Disk of the Milky
The major disk of the Milky Way Galaxy is about 80,000 to 100,000 light years in diameter, about 250-300 thousand light years in circumference, and outside the Galactic core, about 1,000 light years in thickness. It is calm of 200 to 400 billion stars. As a guide to the relative physical scale of the Milky Way, if the galaxy were reduced to 130 km in diameter, the solar system would be a mere 2 mm in width. The Galactic Halo enlarges out to 250,000 to 400,000 light years in diameter. As detailed in the Structure section below, new discoveries indicate that the disk extends much farther than previously thought.The Milky Way's absolute magnitude, which cannot be measured directly, is assumed by astronomical convention to be -20.5, although other authors give an absolute magnitude of -21.3.