Earth Science

Beyond the Solar System

Milky Way

Study Tip
The Milky Way Galaxy looks different from other galaxies we have observed because we are viewing the Milky Way from within.

The Milky Way

  • The Milky Way Galaxy is a normal spiral galaxy with around 100 to 400 billion stars.  
  • Each spiral galaxy consists of a disk, a central bulge, and a bunch of spiral arms.  
  • There is a supermassive black hole in the center of the Milky Way Galaxy.
  • We know that our galaxy is a spiral galaxy because the velocities of the stars and gases in the galaxy have a rotational motion.
Study Tip
The Milky Way Galaxy looks different from other galaxies we have observed because we are viewing the Milky Way from within.

Statistics of Our Galaxy

  • Our galaxy’s disk has a diameter of 100,000 light years, and is 3,000 light years thick.
  • The central bulge is about 12,000 to 16,000 light-years wide, and around 6,000 to 10,000 light-years thick.
  • Earth is about 26,000 light years away from the center of the galaxy, and it is a little more than half the way from the center to the edge.
  • The solar system orbits through the Milky Way Galaxy, and a typical orbit takes around 250 million years to complete!
Milky Way
The Milky Way is a spiral galaxy, as shown by this picture from a space telescope.
Concept Check
  • What is the Milky Way? How do we know it spirals?
  • What is Earth’s approximate location in the Milky Way galaxy?