1. Notes- Chapter 4, Section 4: Star Systems and Galaxies Essential QuestionHow do astronomers learn about the structure of the universe? Objectives 1. Explain each type of star system. 2. Describe the major types of galaxies.

2. A. Galaxies- a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity. What is a galaxy?

3. 1. Spiral galaxies- a galaxy with a bulge in the middle and arms that spiral outward in a pinwheel pattern. a. new stars form in the arms Explain a spiral Galaxy. Where do new stars form?

4. 2. Elliptical galaxies- a galaxy shaped like a round or flattened ball. a. contains old stars and have little gas and dust Explain an Elliptical galaxy.

5. 3. Irregular galaxies- a galaxy that does not have a regular shape. a. smaller than other types of galaxies. b. contain many bright, young stars and lots of gas and dust. Explain an Irregular galaxy.

6. 4. quasars- a bright, distant galaxy with a giant black hole at its center. a. enormous amounts of gas revolve around the black hole, the gas heats up and shines brightly. Explain what a Quasar is.

7. Summary

8. B. Star Systems and Clusters- Most stars are members of groups of two or more stars, called star systems. What is a group of two or more stars called?

9. 1. Multiple Star Systems a. Binary stars- star system with two stars. 1. Often one star is much brighter and more massive than the other. 2. Dim companion star revolves around a bright star, the dim star’s gravity causes the bright star to wobble back and forth. Explain how a binary star system works.

10. 2. Eclipsing Binaries- A system in which one star periodically blocks the light from another Explain an eclipsing binary.

11. 3. Star Clusters- Large groupings of stars a. Two types of star clusters 1. Open Clusters- a star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars. 2. Globular Clusters- a large, round, densely-packed grouping of older stars. Explain the two types of star clusters.

12. Open Cluster named “The Pleiades” or Seven Sisters.

14. Summary