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| '''Homeworks 1''' is the attempted solution to our second task<ref>Our first task was to register our PRS, visit the course web-page on Blackboard, look at the textbook, and write an equation for our [[Exercise PhysicsWiki|wiki]]</ref> in the course [[AST4210_5211: Introduction to Astrophysics - Fall 2009|Introduction to Astrophysics]]. This assignment is due on ''Wednesday 09/09/09'' and was assigned on 09/01/09.
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| ==Problem 1==
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| List in order of increasing size and give the approximate size of the following objects: An atom,
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| a biological cell, a cluster of galaxies, the Earth, a galaxy, the Local Group of galaxies, a neutron, a neutron star, a person, the Solar System, our sun. Note: you may have to look in other books besides your textbook to get all this information.
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| # Neutron = <math>3 quarks \; </math> (or <math>r \approx 1 fm = 10^{-25} m \;</math> <ref>Which is larger, the proton or the neutron? http://www.physlink.com/education/AskExperts/ae570.cfm</ref>)
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| # Atom = <math>r \approx 62 - 520 pm = 62 - 520 \times 10^{-12} m\;</math>
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| # Biological Cell
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| # Person
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| # Earth
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| # Sun
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| # Neutron Star
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| # Solar System
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| # Galaxy
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| # Local Group of Galaxies
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| # Cluster of Galaxies
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| ==Problem 2==
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| The nearest star outside the solar system is about 4 light years away.
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| # How far away is the star in kilometers?
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| # Suppose you travel to the nearest star in a rocket ship moving at 100 km per hour (100 km/hr is
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| about 62 mi/hr, a typical automobile speed on a Florida highway). How many years will it take
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| you to get to the star?
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| # Suppose you travel to the star at 10 km per second (the speed of a rocket in orbit around the Earth). How many years will it take you to get to the star?
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| ==Problem 3==
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| Use the size of the Astronomical Unit in kilometers and the length of the year in seconds to calculate how fast the Earth moves in its orbit in kilometers/second.
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| ==Problem 4==
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| Describe the essential differences between the Ptolemaic, Copernican, and Keplerian descriptions
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| of planetary motion.
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| ==Problem 5==
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| Use Newton’s laws to show that the orbits of planets are ellipses.
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| ==Notes==
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| <references/>
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| ==References==
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| * B.W. Carroll & D. A. Ostlie (2007). ''An Introduction to Modern Astrophysics''. Addison Wesley. ISBN 0-8053-0402-9
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