Magnitude

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Magnitude is a unit of measure for the brightness (or visibility) of stellar object. There are two kinds of magnitude, Apparent Magnitude (m) which measures the brightness of a stellar object from the point of view of the observer. Absolute Magnitude (M) measures the brightness of a stellar object from 10 parsecs, or a planetary object from 1 Astronomical unit.

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.

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

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[edit]

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

<math> m = M + 5 (\log_{10}{D_L} - 1)\!\,</math>

One can compute the absolute magnitude <math>M\!\,</math> of an object given its apparent magnitude <math>m\!\,</math> and luminosity distance <math>D_L\!\,</math>:

<math> M = m - 5 ((\log_{10}{D_L}) - 1)\!\,</math>

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

Smallwikipedialogo.png 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.
Smallwikipedialogo.png 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.