The Milky Way Galaxy has a length of about 1,000,000,000,000,000,000 kilometers, or 100,000 light years. A light year is the distance that light travels in one year.
The Milky Way galaxy is comprised of an estimated 200 billion stars and potentially 100 billion solar systems, each with planets orbiting similar to those in our solar system. Astronomers detect evidence of other planets by measuring the pull the exert on the stars they orbit. Even though planets are much smaller than stars, they still have a measurable effect on a stars movement.
A super-massive black-hole named Sagittarius A* resides at the center of the Milky Way. It has a mass that is 4 million times greater than that of the sun.