# Absolute Magnitude

(Redirected from Absolute magnitude)

Magnitude is a measure of the brightness of a star, planet, or other object in space. The scale is logarithmic and the brighter the object the lower the number.

Magnitude is usually one of two types:

1. Apparent Magnitude (m) and...
2. Absolute Magnitude (M). Absolute Magnitude is the brightness at 10 parsecs distance.

## Description / Specifications

Given the absolute magnitude and the distance to a star, the apparent magnitude can be calculated by: [itex]m = M + 5((\log_{10}D)-1)[/itex] where D is the distance in Parsecs (must be adjusted for extra galactic objects). Thus Antares at M -5.28 as seen from Capital (distance of ~38 parsecs) would be:
[itex]m = -5.28 + 5((\log_{10}38)-1)[/itex]
[itex]m = -5.28 + 5(1.58-1)[/itex]
[itex]m = -5.28 + 5(0.58)[/itex]
[itex]m=-5.28 + 2.9[/itex]
[itex]m=-2.38[/itex]

### Absolute/Apparent Magnitude

Absolute/Apparent Magnitudes for comparison:

Absolute/Apparent Magnitude
Object Absolute Magnitude Apparent Magnitude (Terra) Apparent Magnitude (Capital)
Sun 4.83 −26.73 10.38
Moon (full) n/a −12.6 n/a
Visible during Daylight n/a −3.9 -3.9
Moon (new) n/a –2.5 n/a
Sirius Brightest Star 1.42 −1.47 6.97
Canopus 2nd Brightest star −5.53 -0.7 (-2.04) (0.73)
Vega 5th Brightest star 0.58 0.03 5.96
Antares 16th Brightest star −5.28 1.09 (0.83) -1.35 (-2.38)
Deneb 19th Brightest star −8.73 1.25 (-2.2) 0.96 (-3.09)
LBV 1806-20 −14.2 8.4 8.4
Quasar 3C 273 −26.7 12.8 12.8
• Note the numbers in () above are for adjusted locations of stars on the maps.

## History & Background / Dossier

On ancient Terra the stars of the sky were divided into 6 magnitudes, with 1 being the brightest and 6 the faintest with each division being approximately 2 times difference, this was later revised so that a 1st magnitude star was 100 times brighter than a 6th magnitude star. First Polaris then Vega were taken to be the 0 point on the scale. So each step is the fifth root of 100 different (2.512).

Magnitude is not limited to the 0-6 scale, most primary stars will be highly negative (Sol from Terra is −26.73). The faintest magnitude visible with a human eye is 6.5. Binoculars give 9.5, and an 8m Ground Telescope can resolve to 27.

• Apparent Magnitude: A measure of its brightness as seen by an observer on the ground, normalized to the value it would have in the absence of the atmosphere
• Absolute Magnitude: The apparent magnitude, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction