peri - phot
- periapsis
- periastron
- pericenter
- perigee
- perihelion
- period
- period age relation
- period change
- period color relation
- period density relation
- period determination
- period luminosity color relation
- period luminosity relation
- period mass relation
- period radius relation
- period spectrum relation
- period variation
- periodic comets
- periodic orbits
