The second way stars are classified is by brightness, or absolute
magnitude. Absolute magnitude depends on the energy output of a
star. Brighter stars release more energy. A problem with this
classification is that a very bright star that is far away looks less
bright than a dim star that is close by (relative brightness).
This issue is fixed by mathematically comparing the brightness of
stars as if they were all the same distance from Earth. The chart
below shows some examples of stars and their absolute magnitudes. Note
that the lower number indicate brighter stars.
How much brighter is Spica than our Sun?