| Arkyd-6A | Estados Unidos | — | — |
| Armilla observatory | España | esfera armilar | — |
 Array of Low Energy X-ray Imaging Sensors | — | — | — |
| Arroyo Observatory | España | Miguel Arroyo Hurtado | — |
| ART observatory | España | Fregenal de la Sierra | — |
| Arta Geophysical Observatory | Yibuti | — | — |
| Artemis Observatory | España | Parque Nacional del Teide | — |
| Arti Magnetic Observatory | Rusia | — | — |
 Asahikawa observatory | Japón | Asahikawa | — |
 Asahikawa Science Center "Sci-Pal" | Japón | Asahikawa | — |
 Asama Volcano Observatory | Japón | — | 1.406 m |
| ASC-Kislovodsk observatory | Rusia | Karacháyevo-Cherkesia | — |
| Ascension Island Magnetic Observatory | Reino Unido | Ascension | 177 m |
| Ascot observatory | Reino Unido | Ascot | — |
 Ashton Observatory | Estados Unidos | Iowa | — |
| Aso Volcanological Laboratory | Japón | Minamiaso | — |
| Asociacion Astronomica de Cartagena | España | Canteras | — |
 Asociación Argentina Amigos de la Astronomía | Argentina | Buenos Aires | — |
 Asociación Entrerriana de Astronomía | Argentina | — | — |
| Assonet observatory | Estados Unidos | Assonet | — |
 Assy-Turgen Observatory | Kazajistán | provincia de Almatý | 2.750 m |
| ASTEP, Concordia Station | — | Base Concordia | — |
 ASTERIA | Estados Unidos | — | — |
| Asterion Observatorium | Rusia | Petrozavodsk | 143 m |
| Astreo Observatory | España | Mairena del Aljarafe | — |
| Astro | — | — | — |
| Astro Dolomites observatory | Italia | Provincia autónoma de Bolzano | — |
| ASTRO-A | Japón | — | — |
 ASTRO-C | — | — | — |
 ASTRO-E | — | — | — |
 ASTRO-E | — | — | — |
 ASTRO-F | — | — | — |
 Astroblème Charlevoix observatory | Canadá | La Malbaie | — |
| Astrocamp Manciano Observatory | Italia | Manciano | — |
| AstroCamp observatory | España | Nerpio | — |
| AstroColauri observatory | Italia | Nápoles | — |
| Astrognosis Observatory | Reino Unido | Bradwell | — |
| Astrolab | Bélgica | — | — |
 Astron | Unión Soviética | — | — |
 Astronaut Memorial Planetarium and Observatory | Estados Unidos | Florida | — |
 Astronomic Observatory in Włocławek | Polonia | — | — |
| Astronomical and Geophysical Observatory in Golovec | Eslovenia | Liubliana | 410 m |
| Astronomical Center of Shumen University | Bulgaria | Shumen | — |
 Astronomical Center Rijeka | Croacia | — | — |
| Astronomical Institute | Rusia | — | — |
| Astronomical League Alpha observatory | Estados Unidos | Portal | — |
 Astronomical observatory | Eslovaquia | Prešov | — |
 Astronomical Observatory | Estados Unidos | Urbana | — |