R
- Radial velocity
- Radian
- Radiant
- Radiant Flux Density
- Radiation Pressure
- Radio Astronomy
- Radio Interferometer
- Radio Supernova
- Ram Pressure Stripping
- Rayleigh Criterion
- Real Image
- Recurrent Novae
- Red Dwarf
- Red giant stars
- Redshift
- Reflection Nebula
- Relativistic Cosmology
- Resolution
- Right Ascension
- Roche-lobe
- Roche-lobe Overflow
- Roemer Delay
- Rotation Curve
- RR Lyrae
- RRATs