IB HL astrophysics option
Constellation
No physical relation between stars, however form a distinguishable pattern
Stellar cluster
Group of close stars, formed from collapsed gas cloud. Held together by gravity
Galaxy
Large collections of thousands of stars held together by gravity
Luminosity
Energy emitted by a star per second
Apparent brightness
The energy received per second per unit area
White dwarfs
Hot, not very bright formed when mass is less than chandresaker limit
Giants
Cool star, high energy
Cepheid variable star
Star that is unstable undergoing periodic expansion and contraction. Apparent brightness fluctuates
apparent magnitude
the brightness of a celestial object as it appeared from earth
Absolute magnitude
the brightness of a star measured from a distance of 10 parsecs
binary stars
Pairs of stars that orbit each other in the same region of space. Also same distance. Visual rotate around each other. Spectroscopic binaries shift away and towards earth causing varying doppler shift
hubbles law
recessional speed of a galaxy is directly proportional to the distance of a galaxy