Star Systems and Galaxies

Updated June 2013

1. Most stars are members of groups of two or more stars called star systems. Our star the sun, is not a member of a system.

2. Star systems with two stars in them are called binary systems. Star systems with three stars in them are called triple stars.

3. How can astronomers tell if there is a very dim star in a system? Scientists can detect a wobble in the brighter star due to the effects of the dimmer star’s gravity.

4. Describe eclipsing binary stars: When a dim star passes in front of a brighter star eclipsing it.

5. How can astronomers know if there is a planet orbiting a distant star? They use the same method as the binary star “wobble” method.

6. What is a star cluster? A large grouping of stars.

7. Describe an open cluster: They have a loose disorganized appearance. Contain only a few thousand stars.

8. What is a globular cluster? A large grouping of older stars. Some contain over 1 million stars.

Galaxies9. Galaxy- A huge group of single stars, star systems, clusters, dust, and gas all bound together by gravity.

10. Name the different types of galaxies: Spiral, elliptical, irregular.

11. What is a quasar? Very bright- very far away objects. Probably very active young galaxies.

The expanding universe.12. How do astronomers believe the universe began? The universe formed in an instant, billions of years ago, in an enormous explosion called the big bang.

13. What did Edwin Hubble discover about the universe? The universe is expanding. All galaxies are moving away from each other and away from us.

14. State Hubble’s law: The farther away a galaxy is, the faster it is moving away.

15. Tell me about the cosmic background radiation: It is the leftover thermal radiation from the big bang. It is al around us in every direction. It was discovered in New Jersey!

16. What is dark matter? Cannot be seen directly. We can infer that it is there based on the effects of its gravity. We believe that it is what is holding galaxies together.