Star Classification
Stars are classified by their spectra (the
elements that they absorb) and their
temperature. There are seven main
types of stars; in order of decreasing
temperature, O, B, A, F, G, K, and M. The
temperature of each spectral class is
then further subdivided from hot to
cool by the simple addition of a
number, where 0 is the hottest and 9
the coolest. The Sun is considered a G-
class star.
Red hot and cool ice blue – NOT! We are
accustomed to referring to things that
are red as hot and those that are blue
as cool. In fact though, heated objects
change colour as their temperature
changes and red represents the lowest
temperature at which a heated object
can glow in visible light. As it gets
hotter, the colour changes to white and
ultimately to blue. So the red stars you
see in the sky are the “coolest” (least
hot), and the blue stars are the hottest!