
Stars can be classified in three ways:
 Size – How massive the star is
 Temperature – A stars color reveals its temperature.
▪ Red stars have a cooler temperature, and blue stars have a
warmer temperature.
 Brightness/Magnitude – The amount of light a star
gives off depends on its size and temperature.

How bright a star looks from Earth depends
upon both how far the star is from Earth and
how bright the star actually is.

A stars brightness can be can be described in
two ways: apparent magnitude and absolute
magnitude.

Apparent magnitude is the brightness of a
star as seen from Earth.

Absolute magnitude is brightness of a star as
if it were 32.6 light years from Earth.
 The brightness of the stars is compared to the
brightness of our Sun. We call this luminosity.

An HR diagram shows the two most
important characteristics of stars, which are
temperature and absolute magnitude
(brightness) and/or luminosity.

Scientists plot the surface temperatures of
stars and their brightness on a graph.