
Practice Finding Angular Size in an Astronomy Context
Shown below is an optical
image of Betelgeuse. Note that
unlike most stars, which appear as point sources, Betelgeuse is big enough
and close enough that the Hubble Space Telescope was able to resolve it. Use the
ruler on the bottom of the image to estimate the physical size of
Betelgeuse, in km. You will need to convert from cm, and it may be easier to
make careful measurements if you first print out the page with the image
of Betelgeuse and the ruler on it. Using the expression for angular
size,
find the angular size of Betelgeuse, in arcseconds. A multiplicative
factor of 6.7 x 10^{9} must be used so that the answer is in
arcseconds (rather than in radians). The distance to Betelgeuse approximatly 130 pc.
