperture Telescope |
| ALFA | A Laser For Astronomy |
| ALIS | Airborne Laser Isotope Spectrometer |
| ALTS | Astronomy Lunch Time Seminar |
| AM | Anti Meridian |