Physics: Astrophysics Vocabulary Definitions
Light year
The distance travelled by light in one year.
Luminosity
The amount of energy radiated by a star per second.
Apparent brightness
The received energy per second per unit area of a detector (on earth).
Parsec
The distance to a star whose parallax is one arcsecond.
Apparent magnitude
A measure of how bright an object appears (from Earth)
Absolute magnitude
The apparent magnitude a star would have if placed at a distance of 10 pc from earth.
Critical density
The density of the Universe at which the Universe expands forever at a slowing rate approaching zero.