1. Star Systems and Galaxies Chapter 4; Section 4

2. Star Systems and Clusters star systems--members of groups of two or more stars star systems--members of groups of two or more stars

3. Multiple Star Systems Star systems that have two stars are called double stars or binary stars Star systems that have two stars are called double stars or binary stars Those with three stars are called triple stars Those with three stars are called triple stars Often one star in a binary star is much brighter and more massive than the other. Often one star in a binary star is much brighter and more massive than the other. Astronomers can sometimes detect a binary star even if only one of the stars can be seen from Earth. Astronomers can sometimes detect a binary star even if only one of the stars can be seen from Earth.

4. Eclipsing Binary a binary star system in which one star periodically blocks the light from the other a binary star system in which one star periodically blocks the light from the other

5. Star Clusters star cluster —a large grouping of stars star cluster —a large grouping of stars 2 types: 1. open cluster: a star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars

6. 2. globular cluster: a large, round, densely-packed grouping of older stars

7. Galaxies a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity astronomers classify most galaxies into the following types: astronomers classify most galaxies into the following types:spiralellipticalirregular

8. Spiral Galaxy a bulge in the middle---arms that spiral outward---pinwheel pattern a bulge in the middle---arms that spiral outward---pinwheel pattern

9. Elliptical Galaxies a round or flattened ball---contains only old stars a round or flattened ball---contains only old stars

10. Irregular Galaxies does not have a regular shape does not have a regular shape

11. Quasar an enormously bright, distant galaxy with a giant black hole at its center an enormously bright, distant galaxy with a giant black hole at its center look like stars look like stars more than 10 billion light years away more than 10 billion light years away

13. The Milky Way location of our solar system location of our solar system

14. From the side: looks like a narrow disk with a large bulge in the middle From the side: looks like a narrow disk with a large bulge in the middle

15. from the top or bottom: has a spiral, pinwheel shape from the top or bottom: has a spiral, pinwheel shape

16. The Scale of the Universe Universe--all of space and everything in it Universe--all of space and everything in it Since the numbers astronomers use are often very large or very small, they frequently use scientific notation to describe sizes and distances in the universe. Since the numbers astronomers use are often very large or very small, they frequently use scientific notation to describe sizes and distances in the universe.

17. Scientific Notation a mathematical method of writing numbers using powers of ten a mathematical method of writing numbers using powers of ten Each number is written as the product of a number between 1 and 10 and a power of 10. Each number is written as the product of a number between 1 and 10 and a power of 10. For example: 1,200 is written as For example: 1,200 is written as 1.2 × 10 3 (decimal point will be moved three places to the RIGHT) 1.2 × 10 3 (decimal point will be moved three places to the RIGHT)

18. Positive exponent indicates that the number will become larger –you move the decimal point to the right Positive exponent indicates that the number will become larger –you move the decimal point to the right Negative exponent indicates that the number will become smaller—you move the decimal point to the LEFT Negative exponent indicates that the number will become smaller—you move the decimal point to the LEFT

19. One light-year is about 9,500,000,000,000,000 meters One light-year is about 9,500,000,000,000,000 meters in scientific notation, this number is written as 9.5 × 10 15 meters in scientific notation, this number is written as 9.5 × 10 15 meters

20. The bright star Deneb is about 3,230 light- years from Earth. To express this number in scientific notation, first insert a decimal point in the original number so that you have a number between one and ten. In this case, the number is 3.23 The bright star Deneb is about 3,230 light- years from Earth. To express this number in scientific notation, first insert a decimal point in the original number so that you have a number between one and ten. In this case, the number is 3.23 To determine the power of 10, count the number of places that the decimal point moved. Here the decimal point moved three places. 3,230 light-years = To determine the power of 10, count the number of places that the decimal point moved. Here the decimal point moved three places. 3,230 light-years = 3.23 × 10 3 light-years 3.23 × 10 3 light-years

21. Practice Problem: The sun takes about 220,000,000 years to revolve once around the center of the galaxy. The sun takes about 220,000,000 years to revolve once around the center of the galaxy. Express this length of time in scientific notation.

22. Answer: 2.2 × 10 8 years 2.2 × 10 8 years You can then move the decimal point 8 places to the right to get 220,000,000.

23. More Practice Problems: 1.) 61,500 Answer: 6.15 × 10 4 Answer: 6.15 × 10 4 2.) 64,960,000 Answer: 6.496 × 10 7 Answer: 6.496 × 10 7

24. 3.) 0.0000078 Answer: 7.8 × 10 -6 Answer: 7.8 × 10 -6 4.) 0.0000568 Answer: 5.68 × 10 -5 Answer: 5.68 × 10 -5