| 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 | — |