 Astronomy Station "Samuel Heinrich Schwabe" | Alemania | Dessau-Roßlau | — |
| Astrophoton observatory | Austria | Audorf | — |
| Astrophysical Multimessenger Observatory Network | — | — | — |
| Astrophysical Observatory of the College of Staten Island | Estados Unidos | Nueva York | — |
 Astrophysical Virtual Observatory | — | — | — |
 Astrosat | India | — | — |
| Astroshot Observatory | Irlanda | Derry | — |
 AstroVal | Suiza | — | — |
| AstroVal observatory | Suiza | Le Chenit | — |
| Atacama Desert Observatory | Chile | San Pedro de Atacama | — |
| Athabasca University Geophysical Observatory | Canadá | Athabasca | — |
| Atlante observatory | España | Santa Cruz de Tenerife | — |
 ATLAS | — | — | — |
| Atlas Golf Marrakech | Marruecos | Marrakech | — |
| ATLAS-MLO Auxiliary Camera | Estados Unidos | Waiākea-Uka | — |
| ATLAS–CHL observatory | Chile | Río Hurtado | 1.570 m |
| ATLAS–HKO observatory | Estados Unidos | Maui County | 3.030 m |
| ATLAS–MLO observatory | Estados Unidos | Hawaii County | 3.408 m |
| ATLAS–SAAO observatory | Sudáfrica | Karoo Hoogland | 1.767 m |
| ATLAS–TDO observatory | España | Tenerife | 2.370 m |
| ATU Astronomical Observatory | Estados Unidos | Russellville | — |
| Augerolles observatory | Francia | Augerolles | — |
| Auroral Observatory | Noruega | Tromsø | — |
 Australia Telescope National Facility | Australia | New South Wales | — |
 Australian Astronomical Observatory | Australia | New South Wales | 1.164 m |
| Automatic Geophysical Observatory | — | — | — |
| Ayabe City Astronomical Museum | Japón | Ayabe | — |
| Ayabe observatory | Japón | Ayabe | — |
| AZM Martinsberg observatory | Austria | — | — |
| Bacau Observatory | Rumania | Bacău | — |
 Badalona Boreal observatory | España | Badalona | — |
| Badalona observatory | España | Badalona | — |
| Badalozhnyj observatory | Rusia | Krasnoyarsk Krai | — |
 Badlands Observatory | Estados Unidos | Quinn | — |
| Bagdad observatory | Estados Unidos | Bagdad | — |
| Bagnall Beach Observatory | Australia | New South Wales | — |
 Baikal Astrophysical Observatory | Rusia | Listvianka | 645 m |
| Baja Astronomical Observatory | Hungría | Baja | — |
| Baker Lake Magnetic Observatory | Canadá | Nunavut | — |
| Baker Observatory | Estados Unidos | Misuri | — |
| Bakersfield observatory | Estados Unidos | Bakersfield | — |
 Baksan Neutrino Observatory | Rusia | — | — |
| Baksan Underground Scintillation Telescope | — | — | — |
| Balbriggan Observatory | Irlanda | Balbriggan | — |
 Baldone Observatory | Letonia | Baldone Parish | 80 m |
| Ball State University Observatory | Estados Unidos | Indiana | — |
| Balzaretto Observatory | Italia | Roma | — |
| Bamberg observatory | Alemania | Bamberg | — |