| "Johann Kepler" Astronomical Observatory at "Vasil Levski" Secondary School | Bulgaria | Troyan | — |
 "Terrazza delle Stelle" observatory | Italia | Trento | — |
| 's-Gravenwezel Observatory | Bélgica | Amberes | — |
| 150-foot solar tower | Estados Unidos | — | — |
| 1st Moscow Gymnasium Observatory | Rusia | Moscow Oblast | 218 m |
| 29PREMOTE Observatory | Francia | Banon | — |
| 6ROADS Observatory | Polonia | Wojnówko | — |
| 6ROADS Observatory 2 | España | Nerpio | — |
| 7300 observatory | Estados Unidos | Mayhill | — |
| A. Volta observatory | Italia | Lanzo d'Intelvi | — |
 A.C. Barnes Observatory | Estados Unidos | Ithaca | — |
| AAS Montsec observatory | España | Lérida | — |
| Abbey Ridge Observatory | Canadá | Stillwater Lake | — |
| Abbeydale Observatory | Reino Unido | Gloucester | — |
| Abisko Magnetic Observatory | Suecia | Abisko | 380 m |
| ABObservatory, Rosarno | Italia | Rosarno | — |
 ABRIXAS | — | — | — |
 Abu Rayhan al-Biruni Observatory | Irán | — | — |
 Academia Naval de los Estados Unidos | Estados Unidos | Maryland | — |
| Achternholt observatory | Alemania | Wardenburg | — |
| Ad Astra Sangos Observatory | España | Alhendín | — |
| Adati observatory | Japón | Minamisōma | — |
| Addis Ababa Magnetic Observatory | Etiopía | Adís Abeba | — |
| Adena Brook Observatory | Estados Unidos | Columbus | — |
| Adhara obsevatory | Brasil | Law School of Sorocaba | — |
 Admiral Vasile Urseanu House, Bucharest | Rumania | Bucarest | — |
| Adolphson Observatory | Estados Unidos | Monmouth | 232 m |
 Advanced Composition Explorer | Estados Unidos | — | — |
 Advanced Telescope for High Energy Astrophysics | — | — | — |
| Advanced X-Ray Imaging Satellite | Estados Unidos | — | — |
| AG_Sarajevo Observatory | Bosnia y Herzegovina | Sarajevo | — |
| Ageo observatory | Japón | Ageo | — |
| Ager observatory | España | Ager | — |
 Ager observatory | España | Ager | — |
 Ager observatory, Lleida | España | Lérida | — |
 AGILE | Italia | — | — |
| AGM Observatory | Marruecos | Marrakech | — |
| AGP GUAM 4 observatory | España | Málaga | — |
 Agrupación Astronómica de Sabadell | España | Sabadell | — |
| AHS Observatory | Estados Unidos | Castaic | — |
| Aichtal observatory | Alemania | Aichtal | — |
 Air Force Maui Optical and Supercomputing observatory | Estados Unidos | Maui County | — |
| Airali Observatory | Italia | Turín | — |
 Airdrie Public Observatory | Reino Unido | North Lanarkshire | — |
| Akashina observatory | Japón | Akashina | — |
| Akeno Giant Air Shower Array | Japón | Akeno | — |
| Akeno Observatory | — | — | — |
| Akou observatory | Japón | Akō | — |