What Is Absolute Magnitude and How Do Astronomers Measure a Star’s Absolute Magnitude?

When we look at stars, the closer ones usually appear brighter than the ones farther away.

Absolute magnitude is how bright each star would look if they were all 10 parsecs, or 33 light-years away.

For instance, the Sun appears to be the brightest star. It has an apparent magnitude of -27.72. Altair appears about sixty-five times fainter than the Sun, with an apparent magnitude of 0.77.

But if both stars were 10 parsecs away, the Sun’s magnitude would be 4.8 and Altair’s would be 2.3.

The Sun’s absolute, or true, magnitude is 7.5 times fainter than Altair’s.

Remember that higher magnitude numbers mean fainter stars.