E4N3_Nov10[1] - Why is a Star Hot? Independent of the...

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Why is a Star Hot? • Independent of the nature of the energy source, stars radiate because they are hot • We must ask, Why are stars hot? – Because they have an energy source… What is the source of energy ?
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Balancing the Stellar Energy Budget: The Sun’s Case History • Evidence from radioactive dating of the Solar System indicates it is about 4.6 billion years old . This suggests that the Sun must have an energy supply that lasts at least that long. Chemical energy could only fuel it for about 50,000 years . Gravitational energy (if it were slowly contracting) can fuel it much longer: 5 million years —still far short of what we need. What else is there…
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: the Special Theory of Relativity • Originally the most controversial modern theory, it became the best-tested. • It rests on two assumptions : 1) The laws of physics are the same in any uniformly moving (inertial) frame of reference. 2) The speed of light in a vacuum is constant
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E4N3_Nov10[1] - Why is a Star Hot? Independent of the...

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