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

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
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 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…