THE SOLAR SYSTEM AND OUTER SPACE
STARS

stars
Photo courtesy of SEDS

by Cory Creed and Lucas Graham

Stars are born in cloud formations called nebula, and live for billions of years as huge glowing balls of hot gas. They begin their lives as clouds of interstellar gases (hydrogen, helium, oxygen, neon, carbon, and nitrogen) and dust. As they grow older, stars become unstable and expand, and, in billions of years, will eventually end their existence in explosions. They expand into giant stars which eventually explode and throw off clouds of gases from their outer layers. When stars explode, clouds of helium and other gases from the original stars are formed which, over millions of years, mix with dust and gases, to make the beginnings of new stars. These materials start to spin faster as gravity pulls them together into balls. More hydrogen gas is pulled into these spinning clouds; the collisions between these hydrogen atoms cause the gases in the clouds to heat up.

Stars are hot and bright because they are huge nuclear reactors. Stars produce great amounts of energy by changing hydrogen into helium through a series of nuclear reactions. This energy source in the center of the stars makes them get hot faster and become brighter. Nuclear fusion reactions begin when the temperature at the core or center of the stars reaches about 15,000,000 degrees Celsius. The energy produced by nuclear fusion heats the gases that surround the centers of the stars, causing them to shine brightly. The largest stars have the shortest lives, as they burn hotter and faster than medium-sized and smaller stars like the Sun, the closest star to the Earth. Stars will continue to glow for millions or even up to 15 billions of years, but most stars are between 1 million and 10 billion years old.

There are more than 200 billion billion stars in the known universe, besides the Sun. Although the Sun is the only star to be close enough to see shaped like a ball, the other billions of stars are so far away that they appear to be no more than tiny dots of light. They are huge balls of glowing gases in the sky. The Sun is only a medium-sized star, but its diameter is more than 100 times the diameter of the Earth. Giant stars have diameters that are about 1.6 billion kilometers, about 1,000 times greater than the Sun's diameter. The smallest stars have diameters of 16 kilometers. The nearest star, besides the Sun, is more than 40 million million kilometers away. The farthest stars are found in galaxies billions of light years away.

Bibliography and Additional Sources of Information

Stars. www. EnchantedLearning.com/subjects/astronomy/

Stars. www.windows.umich.edu/cgi-bin/tour.cgi?link=/the_ universe/Stars.html&sw=false&sn=0&cdp=/windows3.html&cd=false&tour=&fr=f&frp =/windows3.html&edu=mid



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