Monday, May 13, 2013

The Moon Over Andromeda

One of my favorite bits of information about the sky is how HUGE the Andromeda Galaxy (M31) is.  The thing about galaxies is that they are terribly dim.  Think about it.   We're inside the Milkly Way galaxy and yet, except for the nearby bright stars, we can barely see it unless we go to the darkest spot we can find.

In fact, the apparent size of Andromeda is serveral times the apparent size of the moon.  This photo where the moon is superimposed shows this clearly.

Even when you do see M31 with the naked eye, which you can from a dark location, it doesn't look this big.  Objects have to be bright to look large.  In the same way, the Pleides is much larger than the moon, but they look tiny on the sky.

Image credit: REU program, N.A.Sharp/NOAO/AURA/NSF