ay45c1-page6 - A modern value is 1 AU = 149; 597; 870  1...

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Unformatted text preview: A modern value is 1 AU = 149; 597; 870  1 km : 1.2.3 Newton's Law of Gravitation gives mass of Sun Given the AU, we can use Newton's Law of Gravitation to get the mass of the Sun. This is probably the rst example of true astrophysics: Earth ω F Sun So: GM m R2 = F = m!2R \gravity = centripetal acceleration" M 2 2 3 2 !2R3 = 1yr 3:161yr 7 s (1:50  1013 cm) 10 =G 6:67  10 8 cm3 g 1 s 2 = 2:00  1033 g (a modern value is 1:989  1033 g). 1.2.4 Compare Sun to candle to get its \candlepower" What is the \solar luminosity" L (power or energy per time emitted by )? Use inverse square law for radiant ux, a form of conservation energy: 2 3 1 Candle How to compare to a candle? Not easy before electrical measurements! In modern units, solar illuminance is 127000 lux. 6 ...
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