# Magnitude

Magnitude is a unit of measure for the brightness (or visibility) of stellar object.

## Description (Specifications)

Absolute magnitudes for stars generally range from -10 to +17.

There are two kinds of magnitude:

1. Apparent Magnitude (m) which measures the brightness of a stellar object from the point of view of the observer.
2. Absolute Magnitude (M) measures the brightness of a stellar object from 10 parsecs, or a planetary object from 1 Astronomical unit.

### Points of Reference

Some points of reference:

• Sol from Terra: -26.73
• Projects enough light to cast shadows: -5
• Faintest objects observable during the day with naked eye: −3.9
• Faintest stars visible in an urban neighborhood with naked eye: 3
• Faintest stars observable with naked eye under perfect conditions: 6.5
• Faintest objects visible with binoculars: 9.5

### Conversion

Given the absolute magnitude [itex]M\!\,[/itex], for objects within our galaxy you can also calculate the apparent magnitude [itex]m\!\,[/itex] from any distance [itex]D_L\!\,[/itex]:

[itex] m = M + 5 (\log_{10}{D_L} - 1)\!\,[/itex]

One can compute the absolute magnitude [itex]M\!\,[/itex] of an object given its apparent magnitude [itex]m\!\,[/itex] and luminosity distance [itex]D_L\!\,[/itex]:

[itex] M = m - 5 ((\log_{10}{D_L}) - 1)\!\,[/itex]

where [itex]D_L\!\,[/itex] is the star's luminosity distance in parsecs, which are (≈ 3.2616 light-years)

## History & Background (Dossier)

The original magnitude measurement was a scale of 1 to 6 to categorize the stars visible in the Terran skies. This was later formalized into a logarithmic scale, with the smaller numbers indicating brighter objects than larger ones. The scale is defined such that each 5 points magnitude is 100 times brighter (or dimmer). The scale also extends into the negative numbers, so for example magnitude -5 is 100 times brighter than magnitude 0.

## References & Contributors (Sources)

 This page uses content from Wikipedia. The original article was at Absolute_magnitude. The list of authors can be seen in the page history. The text of Wikipedia is available under the Commons Attribution-ShareAlike 3.0 Unported License.
 This page uses content from Wikipedia. The original article was at Apparent_magnitude. The list of authors can be seen in the page history. The text of Wikipedia is available under the Commons Attribution-ShareAlike 3.0 Unported License.
This list of sources was used by the Traveller Wiki Editorial Team and individual contributors to compose this article. Copyrighted material is used under license from Far Future Enterprises or by permission of the author. The page history lists all of the contributions.