Astronomy HW3

# Astronomy HW3 - Astronomy 1F03 Problem Set 3 Tuesday, Nov...

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Astronomy 1F03 Problem Set 3 Tuesday, Nov 15th, 2011 Please write your answers on a separate sheet and show your working. 1. Determine the rate at which hydrogen is being converted into helium at the core of the Sun. a) Start with the solar luminosity, 4 × 10 26 Watts, and determine the rate at which mass is being consumed using Einstein’s formula, E = mc 2 . b) Use the fact that a Helium 4 nucleus weighs 6 . 64638 × 10 - 27 kg and a Hydrogen nucleus (a proton) weighs 1 . 67262 × 10 - 27 kg to convert the mass loss rate into a number of reactions per second, 4 H 4 He . 2. Stars spend most of their lives on the main sequence and burn an appreciable fraction of their total hydrogen to helium in this period. In the following assume that stars spend their whole lives on the main sequence burning at a Fxed luminosity and that all stars burn a Fxed fraction of their total mass doing so. The Sun’s lifetime is about 10 billion years. Use this to estimate the lifetime of: a) A 0.2 solar mass, 0.1 solar luminosity red dwarf star.
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## This note was uploaded on 02/11/2012 for the course ASTRONOMY 1f03 taught by Professor Wadsley during the Spring '11 term at McMaster University.

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