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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 \;</math> = <math>1.11 \times 10^{-15} m \;</math>) <ref>Which is larger, the proton or the neutron? http://www.physlink.com/education/AskExperts/ae570.cfm</ref> <ref>What are the sizes of protons neutrons and electrons? http://wiki.answers.com/Q/What_are_the_sizes_of_protons_neutrons_and_electrons</ref> <ref>On the Radius of the Neutron, Proton, Electron and the Atomic Nucleus http://www.wbabin.net/physics/yue.pdf</ref>
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| # Atom = empirical atomic radius <math>r \approx 62 - 520 pm \;</math> = <math>62 - 520 \times 10^{-12} m \;</math> <ref>Information about Atomic Radii: http://www.webelements.com/</ref> <ref>J.C. Slater, ''J. Chem. Phys.'' 1964, '''41''', 3199.</ref>
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| # Biological Cell = <math>10 \mu m \;</math> <ref>The Biological Cell on Wikipedia http://en.wikipedia.org/wiki/Cell_(biology)</ref> <ref>Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). [http://www.phschool.com/el_marketing.html Biology: Exploring Life]. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6</ref>
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| # Person = 4'11" = <math>1.4986 m \;</math> <ref>[[User:KimberlyWynne|Kim Wynne]]'s height</ref>
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| # Neutron Star = <math>12 km \;</math> = <math>1.2 \times 10^4 m \;</math> <ref>http://en.wikipedia.org/wiki/Neutron_star</ref> <ref>Paweł Haensel, A Y Potekhin, D G Yakovlev (2007). [http://books.google.com/books?id=iIrj9nfHnesC&printsec=frontcover#PPA12,M1 Neutron Stars]. Springer. ISBN 0387335439. </ref>
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| # Earth = radius of the Earth = <math>6378.1 km \;</math> = <math>6.3781 \times 10^6 m \;</math> <ref>Google "radius of the Earth"<ref>
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| # Sun = radius of the Sun = <math>695500 km \;</math> = <math>6.955 \times 10^8 m \;</math> <ref>Google "radius of the Sun"<ref>
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| # Solar System = radius of the comet Oort Cloud's orbit = <math>7.5 \times 10^{12} km \;</math> = <math>7.5 \times 10^{15} m \;</math> <ref>http://curious.astro.cornell.edu/question.php?number=374</ref>
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| # Galaxy = radius of most galaxies = <math>50000 ly \;</math> = <math>4.73 \times 10^{20} m \;</math> <ref>http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/001205a.html</ref>
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| # Local Group of Galaxies = radius of Local Group = <math>5 \times 10^6 ly \;</math> = <math>4.73 \times 10^{20} m \;</math> <ref>http://www.universetoday.com/guide-to-space/galaxies/local-group/</ref>
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| # Cluster of Galaxies = approximate size of most clusters = <math>5 Mpc \;</math> = <math>1.54 \times 10^{23} m</math> <ref>http://www.damtp.cam.ac.uk/user/gr/public/gal_lss.html</ref>
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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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