| C. E. K. Mees Observatory | Estados Unidos | Nueva York | — |
| Ca del Monte observatory | Italia | Pavía | — |
| CACTUS | Estados Unidos | — | 610 m |
| Cademuir Observatory | Irlanda | Dublín | — |
| Caimari observatory | España | Caimari | — |
| Cala d'Hort observatory | España | Es Cubells | — |
 Calais Observatory | Estados Unidos | Calais | — |
| Calar Alto TNO Survey | España | Gérgal | — |
| Calar Alto-CASADO observatory | España | — | — |
| Calar Alto-Schmidt observatory | España | — | — |
| Calarreona observatory | España | Murcia | — |
 Calf of Man Bird Observatory | Isla de Man | Isla de Man | — |
| Calgary observatory | Canadá | Calgary | — |
 Calorimetric Electron Telescope | — | — | — |
| Caloundra West observatory | Australia | Caloundra West | — |
 Calvin College Observatory | Estados Unidos | Grand Rapids | — |
| Calvin M. Hooper Memorial observatory | Estados Unidos | Hyde Park | — |
| Calvin-Rehoboth Robotic Observatory | Estados Unidos | Rehoboth | — |
| Camarillo observatory | Estados Unidos | California | — |
| Cambridge Bay Magnetic Observatory | Canadá | Cambridge Bay | — |
 Camille Flammarion Observatory | Francia | Juvisy-sur-Orge | — |
| Camorino observatory | Suiza | Camorino | — |
| Campo Catino Observatory | Italia | Guarcino | — |
| Campo dos Amarais observatory | Brasil | Lagoa Azul | — |
 Campo Imperatore Astronomical Observatory | Italia | L'Aquila | 2.129 m |
| Campocatino observatory | Italia | Collepardo | — |
| Campomaggiore observatory | Italia | Campo Maggiore | — |
| Can Roig observatory | España | Llagostera | — |
| Canberra Magnetic Observatory | Australia | — | — |
| Cancelada observatory | España | Estepona | — |
| Canopus Hill Observatory | Australia | Tasmania | — |
 Cantonal observatory of Neuchâtel | Suiza | Neuchâtel | 486 m |
| Canvas View New Mexico Skies observatory | Estados Unidos | Mayhill | — |
| CAO | Chile | San Pedro de Atacama | — |
| CAO | Chile | San Pedro de Atacama | — |
| Cape Clear Bird Observatory | Irlanda | Irlanda | — |
| Cape Verde Volcanological Observatory | Cabo Verde | — | — |
| Capilla Peak Observatory | Estados Unidos | New Mexico | — |
| Capricornus observatory | Hungría | Csókakő | — |
| Caraquiz Observatory | España | Caraquiz | — |
| Carbuncle Hill observatory | Estados Unidos | Greene | — |
| Carbuncle Hill Observatory | Estados Unidos | Coventry | — |
| Carda observatory | España | Villaviciosa | — |
| Cardiff observatory | Gales | Cardiff | — |
| Carina Observatory | Brasil | Sobradinho Esporte Clube | — |
 Carkeek Observatory | Nueva Zelanda | Distrito de Wairarapa del Sur | — |
| Carla Jane Observatory | Estados Unidos | Charlotte | — |
| Carmelita observatory | España | Tiana | — |
| Carpe-Noctem observatory | España | Navacerrada | — |
| Carpione Observatory | Italia | San Casciano in Val di Pesa | — |
| Carroll observatory | Estados Unidos | Condado de Santa Bárbara | — |
| Cartagena astronomical observatory | España | Canteras | — |
 Carter Observatory | Nueva Zelanda | Región de Wellington | — |
| Casal Lumbroso observatory | Italia | Roma | — |
| Casalecchio di Reno Observatory | Italia | Bolonia | — |
| Casasco observatory | Italia | Casasco | — |
| Cascade Mountain observatory | Estados Unidos | Cascade Mountain | — |
| Casellina observatory | Italia | Scandicci | — |
| Casey Station Magnetic Observatory | — | — | — |
| Casselman observatory | Canadá | Casselman | — |
| CAST Observatory | Italia | Talmassons | — |
| Castellon observatory | España | Castellón de la Plana | — |
| Castelmartini observatory | Italia | Castelmartini | — |
 Castillo de Abbadia | Francia | Hendaya | — |
 Castillo de Blackrock | Irlanda | County Cork | — |
| Castle Fields Observatory | Reino Unido | Calne | — |
| Castlemaine observatory | Australia | Castlemaine | — |
| Castrofilippo observatory | Italia | Castrofilippo | — |
| Cat's Eye observatory | Italia | Manciano | — |
| Catalina 40" Telescope | Estados Unidos | Pima County | 2.791 m |
 Catania Astrophysical Observatory | Italia | Catania | 1.735 m |
| Catania Astrophysical Observatory "A. Riccò" | Italia | Catania | — |
| Catholic University Observatory | Estados Unidos | Washington D. C. | — |
| Cavriana observatory | Italia | Cavriana | — |
 Cawthron Atkinson Observatory | Nueva Zelanda | Nelson | — |
| CBA Concord observatory | Estados Unidos | Tucson | — |
| CBA-East Observatory, Laurel | Estados Unidos | North Laurel | — |
| CBA-MM Observatory | Estados Unidos | Bass Lake | — |
| CBA-NOVAC Observatory, | Estados Unidos | Front Royal | — |
| CCAT Trieste observatory | Italia | Trieste | — |
| CEAM observatory | España | Caimari | — |
| CEAMIG-REA Observatory | Brasil | Belo Horizonte | — |
| Cedar Drive Observatory | Estados Unidos | Hofa Park | — |
| Cedar Glen Observatory | Estados Unidos | Lake Arrowhead | — |
| Cedar Knolls observatory | Estados Unidos | Municipio de Hanover | — |
| Celado, observatory | Italia | Castello Tesino | — |
| Celbridge Observatory | Irlanda | Celbridge Community School | — |
| Celestial Observatory | Estados Unidos | Arkansas | — |
| Celico observatory | Italia | Celico - Centro | — |
| Centennial Observatory | Estados Unidos | Twin Falls | — |
| Central Aerological Observatory | Rusia | Dolgoprudny | — |
| Centre d'astronomie de La Couyère | Francia | La Couyère | — |
| Centre for Basic Space Science and Astronomy | Nigeria | Nsukka | — |
 Centro Astronómico de Tiedra | España | Tiedra | — |
 Centro Astronómico de Toruń | Polonia | Torún | 94 m |
 Centro de Astronomia Espacial | España | — | — |
 Centro de Investigación Atmosférica de Izaña | España | Tenerife | — |
 Centro de Investigación en Astronomía, Astrofísica y Geofísica de Argel | Argelia | Argel | — |
 Centro de investigación en geodinámica y astrometría | Francia | Caussols | — |
 Centro Spaceguard de Bisei | Japón | Bisei | 427 m |
| Cereseto Observatory | Italia | Cereseto | — |
| Cerrina Tololo Observatory | Italia | Murisengo Monferrato | — |
| Cerro del Viento observatory | España | Badajoz | — |
| Cerro Pachón Observatory | Chile | — | — |
| Cerro Tololo-DECam | Chile | Piedras Blancas | — |
| Cerro Tololo-LCO A | Chile | Piedras Blancas | — |
| Cerro Tololo-LCO Aqawan A #1 | Chile | Piedras Blancas | — |
| Cerro Tololo-LCO Aqawan B #1 | Chile | Piedras Blancas | — |
| Cerro Tololo-LCO B | Chile | Piedras Blancas | — |
| Cerro Tololo-LCO C | Chile | Piedras Blancas | — |
| Cesaraugusto observatory | España | Zaragoza | — |
| Cesena Observatory | Italia | Casanova | — |
| Cesson observatory | Francia | Cesson | — |
| Cewanee Observatory at DSNM | Estados Unidos | New Mexico | — |
 Chabot Space and Science Center | Estados Unidos | Oakland | — |
| Chalandray-Canotiers observatory | Francia | Chalandray | — |
| Chambon la Foret Magnetic Observatory | Francia | — | — |
| Changchun Magnetic Observatory | República Popular China | — | — |
| Changchun Observatory | República Popular China | Changchun | — |
 Changgyeonggung Palace Gwancheondae | Corea del Sur | — | — |
 Chankillo | Perú | Casma | — |
| Chante-Perdrix observatory | Francia | Banon | — |
| Chapel Hill observatory | Estados Unidos | Texas | — |
| Charters Towers Magnetic Observatory | Australia | Queensland | — |
| Cheam observatory | Reino Unido | Municipio de Sutton | — |
| Chelford Observatory | Reino Unido | Chelford | — |
| Chelles observatory | Francia | Cantón de Chelles | — |
| Chelmsford observatory | Reino Unido | Chelmsford | — |
| Cheongyang Magnetic Observatory | Corea del Sur | — | — |
 CHEOPS | — | — | — |
 Cherenkov Telescope Array | — | — | — |
| Cherkizovo Observatory | Rusia | Cherkizovo | — |
| Cherokeeridge Observatory | Estados Unidos | Fort Madison | — |
| Cherryvalley Observatory | Irlanda | — | — |
| Chervishevo observatory | Rusia | Chervishevo | — |
| Chicharronian 3C Observatory | España | Tres Cantos | — |
| Chichibu Observatory | Japón | Chichibu | 800 m |
 Chico Community Observatory | Estados Unidos | California | — |
 Chilbolton Observatory | Reino Unido | Chilbolton | — |
| CHILESCOPE | Chile | — | — |
| CHILESCOPE Observatory | Chile | Río Hurtado | — |
| China-Iceland Arctic Science Observatory | Islandia | Þingeyjarsveit | — |
| Chinese Culture University observatory | República de China | Shilin District | — |
| Chinese Hα Solar Explorer | República Popular China | — | — |
| Chinese Virtual Observatory | República Popular China | — | — |
| Chinle observatory | Estados Unidos | condado de Apache | — |
| Chinon observatory | Francia | Chinon | — |
| Chions observatory | Italia | Chions | — |
 CHIPSat | — | — | — |
| Chiro Observatory | Australia | Yerecoin | — |
| Chirorin observatory | Japón | Otari | — |
| Chiusa di Pesio observatory | Italia | Chiusa di Pesio | — |
| Chomsongdae | Corea del Norte | Kaesong | — |
 Chorzow observatory | Polonia | Chorzów | — |
| Christiania observatory | Noruega | Oslo | — |
 Chuguevskaya Station Observatory | Ucrania | Raión de Chugúyev | 156 m |
| Chula Observatory | Estados Unidos | Chula | — |
| Church Stretton observatory | Reino Unido | Church Stretton | — |
 Cidnea Astronomic Observatory | Italia | Brescia | — |
| Cielo Profundo Observatory | España | Bercianos del Páramo | — |
 City Dome, City Observatory, Calton Hill, Edinburgh | Reino Unido | City de Edimburgo | — |
 City Observatory | Reino Unido | City de Edimburgo | — |
| Clarke Observatory | Estados Unidos | Ohio | — |
 Class of 1951 Observatory | Estados Unidos | — | — |
| Clavier observatory | España | Lora del Río | — |
| Clay Center Observatory, Brookline | Estados Unidos | Brookline | — |
| Clay Telescope observatory | Estados Unidos | Cambridge | — |
| Clayhole observatory | Finlandia | Jokela | — |
| Climenhaga Observatory | Canadá | Victoria | — |
| Clinton observatory | Estados Unidos | Maryland | — |
| Clixby Observatory | Reino Unido | North East Lincolnshire | — |
 Cloudcroft Observatory | Estados Unidos | New Mexico | 2.751 m |
| CMF astronomical observatory | Brasil | Paraná | — |
| CNVL Observatory | Rumania | Baia Mare | — |
| Coastal Observatory | Reino Unido | — | — |
 Coats Observatory | Reino Unido | Renfrewshire | — |
 COBE | — | — | — |
 Cobenzl observatory | Austria | Viena | — |
| Cobram observatory | Australia | Cobram | — |
| Cockfield observatory | Reino Unido | Cockfield | — |
| Cocos-Keeling Islands Magnetic Observatory | Australia | — | — |
| Coddenham Astronomical Observatory | Reino Unido | Coddenham | — |
 Cointe Observatory | Bélgica | Cointe | — |
| Colaba Observatory | India | — | — |
| Colchester observatory | Reino Unido | Colchester | — |
| Colegio Cristo Rey astronomical observatory | Argentina | Rosario | — |
| College Magnetic Observatory | Estados Unidos | — | — |
 Collins Observatory | Estados Unidos | Nueva York | — |
| Collonges observatory | Francia | Collonges | — |
| Colombo University Observatory | Sri Lanka | Colombo | — |
 Colonial Observatory | Nueva Zelanda | — | — |
| Comeglians observatory | Italia | Údine | — |
| Comet Hunter Observatory 2 | Estados Unidos | Pensilvania | — |
| Command Module Observatory | Estados Unidos | Tempe | — |
| Como observatory | Italia | Como | — |
 Complejo Astronómico El Leoncito | Argentina | Parque Nacional El Leoncito | 2.552 m |
| Compustar Observatory | Francia | Saint-Jacques-sur-Darnétal | — |
| Conder Brow observatory | Reino Unido | Carnforth | — |
| Conlin Hill Observatory | Estados Unidos | Oxford | — |
| Conrad Magnetic Observatory | Austria | — | — |
 Conrad Observatory | Austria | Muggendorf | — |
| Contern Observatory | Luxemburgo | Contern | — |
| Conway observatory | Estados Unidos | Conway | — |
| Copeland Bird Observatory | Reino Unido | — | — |
 Copernic Observatory | Bélgica | Provincia de Namur | — |
| Coralito observatory | España | San Cristóbal de La Laguna | — |
| Corcaroli Observatory | Italia | Malo | — |
| Cordell–Lorenz Observatory | Estados Unidos | Tennessee | — |
 Corfu Observatory | Grecia | Corfú | — |
| Corgas observatory | España | multa | — |
 Coriolis | Estados Unidos | — | — |
| Cormons observatory | Italia | Cormòns | — |
| Corner observatory | Alemania | Durmersheim | — |
 CORONAS-I | — | — | — |
 Corot | Francia | — | — |
| Corpus Christi observatory | Estados Unidos | Corpus Christi | — |
| Corralitos Observatory | Estados Unidos | New Mexico | — |
 COS-B | — | — | — |
 Cosmos 166 | — | — | — |
| Cosmos 230 | — | — | — |
| Cosmos Observatory | España | Anhingidae | — |
| Cosmos Research Center | Estados Unidos | California | — |
| Cosmos Sterrenwacht | Países Bajos | Dinkelland | — |
| Cosmosoz Observatory | Francia | Tassin-la-Demi-Lune | — |
| Costa Teguise observatory | España | Teguise | — |
 Cotobade Astronomical Observatory | España | Carballedo | 652 m |
| Cottonwood Observatory | Estados Unidos | Oklahoma | — |
| Courroux observatory | Suiza | Courroux | — |
| Couvaloup de St-Cergue observatory | Suiza | Saint-Cergue | — |
| CPF Observatory | Francia | Cantón de Saint-Vallier-de-Thiey | — |
| Cracow-Fort Skala observatory | Polonia | Cracovia | — |
 Crago Observatory | Australia | New South Wales | — |
| Craigie observatory | Australia | Craigie | — |
| Crane Observatory | Estados Unidos | Kansas | — |
 Crawford Observatory | Irlanda | — | — |
| Crawfordville Observatory | Estados Unidos | Sharon | — |
| Creighton University Observatory | Estados Unidos | Nebraska | — |
| Crescent Moon Observatory | Estados Unidos | Cristóbal Colón | — |
| Crespadoro observatory | Italia | Crespadoro | — |
| Crimean Laboratory of Sternberg Astronomical Institute | Ucrania | Nauchnyi | 600 m |
 CRISTA-SPAS I | — | — | — |
 CRISTA-SPAS II | — | — | — |
| Cristiansø Feltstation | Dinamarca | — | — |
 Crohamhurst Observatory | Australia | Queensland | — |
| Crolles observatory | Francia | Crolles | — |
| Crow Observatory | Portugal | Sète | — |
 Crow Observatory | Estados Unidos | Misuri | — |
| Cruz del Sur observatory | Argentina | San Justo | — |
| CS3-DanHenge Observatory | Estados Unidos | Landers | — |
| CS3-Palmer Divide Station | Estados Unidos | Landers | — |
| CS3-Trojan Station | Estados Unidos | Landers | — |
| Cupillari Observatory | Estados Unidos | Pensilvania | — |
| Cupola minore est dell'Osservatorio Astronomico | Italia | Merate | — |
| Cupola minore ovest dell'Osservatorio Astronomico | Italia | Merate | — |
| Cupola principale telescopio Ruths dell'Osservatorio Astronomico | Italia | Merate | — |
| Cupola telescopio Zeiss dell'Osservatorio Astronomico | Italia | Merate | — |
| Curdridge observatory | Reino Unido | Curdridge | — |
 Custer Observatory | Estados Unidos | Nueva York | — |
| Cuteip Remote Observatory | República de China | Condado de Changhua | — |
 CWU Observatory | Estados Unidos | Ellensburg | — |
 CWU-Lind Observatory | Estados Unidos | Ellensburg | — |
| Cyclops observatory | Países Bajos | Oost-Cappel | — |
| Cygnus Observatory | Reino Unido | New Alresford | — |
 Cámara Oscura, Edimburgo | Reino Unido | City de Edimburgo | — |
 Cégep de Trois-Rivières Observatory | Canadá | Champlain | — |
 ÇOMÜ Ulupınar Observatory | Turquía | — | 410 m |