Characteristics of Stars

1. Characteristics of Stars Astronomy Chapter 3.2 Pages 103-109

2. What is a Star? • A star is a sphere of super-hot gases • Mostly Hydrogen and Helium • 1 to 2 percent of a stars mass may consist of heavier elements.

3. The Sun • Our solar system’s star • The Sun is 150 million km away from Earth • Light from the Sun takes 8 minutes to reach Earth

4. The Universe • Billions of galaxies make up the universe • All of space and everything in it make up the universe.

5. Milky Way Galaxy • Massive cluster of stars is called a galaxy • It would take you 25,000 years to travel to the center (250 million billion km) of our galaxy at the speed of light.

6. Andromeda Galaxy • Our neighboring galaxy • Would take 2 million years to reach at the speed of light • This galaxy is visible to the naked eye on a clear night.

7. 4) Helium 2) Nitrogen 3) Hydrogen 1) Oxygen What is the most abundant element in most stars?

8. 4) 25,000 years ago 2) 2 million years ago 3) 300,000 years ago 1) 10 million years ago When did the light that you see actually leave the Andromeda galaxy?

9. Distance to Stars • Earth is about 150 million km from the Sun (93million miles) • That is equal to 1 Astronomical Unit (AU)

10. Distance to Stars • Since Stars are so far away: • A light year is used to express great distances. • Light travels at 300,000 km/s • 1 light year = distance a ray of light travels in 1 year (9.5 trillion km.) • Horsehead Nebula is 1,500 light years away)

11. Proxima Centauri • The next closest star is 40 trillion km from the Sun (more than 260,000AU) • Light takes 4.3 years to reach Earth • Most stars are much further away

12. Distance to Stars • Stars appear to be the same distance from Earth in the night sky • How do we know that they are not?

13. Parallax • Parallax: the apparent change in position of an object when you look at it from different positions.

14. Distance to Stars • Only works for nearby stars(less than 1,000 light years away) • Astronomers look at the star when Earth is on one side of the sun and again six months later.

15. Distance to Stars • They measure how much the star appears to move against the background of stars • The less the star appears to move the further away it is.

16. Distance to Stars

17. 4) 25,000 m/s 2) 2 million m/s 3) 300,000km/s 1) 10 km/s What is the speed of light?

18. Characteristics

19. Classifying Stars • Size (Mass) • Color & Temperature • Brightness

20. Mass (size) • Mass is the total amount of material in a body • How much “stuff” or matter something contains • Some stars are five, ten or more times the size of our Sun. Others are less massive.

21. Types of Stars Medium Size Star - Our Sun

22. Types of Stars Giant Stars – are 10 to 100 times larger, having no more Hydrogen • Rigel

23. Types of Stars Super Giant – 10 to 70 times more massive • V838 Monocerotis

24. Types of Stars White Dwarf- about the size of Earth, but with the mass of the Sun

25. Types of Stars Neutron Star – stars that are super small, super massive, and have become pure neutrons

26. 4) Density 2) Gases present 3) Color 1) Temperature If a star can differ in volume (size)and mass, what else will differ as a result?

27. Density of a Star • One teaspoon full of material from Sirius (White Dwarf) is so dense that on Earth it would weigh a ton.

28. 4) Blue 2) Orange 3) Yellow 1) Red What color would you expect a cool star to glow?

29. 3) Yellow 2) Orange 4) Blue 1) Red What color would you expect a hot star to glow?

30. Temperature • How can the temperature of a star be determined? • By the color • Red Stars = Cool • Blue Stars= Hot

31. 4) 50,000˚C 2) 5,500˚C 3) 10,000˚C 1) 3,900˚C The Sun is a yellow star, what temperature would you expect the sun to be close to?

32. Temperatures & Colors 1. Red Stars ~ 3,000◦C (Betelgeuse) 2. Red-Orange Stars ~ 5,000 ◦C (Aldebaran) 3. Yellow Stars ~ 5,500◦C – 6,000 ◦C (Sun) 4. White Stars ~ 10,000◦C (Sirius) • Blue Stars ~ more than 15,000◦C (Rigel)

33. Brightness (Luminosity) • Stars are far from Earth • As a result, what problem does this cause? • Cannot accurately determine the actual brightness of a star from earth • How bright a star appears from Earth depends on far away the star is.

34. Brightness (Luminosity) • Brightness depends on size and temperature • Betelgeuse is large but cool. Its size makes it appear bright • Rigel is smaller but is very hot so it shines brightly.

35. Apparent Magnitude • The measure of how bright a star appears to be from earth. • Less bright objects that are closer to you could be seem brighter than objects that are far and actually brighter • The lower the magnitude the brighter the star.

36. Absolute Magnitude • The brightness of a star if it was set at a standard distance from Earth. • Astronomers calculate the star’s apparent magnitude and its distance from Earth. • Then calculate the brightness if it were a standard distance from Earth.

37. 1) How bright a star appears to be 2) Brightness of a star at a set distance 4) Size and temperature of a star 3) Temperature of a star Absolute Magnitude determines…

38. HR- Diagram

39. HR-Diagram • Herzsprung and Russell • A graph used to find out if temperature and brightness are related. • Plots Absolute Magnitude vs. Surface Temperature.

40. HR- Diagram • More than 90% of stars are Main Sequence, form a diagonal band.

41. What to Work On • Read Section 3.2, pages 103-109 • Answer the section review questions on page 109 (#’s 1-4) DUE: Friday, April 13th