Magnitude and Luminosity
A star is said to have an apparent magnitude, absolute magnitude, and a luminosity.
The luminosity of a star is a measure of how much total energy is radiated from the star per second.
The magnitude of an object can be apparent or absolute.
The apparent magnitude of a star is its brightness as seen from earth. This is measured in relation to other celestial objects. The magnitude of an object can be either negative or positive with lower numbers being brighter. A difference of five magnitudes coresponds to a brightness ratio of 100:1. This means that a star with magnitude 1 is 100 times brighter than a star with magnitude 6. Each magnitude is 2.512 (the fifth root of 100) times brighter than the next higher magnitude. A star of magnitude 1 is 2.512 times brighter than a star of magnitude 2. The brightest star, Sirus has a magnitude of -1.5 while the faintest stars which can be seen by the unaided eye are about 6.
The absolute magnitude of an object is its magnitude at a distance of 10 parsecs away.
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