| Term: | Apparent magnitude |
| Definition: |
A measure of a star's observed brightness (opposed to absolute magnitude); symbol m. It depends on the star's intrinsic brightness, its distance from the observer, and the amount of interstellar absorption. The brightest star Sirius has an apparent magnitude of -1.46, while the weakest stars visible with the naked eye in the most favorable observation conditions have magnitudes of about +6.5. The stars of magnitudes less than +23 are measured by professional observatories, whereas those of magnitudes less than +30 by a telescope such as the Hubble Space Telescope. |