The Milky Way
The Sun orbits about the center of the Milky Way once every 250 to 300 million years. Given an estimated age of our solar system of 4.5 thousand million years, the Sun has made about 15 to 18 orbits of the Milky Way. Our galaxy is an average spiral with a diameter of about 100 000 light years.
Galaxies are classified in a variety of shapes -- elliptical, spiral, barred spiral, and irregular. Astronomers are discovering that many galaxies, including our own, have massive black holes at their centers.
Copyright © 2016 by Bruce Bryson