1. StarsStars

2. What is a star? A star is a ball of plasma held together by its own gravity –Nuclear reactions occur in stars (H  He) –Energy from the nuclear reactions is released as electromagnetic radiation

3. Characteristics of Stars DISTANCE –Measured in light-years The distance which a ray of light would travel in one year About 6,000,000,000,000 (6 trillion) miles per year 186,000 miles per second

4. Life Cycle of Stars http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg

5. Life Cycle of Stars 1.Begin their lives as clouds of dust and gas called nebulae Gravity may cause the nebula to contract Matter in the gas cloud will begin to condense into a dense region called a protostar The protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins. 2.Here begins the main sequence phase of the star. Most of its life is in this phase

6. Main Sequence Stars A major grouping of stars that forms a narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell diagram

7. Life Cycle of Stars Life span of a star depends on its size. 3.Very large, massive stars burn their fuel much faster than smaller stars 4. Their main sequence may last only a few hundred thousand years 5.Smaller stars will live on for billions of years because they burn their fuel much more slowly 6.Eventually, the star's fuel will begin to run out.

8. Life Cycle of Stars 7.It will expand into what is known as a red giant 8.Massive stars will become red supergiants 9.This phase will last until the star exhausts its remaining fuel 10.At this point the star will collapse

9. Life Cycle of Stars 11.Most average stars will blow away their outer atmospheres to form a white dwarf 12.Their cores will remain behind and burn as a white dwarf until they cool down 13.What will be left is a dark ball of matter known as a black dwarf

10. Life Cycle of Stars 14.If the star is massive enough, the collapse will trigger a violent explosion known as a supernova 15.If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star

11. Life Cycle of Stars 16.The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons. If the remaining mass of the star is more than about three times that of the Sun, it will collapse so completely that it will literally disappear from the universe. What is left behind is an intense region of gravity called a black hole

12. Life Cycle of Stars http://www.seasky.org/cosmic/sky7a01.html

13. 9.Scientists classify stars according to: _______, _______, & ________ 10. A star’s color reveals its __________. The coolest stars glow ______, while the hottest stars glow ___________. SIZE BLUE RED BrightnessTemperature

14. Types of Stars Classification ClassTemperatureColor O20,000- 60,000 KBlue B10,000 – 30,000 KBlue-white A7,500 – 10,000 KWhite F6,000 – 7,500 KYellow-white G5,000 – 6,000 KYellow K3,500 – 5,000 KOrange M2,000 – 3,500 KRed

15. Q: Based on its color, is our sun very hot? ___________ 11. ___________ of a star depends on its ___________ and __________. Brightness can be measured in terms of _____________or in______________. NO SIZE Temperature Brightness luminositymagnitude

16. 13. _____________ is the measure of light stars generate from their surface. An incredibly bright star has a magnitude of -5 or more, an average star’s magnitude is close to 1, and a dim star’s magnitude is around 10. 12. __________ is how much power the star gives off as compared to our Sun. Our sun’s luminosity is 1. Luminosity Magnitude

17. 14. Each star is born, goes through its life cycle, then ___________. DIES

18. http://www.answers.com/topic/stellar-classification