| 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 | — |