Magnitude - Term used to describe the brightness of an object. When stars were first measured with a photometer it was found that first magnitude stars were 100 times brighter than sixth, so in the current classification system a difference of 5 magnitudes is taken as representing a factor of 100 in brightness. One magnitude difference then corresponds to a difference in actual brightness of 2.5 times. Objects fainter than sixth magnitude are given increasingly large positive magnitude numbers. Apparent magnitude refers to the brightness with which a star appears in the sky.
Absolute magnitude is used in comparing the total light output of stars.
The absolute magnitude of a star is the apparent magnitude it would have if it were at a distance of 10 parsecs from the Earth instead of its actual distance. The motions of all other objects in the system are dominated by the Sun's gravitational pull and orbit the Sun in one fashion or another. The Sun is only one of about 100 billion stars which make up our galaxy, the Milky Way, and is located on the inner edge of a spiral arm called the Orion Arm at a distance of about 30,000 light years from the galaxy's center. Even though the Sun is moving at a speed of 150 miles per second with relation to the galaxy's center, it takes 225 million years to complete one orbit. The Sun's rotation is not uniform like that of a solid planet, but becomes slower toward the poles.