| 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 | — |
| Al Sadeem Observatory | Emiratos Árabes Unidos | Abu Dhabi | — |
| Al-Fulaij observatory | Omán | Al Batinah Sur gobernación | — |
| Al-Khatim Observatory | Emiratos Árabes Unidos | Abu Dhabi | — |
 Al-Khawarizmi Astronomy Complex | Malasia | — | — |
| Al-Ujairi Observatory | — | — | — |
| Alasht Amateur Observatory | — | — | — |
| Albanyà Observatory | España | Albañá | — |
 Alberto do Mónaco observatory | Portugal | — | — |
| Albigneux observatory | Francia | Saint-Héand | — |
| Albireo Observatory | España | Inca | — |
| Albox observatory | España | San Roque | — |
| Alder Springs observatory | Estados Unidos | Alder Springs | — |
| Alderney Bird Observatory | Guernsey | Alderney | — |
 Aldershot Observatory | Reino Unido | Rushmoor | — |
| Alert Magnetic Observatory | Canadá | Nunavut | 60 m |
 Alexander-Frantz-Sternwarte | Alemania | Dresde | — |
| Algarve Observatory | Portugal | Portimão | — |
| Alginet Observatory | España | Alginet | — |
| Ali Observatory | República Popular China | Ngari | 5.047 m |
| Alianza S4 observatory | Argentina | Departamento Calingasta | — |
| Alibag Magnetic Observatory | India | Maharashtra | 0 m |
| Alicante observatory | España | El Campello | — |
| Alice Springs Magnetic Observatory | Australia | Northern Territory | 557 m |
| Aljaraque Observatory | España | Aljaraque | — |
| Allahabad Observatory | — | — | — |
| Allen observatory | Estados Unidos | Bob Dylan | — |
| Allgäuer Volkssternwarte Ottobeuren | Alemania | Ottobeuren | 696 m |
| Alma Ata Magnetic Observatory | Kazajistán | — | 1.300 m |
| Almalex Observatory | Reino Unido | Ciudad de Leeds | — |
| ALMO observatory | Italia | Padulle | — |
| Alnitak observatory | España | El Puerto de Santa María | — |
| ALOMAR | Noruega | Andøy | — |
 Alor Setar Tower | Malasia | Alor Setar | — |
| Alphard Observatory | Italia | Satia | — |
 Alston Observatory | Reino Unido | Longridge | — |
| Alt emporda Observatory | España | Urdanta | — |
| Altamira observatory | Canarias | Aguerche | — |
| Altdorf Observatory | Alemania | Altorf | — |
 Alte Sternwarte | Alemania | Stadtbezirk Bonn | — |
 Alte Sternwarte | Alemania | Münster | — |
| Altenburg observatory | Alemania | Altemburgo | — |
| Alter Satzberg observatory | Austria | Viena | — |
| Althuraya Astronomy Center | Emiratos Árabes Unidos | Dubái | — |
| Altimira observatory | Estados Unidos | Coto de Caza | — |
 Altitude SEE Test European Platform | Francia | — | 2.252 m |
| Alto Turia astronomical center | España | — | — |
| Altrincham observatory | Reino Unido | Trafford | — |
| Altschwendt observatory | Austria | Altschwendt | — |
| Amanecer de Arrakis observatory | España | Alcalá de Guadaíra | — |
| Ametlla del Valles observatory | España | Can Reixac (Sant Gregori) | — |
 Amphi Ashdod Observatory | Israel | Ashdod | — |
| An Carraig Observatory | Reino Unido | Newry | — |
| Ananjev observatory | Ucrania | Raión de Ananiv | — |
 Ancien observatoire astronomique de la Marine de Nantes | Francia | Nantes | — |
| Andean Northern observatory | Finlandia | Nummi-Pusula | — |
| Andromeda Astronomical Observatory | Bulgaria | Stolichna obshtina | — |
| Andromeda Observatory | Hungría | Miskolc | — |
| Angel Peaks observatory | Estados Unidos | Creek | — |
 Angell Hall Observatory | Estados Unidos | Míchigan | — |
 Aniane astronomical observatory | Francia | Aniane | — |
| Antananarivo Magnetic Observatory | Madagascar | — | — |
| Antananarivo Observatory | — | — | — |
 Antares Astronomical Observatory | Brasil | Feira de Santana | — |
| Antares MTM Observatory | Italia | San Donato Val di Comino | — |
| Antares observatory | Argentina | Provincia de Buenos Aires | — |
| Antelope Hills Observatory | Estados Unidos | Bennett | — |
| Antibes observatory | Francia | Antibes | — |
 Antiguo Observatorio de Moscú | Rusia | Presnensky District | — |
| Antikythira Bird Observatory | Grecia | Kythira Municipality | — |
 Antonín Bečvář observatory | República Checa | Most | 395 m |
| Anunaki Observatory | España | Rivas-Vaciamadrid | — |
| Anwar Damha observatory | Brasil | São Paulo | — |
| Anysllum observatory | España | Ager | — |
| Anzio observatory | Italia | Lavinio Lido di Enea | — |
| Aorangi Iti Observatory | Nueva Zelanda | — | — |
| Apex observatory | Estados Unidos | Carolina del Norte | — |
| Apia Magnetic Observatory | Samoa | — | 2 m |
| Apollo Observatory | Estados Unidos | Dayton | — |
 Apollo Telescope Mount | — | — | — |
| Appledorne Observatory | Reino Unido | Farnsfield | — |
| Aqaba Bird Observatory | Jordania | Gobernación de Aqaba | — |
| Aravaca Observatory | España | Madrid | — |
| Arbonne la Foret observatory | Francia | Arbonne-la-Forêt | — |
 ARCADE | — | — | — |
| Arcadia observatory | Australia | Arcardia Gas Field | — |
| Arcangel observatory | España | Las Zocas | — |
 Archeops | — | — | — |
| Arcturus Observatory | Estados Unidos | Municipio de Manchester | — |
| Area 52 Observatory | Estados Unidos | Nashville | — |
| AREA31 Radio Observatory | Canadá | Shelburne | — |
| Arenal-Miravalles Seismological and Volcanological Observatory | Costa Rica | — | — |
| Argelander Institute for Astronomy observatory | Alemania | Bonn | — |
| Argentine Island Magnetic Observatory | — | — | — |
| Argus Array | Estados Unidos | Texas | — |
| Arizona Radio Observatory | Estados Unidos | Arizona | — |
| Arkansas Sky Observatory, Petit Jean Mountain South | Estados Unidos | Petit Jean Mountain | — |
| 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 | — |
 Astronomical observatory | Italia | Monte Porzio Catone | 401 m |
| Astronomical Observatory A.L. Kekin | Rusia | Kekin High School | 100 m |
 Astronomical Observatory and Planetarium "Nicolaus Copernicus" | Bulgaria | Municipio de Varna | 14 m |
| Astronomical Observatory and Planetarium - Yambol | Bulgaria | Yambol | — |
| Astronomical Observatory at the Youth Center - Haskovo | Bulgaria | Haskovo | — |
| Astronomical Observatory Cosmos Dome | Japón | Prefectura de Yamagata | — |
 Astronomical Observatory Dietrich Schiel | Brasil | São Carlos | — |
| Astronomical observatory et planetarium in San Giovanni | Italia | San Giovanni in Persiceto | — |
 Astronomical observatory Gabrovo | Bulgaria | Gabrovo | — |
| Astronomical Observatory in Alto da Sé | Brasil | Pernambuco | — |
| Astronomical Observatory in Kolonitskom plateau | Eslovaquia | — | — |
 Astronomical Observatory in Tradate | Italia | Tradate | — |
| Astronomical observatory Leipzig | Alemania | Leipzig | — |
 Astronomical observatory Manfred von Ardenne | Alemania | Dresde | — |
| Astronomical Observatory named after Professor Robert Głębocki | Polonia | Gdansk | — |
 Astronomical Observatory of Abruzzo | Italia | Teramo | 390 m |
| Astronomical Observatory of Capannoli | Italia | Capannoli | — |
| Astronomical observatory of Castelgrande | Italia | Castelgrande | — |
| Astronomical Observatory of Farra d'Isonzo | Italia | Farra d'Isonzo | — |
 Astronomical Observatory of Kharkov National University | Ucrania | Járkov | — |
| Astronomical Observatory of Kyiv Shevchenko National University | Ucrania | Óblast de Kiev | 156 m |
 Astronomical Observatory of Kyiv University | Ucrania | Kiev | — |
 Astronomical Observatory of Lviv University | Ucrania | Leópolis | — |
 Astronomical Observatory of Paraíba | Brasil | Paraíba | — |
 Astronomical Observatory of Saratov State University | Rusia | Sarátov | — |
| Astronomical Observatory of Shumen university | Bulgaria | Shumen | 493 m |
 Astronomical observatory of Siena observatory | Italia | Siena | — |
 Astronomical Observatory of the Infante D. Luís Geophysical Institute | Portugal | Santo António | — |
 Astronomical Observatory of the Jagiellonian University | Polonia | Voivodato de Pequeña Polonia | — |
| Astronomical Observatory of the National University of Asuncion | Paraguay | Asunción | — |
 Astronomical Observatory of the University of Kazan | Rusia | Kazán | — |
| Astronomical Observatory of the University of the Punjab | Pakistán | — | — |
 Astronomical Observatory of Trieste | Italia | Trieste | — |
 Astronomical Observatory of Vilnius University | Lituania | Vilna | 101 m |
| Astronomical Observatory St. Petersburg State University | Rusia | San Petersburgo | 20 m |
| Astronomical Observatory University of Siena | Italia | Siena | — |
| Astronomical Research Observatory, Charleston | Estados Unidos | Charleston | — |
| Astronomical Research Westfield observatory | Estados Unidos | Westfield | — |
| Astronomical Society Višnjan | — | — | — |
 Astronomical station at North Caucasus of Kazan Federal University | Rusia | Arjyz | — |
| Astronomical Station Vidojevica | Serbia | Beli Kamen | — |
 Astronomical Tower in Clementinum Prague | República Checa | Praga 1 | — |
| Astronomihagen observatory | Noruega | Vormstad | — |
 Astronomische Nederlandse Satelliet | — | — | — |
 Astronomische Station „Tycho Brahe“ | Alemania | — | — |
 Astronomisches Zentrum Schkeuditz | Alemania | Schkeuditz | — |
| Astronomy Centre | Reino Unido | Todmorden | — |
 Astronomy Club of Kosova | Kosovo | Pristina | — |
 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 | — | — |
| Ähtäri Observatory | Finlandia | Ähtäri | — |