STARS

1. STARS Page Keeley Where do Stars Go?

2. Learning goal: Explain the physical properties of stars.

3. Think About It When you look at the night time sky, how many stars do you see? Hundreds? Thousands? Millions? • Although there might be too many stars to count, all stars share similar characteristics? Can you come up with four different groups to characterize the stars?

4. How are stars classified? • Stars are classified according to their physical properties. • Color(Temperature) • Size • Distance from the Earth • Brightness – Apparent magnitude - Absolute magnitude

5. Color and Temperature • Color reveals a star’s temperature • Hot stars appear blue (short wavelength) • Cool stars appear red (long wavelength) • Other colors in between like orange, yellow and white

6. Size of Stars (Mass) • Many stars come in pairs called “Binary Stars” • Binary stars rotate around each other • Scientists use this property to calculate mass of stars

7. Brightness of a star Apparent magnitude: How bright a star looks/appears from Earth depends on • Its size • Its temperature • Its distance from Earth Absolute magnitude: how bright a star actually is.

8. Distances of Stars from Earth • Measured in: • Light years • Use Parallax angles (apparent change in position of an object when you look at it from opposite sides of Earth’s orbit). • The nearest stars have a larger parallax angle

9. Apparent and Absolute Star’s Magnitude Lab

10. Star light, Star bright Lab

11. How is a star born? • A star is born when the contracting gas and dust from a nebula become so dense and hot that nuclear fusion starts • Nuclear fusion takes place when hydrogen atoms fuse forming helium. • What is a nebula?

12. What determines how long a star will live? • A star’s lifespan depends on its mass. • Small mass stars live longer because they use their fuel more slowly • Large mass stars live shorter • A young star has more hydrogen • An old star has more helium • When a star begins to run out of hydrogen it becomes a red giant or a supergiant. • When a star runs out of hydrogen it becomes a white dwarf; a neutron star or a blackhole

13. Life Cycle of a Star

14. Life Cycle of a Star Prentice Hall page 710

15. H-R Diagram • A graph that shows relationship between absolute magnitude and temperature of stars. • About 90% of the stars are in the mainsequence stage • Hottest main sequence stars are the brightest and the coolest stars are the dimmest • Red Giants and Super Giants brightness is because of massive size, not temperature. • The Sun is in the main sequence stage

16. H-R diagram

18. Galaxies • A huge group of stars, dust and gas bound together by gravity. What are the main types of galaxies? • Spiral galaxies (Solar System is in a spiral galaxy called The Milky Way) • Elliptical galaxies • Irregular galaxies

19. Constellations • A group of stars that form a picture

20. How can scientists determine whether a star is moving toward or away from the Earth? • They use Doppler shifts • The light from a star that is moving away from Earth appears red (its waves become longer) • The light from a star that is moving towards Earth appears blue (its waves become shorter)

21. The Expanding Universe • Most galaxies have Doppler Shifts towards the red end of the spectrum. This shows that the Earth and the source are moving away from each other. • The red shift of distant galaxies indicate that the universe is expanding.

22. The Big Bang Theory • States that :- • At one time the entire universe was confined to a dense, hot, super massive ball. • Then, about 13.7 billion years ago, a violent explosion occurred, hurling this material in all directions