A
| Name | Established | Location |
| Abastumani Astrophysical Observatory | 1932 | Abastumani, Georgia |
| Abu Reyhan-e Birooni Observatory | 1976 | Shiraz University, Shiraz, Iran |
| Advanced Composition Explorer (ACE) | 1997 | Earth–Sun L1 point |
| Aker Observatory | 1995 | Safford, Arizona, USA |
| Aldershot Observatory | 1906 | Aldershot, Hampshire, England |
| Algonquin Radio Observatory | 1959 | Algonquin Provincial Park, Ontario, Canada |
| Allegheny Observatory | 1859 | Pittsburgh, Pennsylvania, USA |
| Ametlla de Mar Observatory | 1992 | l'Ametlla de Mar, Catalonia, Spain |
| AMiBA | 2006 | Mauna Loa, Hawaii, USA |
| Anderson Mesa Station | 1959 | Flagstaff, Arizona, USA |
| Angell Hall Observatory | 1927 | Ann Arbor, Michigan, USA |
| Antarctic Muon and Neutrino Detector Array | 2002 | Antarctica |
| Antarctic Submillimeter Telescope and Remote Observatory | 1994–2005 | Antarctica |
| Apache Point Observatory | Sunspot, New Mexico, USA | |
| Apatity Cosmic-Ray Station | Apatity, Russia | |
| Apollo Observatory | 1969 | Dayton, Ohio, USA |
| Arcetri Observatory | Arcetri, Florence, Italy | |
| Arecibo Observatory | 1963 | Arecibo, Puerto Rico, USA |
| Armagh Observatory | 1790 | Armagh, United Kingdom |
| Aryabhatta Research Institute of Observational Sciences | 1954 | Nainital, Uttarakhand, India |
| Ashton Observatory | 1983 | Baxter, Iowa, USA |
| Asiago Observatory | 1942 | Asiago, Italy |
| Astron (defunct) | 1983–1989 | Highly eccentric Earth orbit |
| Astronomical Observatory of Lisbon | 1867 | Lisbon, Portugal |
| Astrophysical Institute Potsdam | 1992 | Potsdam, Germany |
| Atacama Pathfinder Experiment (APEX) | 2003 | Llano de Chajnantor Observatory, Chile |
| Australia Telescope Compact Array | 1988 | Narrabri, Australia |
| Australian Astronomical Observatory | 1971 | Coonabarabran, Australia |
Read more about this topic: List Of Astronomical Observatories