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Unformatted text preview: Text Quote Notes - Ch. 13 - The Measure of Stars Stars: Distance • the first step is measuring distance, brightness, and lumi- nosity of stars • distances to nearby stars are measured using parallax d ( pc ) = 1 p 00 (1) • 1pc (parsec) = distance of a star with parallax p = 1 00 ( ∼ 3.26ly) • closest star has p=0.75 00 • stars are few and far between in our neighborhood Stars: Luminosity • once distance and brightness are known, we can determine a star’s luminosity • luminosity = 4 πd 2 × brightness • some ? s are 10 10 × more luminous than others • luminosity range of normal stars is from 10- 4 L to 10 6 L • many more low luminosity ? s than high luminosity ones 1 Stars and Radiation: • radiation tells us T, L, R • measuring the color of a ? tells us its surface temperature (Wien) • many more cool ? s than hot ones • many more faint ? s than luminous ones • compare: 2 ? s with same T, different L; which is larger?...
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- Fall '06
- Astronomy, high luminosity ones, Luminosity •once distance