1. StarsStars

2. A Star…. Heats and lights the planets in a solar system Is a ball of plasma (4 th state of matter consisting of ionized particles) held together by its own gravity Produces energy by nuclear fusion (4H nuclei  1He nucleus, some matter is converted to energy ) –Energy from nuclear fusion is transferred to the earth (and other places) as: 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 186,282 miles per second

4. How we tell what stars are made of Every chemical element has its own unit spectral fingerprint. We can study the chemical composition of an astronomical object, like stars by observing its absorption or emission spectrum. Emission spectrum (top) and absorption spectrum (bottom) of Hydrogen

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 its temperature (T)  Stars are classified by T in order from brightest to dimmest O, B, A, F, G, K, M [Oh Be A Fine Girl, Kiss Me]  Blue = Hottest, brightest  Red = Coolest, dimmest

7. Hertzsprung-Russell Diagram

8. 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 (HR) diagram

9. 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

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

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

12. 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 spent in this phase Begin their lives as clouds of dust and gas in a nebula Gravity may cause the nebula to contract Matter in the gas cloud will condense into a protostar

13. Life Cycle of Stars Life span of a star depends on its size. –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, the star's fuel will begin to run out.

14. Life Cycle of Stars Most will expand into 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

15. Life Cycle of Stars Most average stars will blow away their outer atmospheres to form a planetary nebula (but no planets are made or exist here) 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

16. 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

17. 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

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

19. Video – How stars create elements http://www.youtube.com/watch?v=neMEo8ZrwuI