By: Bryent Kaneshiro and Dyani Chock Stars By: Bryent Kaneshiro and Dyani Chock

General Information A star is a massive, luminous ball of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. Stars are born when immense clouds of interstellar dust and gas condense through the mutual attraction of gravity.

When the condensed material reaches a critical density, and the material becomes a star. This process is called fusion. The more massive a star, the faster it uses up its fuel for fusion. The most common element in the universe is hydrogen, and this is the primary fuel for fusion in stars. Hydrogen fusion produces helium.

After awhile, the star will begin to exhaust its supply of hydrogen, and will start feeding on the helium. This will produce lithium and heavier elements. In succession, the star will begin to use heavier and heavier elements.

Once the star starts producing iron, it has difficulty making heavier elements. It does produce these elements but in very small quantities. These elements are relatively uncommon in the universe. At this point the star undergoes a variety of changes.

Massive stars will explode in a supernova, sometimes producing a blackhole. Tiny stars will slowly cool and die, becoming cold, dark, dwarf stars.

The lifespan of stars varies from thousands of years for massive stars to billions for smaller stars. Our Sun, which is of average mass, is predicted to live for about 10 billion years. By knowing the distance, mass, magnitude, and chemical composition of a star, we can determine approximately how old it is, when it was born, and when it will die.

Scientists determine how old a star is by looking at its spectra - the data about the chemical composition of the star that is revealed in the frequencies of its light. The more heavy elements present in the star, the older the star. To get a specific age, the mass of the star must also be known.

The amount of light coming from the star can be measured and the more light there is, the bigger the star. However, less light arrives from stars that are further away, so how far away the star is must be taken into account.

Red Dwarf Stars Red Dwarf stars can range in size from a hundred times smaller than the sun, to only a couple of times smaller. Because of their small size these stars burn their fuel very slowly, which allows them to live a very long time. Some red dwarf stars will live trillions of years before they run out of fuel.

Because red dwarf stars only burn a little bit of fuel at a time, they are not very hot compared to other stars. Red dwarf stars are by far the most common type of star in outer space. However very few stars that you see in the sky are red dwarfs. This is because they are so small and make very little light.

Yellow Stars Yellow stars are medium sized stars are yellow because they have a medium temperature. Their higher temperature causes them to burn their fuel faster. This means they will not live as long, only about 10 billion years or so. Near the end of their lives, these medium sized stars swell up becoming very large.

Blue Giants Because blue stars are large, and compact, they burn their fuel quickly, which gives them a very high temperature. These stars often run out of fuel in only 10,000 - 100,000 years. A blue giant is very bright, rare, and they make up many of the stars we see at night. Blue giant stars die in a spectacular way. They grow larger just like the Sun sized stars, but then instead of shrinking and forming a planetary nebula they explode in what is called a super nova.

Video http://www.youtube.com/watch?v=uCz-uXRf4rA

(Super) Giant Stars As a sun sized star gets old, it starts to run out of its hydrogen fuel. When the burning of hydrogen in the star's core begins to slow down, the core gets more compact. This means all the stuff in the middle of the star gets really close together. As the center gets smaller and smaller it starts to heat up again. When it gets hot enough it will start to burn a new fuel called helium.

Works Cited "Star Lifespan: How Long Does a Star Live?" Suite101.com: Online Magazine and Writers' Network. Web. 08 Feb. 2011. <http://www.suite101.com/content/starlifespan-a910>. "Stars." Astronomy For Kids - KidsAstronomy.com. Web. 08 Feb. 2011. <http://www.kidsastronomy.com/stars.htm>. "Stars." Imagine The Universe! Home Page. Web. 08 Feb. 2011. <http://imagine.gsfc.nasa.gov/docs/science/know_l2/stars.html>. "Well Known Stars And Constellations." WWW2 Webserver. Web. 08 Feb. 2011. <http://www2.potsdam.edu/islamma/phys335constellations.htm>.