| Apex of the Sun's Path | The Apex of the Sun's Path: A Stellar I… | Stellar Astronomy |
| Aphelion | At the Farthest Reach: Understanding Ap… | Stellar Astronomy |
| Aphelion | Aphelion: The Distant Dance of Planets … | Galactic Astronomy |
| Apian, Peter Bienewitz | Peter Apian: The Man Who First Recogniz… | Astronomers |
| Aplanatic | Achieving Clarity: The Quest for Aplana… | Galactic Astronomy |
| Apoastron or Aphastron | Apoastron: The Point of Maximum Separat… | Galactic Astronomy |
| Apogean | Reaching the Highest Point: Understandi… | Stellar Astronomy |
| Apogee | Reaching the Zenith: Understanding Apog… | Stellar Astronomy |
| Apogee | Reaching for the Stars: Understanding A… | Galactic Astronomy |
| Apollonius | Apollonius of Perga: The Mathematician … | Astronomers |
| Apparent Ellipse | The Apparent Ellipse: Unveiling the Dan… | Galactic Astronomy |
| Apparent Magnitude | The Brilliance of Stars: Understanding … | Stellar Astronomy |
| Apparent Motion | The Dance of the Stars: Understanding A… | Stellar Astronomy |
| Apparent Sun | The Sun's Many Faces: Understanding the… | Galactic Astronomy |
| Apparition, Circle of Perpetual | The Circle of Perpetual Apparition: Unv… | Galactic Astronomy |
| Appulse | Appulse: When Celestial Bodies Get Cozy… | Galactic Astronomy |
| Apse, or Apsis | The Ups and Downs of Orbits: A Guide to… | Galactic Astronomy |
| Apsides, Line of | The Dance of the Apsides: Understanding… | Galactic Astronomy |
| Apsis | The Dance of the Stars: Understanding A… | Stellar Astronomy |
| Apus (the Bird of Paradise) | Apus: The Bird of Paradise in the South… | Constellations |
