b) How many times will the Sun orbit the galaxy in its 10 billion year lifetime?
The nearest "real" galaxy to us is the Andromeda Galaxy, also known
as M 31. This galaxy has an apparent
size of 2 degrees (about four times the size of the full moon!). If
its linear size is 25 kpc, how far away from us is it?
Problem #3:
How long does it take for light from the galaxy in problem #2
to reach us?
Problem #4: The visual magnitude of the bulge of M31 is 4.3.
The spectral type of andromeda is G5, but for the purpose of this excersize
lets assume that it is a G2 like our sun. Using the results of problem
#3 find out the number of stars in the bulge of M31. For simplicity assume
that ALL STARS are like our sun. Hint: Use box 24.1 in your book FETU to
find the absolute magnitude of andromeda (its brightness if it was placed
10 parsecs from us). Compare that with the sun's magnitude, and then use
the table to the left of figure 24.2 which tells the equivalence of magnitude
difference and brightness difference.