homework1_wsol - (questions adapted from Astronomy Today,...

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Homework 1 1. Calculate the angular diameter of a prestellar nebula of radius 300 A.U lying 50 pc away from earth. Compare this with the apparent diameter of Andromeda, 6 o . Can be solved in two ways: a. Definition of parsec: The distance for baseline of 1AU, parallatic angle 1''. definiton our problem (radius 300 AU, diameter = 600 AU) By proportionality, the angular diameter must be 12'' = 0.0033 o . b. Using the formula given in your book, or classnotes, diameter = distance x angular diameter / 57.3 o . 1 pc = 2.07 x 10 5 AU. 600 AU = 50 x 2.07 x 10 5 AU x angular diameter / 57.3 o . angular diameter = 600 x 57.3 o / (50 x 2.07 x 10 5 ) = 0.0032 o . 2. How close would the nebula in the previous question have to be in order to have the same angular diameter as the Andromeda?
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Unformatted text preview: (questions adapted from Astronomy Today, page 631, problems 1,2) 600 AU = dist (AU) x 6 o / 57.3 o , therefore dist = 5730 AU 1 pc 1 AU 1'' 50 pc 600 AU ? 3. The figure shows the period-luminosity relation, discovered by Henrietta Leavit, for Cepheid variables. a. What is the approximate luminosity of a Cepheid variable whose period is 5 days. (Solar luminosity = 4 x 10 26 Watts) b. The flux observed for this source is 10-15 Watts/m 2 . What is the distance to this object in parsecs? Solution: a. From the graph L ~1000 solar = 4 x 10 29 Watts b. 10-15 Watts/m 2 = 4 x 10 29 Watts / 4 x π x distance 2 . Distance = 5.5 x 10 21 m = 180 kpc...
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This note was uploaded on 11/01/2009 for the course PHYS 229 taught by Professor Mehmetyali during the Fall '09 term at Sabancı University.

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homework1_wsol - (questions adapted from Astronomy Today,...

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