1. Chapter 15 Section 4 Star System and Galaxies

2. Star Systems and Cluster Most stars are members of two or more star systems; Multiple Star System, Star systems that have two stars are called binary stars. Eclipsing Binaries, is the system in which one star periodically blocks the light from another. Star Clusters: –Open clusters contain few thousand bright stars. –Globular Clusters contain more than a million old stars densely packed.

3. Galaxies A galaxy is a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity. Quasars are active young galaxies with giant black holes at their center.

4. Types of Galaxies 1. Spiral Galaxies have a bulge in the middle and Arms that spiral outward. Our solar system is located in a spiral galaxy called the Milky way. 2. Elliptical Galaxies are round, like balls, or oval, like eggs, most elliptical galaxies contain old stars. 3. Irregular galaxies have no regular shape, in general they have many bright young stars and lots of gas and dust.

5. The Scale of the Universe Universe is everything in space and it is enormous, beyond imagination. Astronomers frequently use scientific notation to describe size and distance in the universe.