| Abbreviation | Definition |
|---|---|
| CIP | Celestial Intermediate Pole |
| CM | Critical Mass |
| CMA | Canis Majoris A |
| CMB | Cosmic Microwave Background |
| CMBR | Cosmic Microwave Background Radiation |
| CMDA | Celestial Mechanics and Dynamical Astronomy |
| CME | Coronal Mass Ejections |
| CMF | Core Mass Function |
| CMHAS | Crayford Manor House Astronomical Society (UK) |
| CMHASD | Crayford Manor House Astronomical Society Dartford |
| CMT | Carlsberg Meridian Telescope |
| CNS | Central Navigation System |
| COACA | Center Of Ancient Chinese Astronomy |
| COD | Carbon Oxygen Dwarf |
| CODE | Creation Out of Deep Energy |
| CoSEC | Collaborative Sun-Earth Connector |
| COT | Check-Out on Type |
| CP | Cambridge Pulsar |
| CRAF | Committee on Radio Astronomy Frequencies |
| CRAP | Completely Radical Anthropic Principle |