All
- Pulsar Characteristic Age
- Pulsar Dispersion Measure
- Pulsar Evolution
- Pulsar Timing
- Quark
- Quasar
- 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
- S0 Galaxy
- Scale Height
- Scale Length
- Scaling Relations
- Scattered Disk Objects
- Schwarzschild Lens
- Schwarzschild Radius
- Seasons
- Second
- Secular Evolution
- Self-gravitating Bodies
- Self-gravitation
- Semi-major Axis
- Semi-minor Axis