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# HW3 - ASTR302 Homework#3(due in class on Monday 1 Assume...

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ASTR302 Homework #3 (due in class on Monday, February 18, 2008) 1) Assume that the Sun’s current luminosity (3.86 x 10 26 W) has remained constant over the last 4.5 billion years. Also, the current mass of the sun is 1.99 x10 30 kg. a) Estimate how many kilograms of hydrogen the Sun has consumed over the past 4.6 billion years. b) Estimate the amount of mass that the Sun has lost as a result. c) What percentage of original mass has the sun lost over its lifetime? d) In fact, the Sun’s luminosity when it first formed was only about 70% of its present value. With this in mind, explain whether your answers above are an overestimate or an underestimate. 2) Sunspots typically consist of two regions: an umbra (T ~ 4300K) surrounded by a penumbra (T ~ 5000K). The surface of the photosphere is ~ 5800K. a) Find the wavelength of maximum emission from the umbra. b) Find the wavelength of maximum emission from the penumbra. c) Find the ratio of the energy flux from a patch of a sunspot’s penumbra to the energy flux from an equally large patch of undisturbed photosphere.
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