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Planetary Motion

  1. Oct 25, 2008 #1
    1. The problem statement, all variables and given/known data
    The sun rotates around the center of the milky way galaxy at a distance of about 30,000 light years (1ly= 9.5*10^15m). if it takes about 200 million years to make one rotation, estimate the mass of our galaxy. Assume that the mass distribution of galaxy is concentrated mostly in a central uniform sphere.

    2. Relevant equations

    G Msun Mgalamy / r^2 = Mgalaxy v^2/ r

    3. The attempt at a solution
    r= (30000 * (9.5 * 10^5) ) m
    v= 2 * pi * r / 200 million years
    i know i have to convert the years into seconds is my setup right?
  2. jcsd
  3. Oct 25, 2008 #2


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    You have the equations slighty wrong. Your's would cancel the mass of the galaxy leaving only the mass of the sun.

    And yes - you should work in m/kg/s
  4. Oct 25, 2008 #3
    i am not sure what equation to use
  5. Oct 25, 2008 #4


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