 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 | — | — |