Stars

1. Stars

2. How old are they? A 16 24 88 23 56 31 33 24 28 1 49 1 month 4 18 36 26 26

3. How old are they? 1 2 4 5 3 • Lagoon Nebula: Found in Saggetarius (about 5 million years) • Protostar HH-34, Found in Orion Nebula (about 1500 years) • 3. Betelgeuse: super red giant, 8 or more solar mass (6-10 million years) • 4. Our sun: less than 8 solar mass (about 4.5 billion years old) • 5. Crab Nebula: remnant from a supernova (about 1000 years)

4. Star Life Cycle http://www.classzone.com/books/earth_science/terc/content/visualizations/es2807/es2807page01.cfm?chapter_no=visualization

5. Star Properties • Color indicates temperature • Hot stars are blue-white • Cool stars look orange-red • Yellow stars like the sun are medium temperature. • Classifying stars—Hertzsprung and Russell graphed stars by temperature and absolute magnitude in a H-R diagram.

6. Hertzsprung – Russell Diagram • Main Sequence—diagonal band on H-R diagram. • Upper left—hot, blue, bright stars • Lower right—cool, red, dim stars • Middle—average yellow stars like the sun. • Dwarfs and giants—the ten percent of stars that don’t fall in the main sequence

8. White Dwarfs • White dwarf stars can be one thousand times smaller than our Sun, whilst red giant stars can be over one hundred times larger than our Sun. That means that stellar sizes cover a range of (approximately) 1,400 km to 1,400,000,000 km in diameter!

9. The white dwarf stars are circled. They are much smaller than the other Main Sequence stars in the image.

10. Color & Temperature • When glancing up at the night sky, stars all appear to be white in color. In fact if you stop and look more closely, their colors are different. Some stars look redder in color, such as Betelgeuse in the constellation of Orion. These are cooler stars, with surface temperatures of about 2000 K. Others stars appear blue, such as Sirius, the Dog Star. Sirius has a surface temperature of around 15000 K. Our Sun is an average yellow star, with a surface temperature of about 6000 K.

11. Star Composition • Spectroscopes break the visible light from a star into a spectrum • Spectral analysis indicates elements in the stars atmosphere • Spectral analysis gives the temperature, pressure, density, and motion of the stars gases.

12. The Sun • Sun is mostly average: • Middle aged main sequence star • Typical absolute magnitude with yellow light • Unusual - sun is not part of a multiple star system or cluster.

13. The Sun • Fusion of hydrogen occurs in the core releasing huge amounts of energy • Sun’s atmosphere • Photosphere – lowest layer gives off light and is about 6,000 K • Chromosphere –layer about 2,000 km above the photosphere • Corona – extends millions of km into space, 2 million K, releases charged particles as solar wind.

14. Sunspots – dark areas cooler than their surroundings • Increase and decrease in a 10 to 11 year pattern called solar activity cycle • Sunspots are related to intense magnetic fields • Prominences – huge, arching gas columns • Solar flares – violent eruptions near a sunspot • Coronal Mass Ejections (CMEs) – appear as a halo around the sun when emitted in the earths direction. • Highly charged solar wind particles can disrupt radio signals • Near Earth’s polar areas solar wind material can create light called an aurora.

15. Stars • Star magnitude • Absolute magnitude—measure of the amount of light a star actually gives off. • Apparent magnitude—measure of the amount of a stars light received on earth. Why does the sun look so bright even thought it is an average star? Afterall, there are brighter stars out there…