I. Stars

1. I. Stars • The Brightness of Stars -Star: A hot glowing sphere of gas that produces energy by fusion. -Fusion: The joining of separate nuclei. Common in nature, but not on Earth.

2. Variables which affect a star’s brightness: Star size Distance from Earth Star temperature Apparent Brightness: The amount of light received on Earth from a star. Actual Brightness: How large and hot a star is in relation to other stars. 1. Actual vs. Apparent Brightness

3. Example: (Fig. 20.1) Sirius has a greater apparent brightness then Rigel, even though Rigel is a much hotter and brighter star. Why? Star Brightness

4. Nebula: A large cloud of gas (helium and hydrogen) and dust which forms into a star. Dust and gas particles exert a gravitational force on each other which keeps pulling them closer together. Orion Nebula B. The Origin of Stars

5. As the particles pull closer together the temperature increases. At 10,000,000o C fusion takes place and energy radiates outward through the condensing ball of gas. Another view of Orion More Nebulas

6. Fusion uses up a star’s hydrogen supply rapidly casing the core to heat up and the outer temperature to fall. (Life cycle of the star) Star expands and becomes a red giant Red Giant C. Stellar Evolution

7. Core continues to heat and star expands to a super giant. As the core uses up its helium supply, the outer layers escape into space and the remaining core is white hot and called a white dwarf. White dwarfs Stellar Evolution

8. When no more material is left in the core it explodes into a supernova. Smaller stars become neutron stars and most massive will collapse into a black hole. Neutron Star More Stellar Evolution

9. Nothing (even light) can escape the gravity of a BLACK HOLE

10. Hertsprung-Russell Diagram

11. Determining a Star’s Temperature • A star’s temperature can be determined by its color. • All objects will glow a different color when heated differently • Colors hottest to coolest: Blue/white  yellow  orange  red.

12. E. Hydrogen Fusion: Energy of the Stars • Stars have large amounts of hydrogen gas. • Four hydrogen atoms fuse forming 1 atom of helium • The mass of 4 hydrogen atoms is greater than the mass of 1 helium atom; the excess mass is converted to a tremendous amount of energy.

13. This hydrogen  helium fusion can power a star for billions of years

14. 1. Determining a Star’s Composition • Starlight is separated into a spectrum with a spectrometer • A star’s light has dark bands along the spectrum, these bands are caused by the absorption of certain wavelengths of light by specific gases in the star. • Different bands show what elements are in the star’s atmosphere.

15. A star’s spectrum

16. Pierre Public Schools: F. Light-Years • Light-year: Distance light travels in one year. (Equal to about 9.5 trillion kilometers) • Approximate distances: -Sun to edge of solar system = 5.5 light hours -Nearest star (Alpha Centauri) = 4.3 light years -Center to edge of Milky Way = 50,000 light years

17. Our sun is a main sequence star according to the H-R Diagram. The actual brightness is average for a star of its average size. A. The Sun and You

18. Dense inner core which is the site of hydrogen fusion. Radiation zone: Energy bounces back and forth before escaping. Convections zone: Cooler layer of gas that is constantly rising and sinking. 2. Layers of the Sun (Fig. 20.9)

19. Photosphere: Bright source of much of the light we see. Chromosphere: Active layer which is home to many significant displays. Anatomy of Sun

20. Corona: Outer layer which is a gradual boundary between sun and space. Anatomy of Sun

21. Sunspots: Cool dark areas on the sun’s surface. -First discovered by Galileo -Not permanent features—Will appear and disappear 3. Sunspots

22. Cycle of Solar Activity: 11 year cycle which see number of sunspots change. Sunspot Maximum: Time of many large sunspots. Sunspot Minimum: Time of few sunspots. Cycle of Solar Activity

23. Prominence: A huge arching column of gas. 4. Prominences and Flares

24. Solar Flares: Violent eruptions near a sunspot which suddenly brighten and shoot outward at high speed. 4. Prominences and Flares

25. 4. Prominences and Flares • The interaction of solar flares with Earth’s magnetic field causes the aurora borealis/ aurora australis (Northern/Southern Lights)

26. Galaxy: A large group of stars, gas, and dust held together by gravity. Milky Way: Our galaxy which contains about 200 billion stars and many nebulas Spiral Galaxies A. Earth’s Galaxy—and Others

27. Galaxies are grouped together in clusters. The cluster the Milky Way belongs to is called the Local Group. Three types of galaxies: Cluster of galaxies A. Earth’s Galaxy—and Others

28. Elliptical Galaxies: Most common type of galaxy; large three-dimensional football shaped galaxies. -Contain mostly older and dimmer stars. Elliptical Galaxies

29. Spiral Galaxies: Circular galaxies that have arms curve outward from a central hub. Arms are made up of stars and dust Two spiral galaxies!! Spiral Galaxies

30. Barred spiral galaxies: Have two spiral arms extending out. More Spiral Galaxies

31. Irregular Galaxies: Come in many different shapes and are smaller and less common than elliptical or spiral galaxies. Irregular Galaxies

32. B. The Milky Way Galaxy • 100,000 light years in diameter • Our sun orbits the center of the galaxy once every 240 million years • Probably a barred spiral galaxy • Contains over 200 billion stars • Its where I live!!!!!

33. As waves (sound, light, etc.) move away, the lengths of the waves increases. Doppler Effect C. The Doppler Shift

34. If a star is approaching the dark lines of its spectrum will move toward the blue part of the spectrum. If a star is traveling away (as most are) the lines will move toward the red part of the spectrum. C. The Doppler Shift

35. The conclusion that the universe is expanding because of the red shift in light from galaxies. Quasars: Star like objects at the outskirts of the universe which give off tremendous energy.  C. The Red Shift