Answer:
Absolute magnitude. Two stars of the same absolute magnitude usually do not have the same apparent magnitude because one may be much farther from us than the other. The other that is farther away will appear dimmer. To compare absolute brightness, astronomers determine what magnitude the stars would have if they were at a standard distance of about 32.6 light years. The sun has an apparent magnitude of -26.7, if located at a distance of 32.6 light years, have an absolute magnitude of 5. Stars with absolute magnitude values lower than 5 are brighter than the sun. Because of their distance, however, they appear much dimmer.