On these brisk winter post-Christmas evenings, one has an excellent vantage point from which to see the Andromeda galaxy, the closest galaxy to us from the northern hemisphere.
At a brightness of 3.5 magnitudes, a logarithmic unit of measurement set up by the ancient Greek astronomer Hipparchus to correspond to our eyes' own logarithmic response to light, Andromeda is bright enough to see with the unaided eye.
Andromeda, or Messier 31 (M31), appears as a ‘smudge,’ unlike the distinct twinkling of the stars that appear in projection around it. M31 is 200-300 times brighter than the individual stars that we see, but it is at the same time also very much farther away. So, how does one find it?
If you look tonight, Dec 27, 2015, the Moon will be rising shortly after sunset. In the case that you do look for Andromeda when there is a bit of moon or some light pollution then it will be advantageous to use a pair of binoculars. The best place to look is anywhere that is very dark, and the best time is just after sunet.
M31 is in the constellation of Andromeda. Even so, the best way to see M31 for yourself is to look for an easily recognizable
constellation next to it called Cassiopeia.
Unlike the ancient Greek goddess it is named after, Cassiopeia actually looks like the letter “M” or the letter “W” depending on the vantage point. One half of this letter is more deeply grooved than the other. This more deeply grooved region ‘points’ directly to Andromeda.
Andromeda is notable for being a twin of the Milky Way. This is interesting because it means that if someone were to stand on M31 and look at the Milky Way, our gigantic spiral galaxy which also comprises 200-300 billion stars would look very similar to the 'smudge' that we see through the binoculars.
The Milky Way and M31 are two large spiral galaxies which are the ‘heavyweights’ in the group of galaxies in which they hang out with called the Local Group.
But this seemingly static fixture in the center of your binoculars is anything but motionless. M31 and the Milky Way are on a direction collision course. What will happen when these two mighty galaxies collide is the subject of the next article.