The BRIGHTEST stars, are called FIRST magnitude. Stars that appear half as bright are SECOND magnitude, those dimmer still are THIRD, etc.
On such a scale, the LARGER the number, the DIMMER the star. Objects BRIGHTER than the brightest 1st magnitude stars, are expressed as negative values. The Sun is m = -27 (see below).
Each magnitude corresponds to a factor of 2.5 in brightness (observed flux). An object that is brighter by two magnitudes is 2.5 x 2.5 = 6.3 times brighter, an object that is brighter by three magnitudes is 2.5 x 2.5 x 2.5 = 16 times brighter, and so on..
APPARENT MAGNITUDE: is a way of comparing the brightness of objects based on what we see on Earth, with no regard to how far away the source may be. This measurement is symbolized by a lower case, m.
| Dimmest star seen by the Hubble Space Telescope | 30.0 |
| Dimmest star seen with an amateur telescope | 15.0 |
| Dimmest star the human eye can see | 6.0 |
| Brightest star in the sky (Sirius) | -1.5 |
| Venus at its brightest | -4 |
| Brightness of the Full Moon | -11 |
| Brightness of the Sun | -27 |
ABSOLUTE MAGNITUDE: the magnitude of an object, assuming it is placed at a distance of 10 parsecs (about 32 light years). This is thus a measure of an intrinsic property of the star or object, and is thus a distance-independent measurement. This measurement is symbolized as an upper case, M.