Stars

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

2. Variables which affect a star’s brightness: ________________ ________________ ________________ _______________:The amount of light received on Earth from a star. ______________:How large and hot a star is in relation to other stars. 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. Stars form in dark, cool clouds called____________. Something happens to make these clouds__________and __________. Orion Nebula B. The Birth of a Star

5. ________ pulls all of the pieces close to the center and squeezes them creating immense pressure. This contraction could last over a __________years. Another view of Orion More Nebulas

6. Protostar Stage • The temperature of this gaseous body continues to rise until it starts emitting_____________, like the burner of a stove. • Stars that are red have the_________surface temperature and the_____________ wavelength light. • The inside of the protostar continues to increase in temperature. When it reaches about_____________degrees Fahrenheit,____________________________________begins and a star is born.

7. Main-Sequence Stage • Stars have an enormous amount of__________inside of them that pushes them out. • ____________ holds this pressure back and keeps the star together. • It is this balance between pressure and gravity that forms a_______________star.

8. Main Sequence Cont. • Different stars______at different rates. • ______________ produce a large amount of short wavelength, high energy______light. These stars_________their fuel very quickly and burn out within a few million years. • A____________like our Sun, burns its’ fuel much________ and lasts about_____billion years. • _______________ that burn_______and produce________wavelength, low energy______light can last for____________________

9. Red Giant Stage • As a star gets_______, the__________fusion slows in the core and moves out toward the outer part of the star. When this happens, the_________core ________, becomes very hot and increases the hydrogen fusion on the outer part of the star. • This makes the star grow 100’s or 1,000’s of times its normal size. • Eventually the giant uses all of its’ Hydrogen and Helium fuel and______under the force of________.

10. There are many ways that a star can die. The way in which this happens depends on the stars’__________. Burnout and Death

11. A) Low Mass Stars • A low mass star never burns the helium in its’ core, so it never becomes a_________. • Low mass stars_______under the force of_______and form____________.

12. B) Medium Mass Stars • Planetary Nebula • Medium mass stars become__________and fuse helium and hydrogen at a fast rate. • Medium mass stars shrink to_______too, but before they do, they eject their outer layer of gas. This is called a____________

13. C) Massive Stars • Massive stars become___________. They are very large when they finish consuming their hydrogen and helium. They collapse with such force that they explode, producing a_____________. • The intensity of a massive star collapsing produces a super-dense star called a___________. Imagine a star 1,000,000 times bigger than our sun becoming a star that is 20 km across. This would be like taking the Earth (8,000 miles across) and squeezing it down to 100 yards across. One pea sized sample of a neutron star weighs over 100 million tons. • In some rare cases, the red supergiant is so massive that when it collapses it produces a____________

14. Black Hole • Neutron Star

15. Black Holes • Black holes should be very hot. Usually hot things glow brightly, like a star. However, the gravity pulling the surface of a black hole toward the center is so strong that not even light can escape from its’ surface, so they completely disappear from sight. • Anything that gets too near to a black hole is swept in by its’ gravity and lost forever.

16. Study of Stars • ­Scientist study stars by using the Hertsprung Russell Diagram. • The HR Diagram compares a stars___________with its’ _________________

17. Hertsprung-Russell Diagram

18. Determining a Star’s Temperature • A star’s temperature can be determined by its ________. • All objects will glow a different color when heated differently • Colors hottest to coolest:_________ _________ ______ _________.

19. Determining a Star’s Composition • Starlight is separated into a spectrum with a _________________ • 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.

20. A star’s spectrum

21. Light-Years • ____________: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

22. 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. The Sun and You

23. Dense inner_____which is the site of hydrogen fusion. ____________:Energy bounces back and forth before escaping. ____________:Cooler layer of gas that is constantly rising and sinking. Layers of the Sun

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

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

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

27. 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

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

29. _____________:Violent eruptions near a sunspot which suddenly brighten and shoot outward at high speed. Prominences and Flares

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