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Unformatted text preview: Homework 1 University Astronomy 3/29/10 1 University Astronomy 1017-301 Homework Assignment 1 Instructor: Dr Andrew Robinson Due Date: 9 am Friday, 26 March 2010. To tackle some of the following problems you will need to do some research, using either the textbook or other resources, to find various pieces astronomical data and the values of certain physical constants. For questions requiring calculations, show all important steps. 1. The Solar System is located at a distance of approximately 8.5 kpc (8500 parsecs) from the Galactic Center. How far is this in a. Light-years? b. Astronomical units? c. Kilometres? The Large Magellanic Cloud is 48 kpc away. How long does it take light from this galaxy to reach Earth? 2. Angular distances. a. The Andromeda galaxy has an angular diameter of 190 arcminutes. It is approximately 778 kpc from Earth. What is its linear diameter, in kpc? b. Pluto’s largest moon, Charon, orbits at a distance of 19600 km from the planet. Assuming Pluto itself is 39 AU from the Earth, what is the smallest telescope (give the mirror or lens diameter) that could theoretically resolve the Pluto-Charon system, at visible wavelengths (500 nm). a) there are 3.26 ly/parsec, so distance ≈ 27700 ly b) there are ≈ 206000 AU/pc, so distance ≈ 1.75x10 9 AU c) there are ≈ 3.09x1013 km/pc, so distance ≈ 2.62x10 17 km The LMC is 48000pcx3.26ly/pc ≈ 1.56x10 5 ly away, so it takes 156000 yr for light from this galaxy to reach Earth. a) The small angle formula gives the linear diameter: d = r θ (rad)=r θ (arcsec)/206265 (since 1 rad = 206265 arcsec). Thus, d = 778 kpc x 190 x60/206265 = 43 kpc. Homework 1 University Astronomy 3/29/10 2 3. Solar heating. The average amount of radiant energy from the Sun arriving at the top of Earth’s atmosphere (the Solar Constant) is 1373 W m-2 . Estimate the radiant energy flux falling on a flat 1 m 2 patch of ground located at 43° N latitude at the following times: (a) Noon on the Summer Solstice (b) Noon on the Winter Solstice Notes: assume that the Earth is a perfect sphere and that no absorption of solar radiation occurs in the atmosphere. In general the radiant flux passing through a surface of area A is F sol Acos θ , where F sol is the solar flux arriving at Earth and θ is the angle between the normal to the surface and the incoming rays. Since F sol is given and A=1 m 2 , we simply need to determine θ in each...
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This note was uploaded on 05/11/2010 for the course AST 1017.301 taught by Professor Drandrewrobinson during the Spring '10 term at RIT.
- Spring '10