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Homework Help: Calculating the radius of a HII region - worked out but just need you to check!

  1. Jan 9, 2012 #1
    1. The problem statement, all variables and given/known data
    Estimate the radius of a spherical HII region which rests at a distance of 500 pc that subtends an angle of 20' at the observer. [1'=3x10-4 radians]

    2. Relevant equations


    Where D is the distance, L is the angular size and theta is the angle.

    3. The attempt at a solution

    L= 500*20*3*10^-4 = 3pc


    Radius = 1.5 pc
  2. jcsd
  3. Jan 9, 2012 #2
    Yes, as given, and to the likely limits of precision of the inputs. The 500pc distance in particular probably has ±50pc or more. So my instinct to quibble about how many radians in 1' isn't worthwhile :-).
  4. Jan 9, 2012 #3
    Thank you! :-)
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