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Professor Questions Unit 8

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Course / Subject Star , is a heavenly body that generates its own light and other forms of radiation . The mass of a star - that is , the amount of material it contains - can be determined most accurately if the star is a member of a true double , or binary , system at a known distance from the earth and separated from its companion by a measurable distance . The masses of both stars are calculated by measuring their motions over a period of years and applying the mathematical law of gravitation

. Once a star 's diameter and mass are known , its density can be determined . Stars have a relatively small range of masses but a wide range of diameters

Depending on its original mass , the lifetime of a star ranges from several million years to 20 billion years or more . The rate at which hydrogen in a star undergoes nuclear fusion is proportional to the temperature of the star 's core . The most massive stars have the shortest lifetimes , because the more massive a star is , the greater is the temperature of its core . As a star exhausts its store of hydrogen , it usually becomes a giant or super giant the star 's outer layers expand and cool as the core contracts and becomes hotter . The core becomes so hot that helium and heavier elements begin to undergo nuclear fusion . At this stage many stars fluctuate periodically in brightness and are called variable stars . A star of small or average mass...

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