Stars

1. Stars The Brightness of Stars -Star: A luminous sphere of gas with enormous mass, that produces energy by fusion. -Fusion: The joining of separate nuclei. Common in nature, but not on Earth.

2. Actual vs. Apparent Brightness • 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.

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

4. Lifecycle of Starsvideo: http://www.nationalstemcentre.org.uk/elibrary/resource/5415/the-life-cycle-of-starshttp://www.youtube.com/watch?v=4s7vyDLgk3M http://www.enchantedlearning.com/sgifs/Starlifecycle.GIF

5. Star Lifecycle explained “As space expands there are many more gaps forming and they need to be filled by stars and energy. So stars need to have a dynamic life cycle. Moments of birth and death, right? ” http://library.thinkquest.org/C0110277/stars/life_cycle1.htm

6. Where are stars born? • Nebula (stellar nursery): Stars are born in nebulae-- Huge clouds of dust and gas • Dust and gas particles exert a gravitational force on each other which keeps pulling them closer together. • Orion Nebula

7. More Nebulas • 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

8. Stellar Evolution – A sun-like star http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/sunlike.shtml http://t1.gstatic.com/images?q=tbn:ANd9GcT_XJP25-_6XInCs2WJ2x3ramBhnn-tqYRcDHvFfj96_z1LHKO8kw

9. Huge Stars… http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/huge.shtml

10. Giant Stars… http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/giant.shtml

11. Nothing (even light) can escape the gravity of a BLACK HOLEVideos: http://dsc.discovery.com/tv-shows/other-shows/videos/how-the-universe-works-birth-of-a-black-hole.htm http://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html http://dsc.discovery.com/tv-shows/other-shows/videos/stephen-hawkings-universe-black-hole-time.htm

12. Hertzsprung-Russell Diagram http://aspire.cosmic-ray.org/labs/star_life/hr_diagram.html

13. 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.

14. 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

15. The Sun and You • 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.

16. Layers of the Sun • 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.

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

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

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

20. Cycle of Solar Activity • 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.

21. Solar Flares • Solar Flares: Violent eruptions near a sunspot which suddenly brighten and shoot outward at high speed.

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

23. Earth’s Galaxy—and Others • 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

24. Earth’s Galaxy—and Others • 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

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

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

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

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

29. 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