1. StarsStars

2. Essential Questions What is a celestial body? What is a star? Wat process powers a star? What is a light year? What is the lifecycle of a star/

3. What is a star? The Celestial Bodies that heat and light the planets in a system A star is a ball of plasma held together by its own gravity –Nuclear reactions occur in stars -Fusion (H + H  He) –Energy from the nuclear reactions is released as electromagnetic radiation, also known as light.

4. 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 SPEED of LIGHT is »186,000 miles per second

5. Characteristics of Stars Magnitude (brightness) –A measure of brightness of celestial objects Smaller values represent brighter objects than larger values –Apparent magnitude How bright a star appears to be from Earth –Absolute magnitude (luminosity) How bright a star actually is

6. Characteristics of Stars Temperature & Color –The color of a star indicates the T of the star –Stars are classified by T Decreasing T (bright to dim) O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me ] http://www.seasky.org/cosmic/sky7a01.html

7. Hertzsprung-Russell Diagram http://www.dustbunny.com/afk/stars/lifecycle/hrdiagram.gif

9. 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

10. 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

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

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

13. Life Cycle of Stars 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. Begins the main sequence phase of the star Most of its life is n this phase

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

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

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

17. Life Cycle of Stars If the star is massive enough, the collapse will trigger a violent explosion known as a supernova 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

18. Life Cycle of Stars 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

19. Life Cycle of Stars http://www.seasky.org/cosmic/sky7a01.html Brown Dwarf Not the right stuff to become a star Black Dwarf

20. Stellar Evolution CFA 15 Microsoft Word

21. Online Quiz