By Chris Fellows, Serenity Mobile Observatory
Last installment we took a look at Polaris and its surrounding constellations. We also learned a few of the important stars in Cassiopeia and Ursa Major. We are going to build on that knowledge today to identify a third constellation, Andromeda, and find our first deep sky object (DSO), the great Andromeda Galaxy, also known as M31 or the 31st object in the catalog developed by Charles Messier.
First, I would like to set some expectations of what you are going to see through a pair of binoculars or a small telescope. Although planets and some star clusters offer spectacular views with small instruments, most deep sky objects are what we like to call “faint fuzzies.” These objects are fantastically far away and therefor dim. Many of these objects are large in the night sky. The Andromeda Galaxy that we are looking for today is approximately six times the size of the full moon in the sky but is also 2.5 million light years away.
I normally won’t translate light years (a measurement of distance) into miles but let’s indulge just this once so you can get a vague feel for the incredible vastness of the universe. Light travels at 186,000 miles or 300,000,000 meters per second. That is almost unbelievably fast – traveling at that speed you could circle the earth at the equator 7.5 times in one second. If you do the math, the distance light travels in a year works out to be 5,880,000,000,000 (5.88 trillion) miles. The Andromeda galaxy is just over 2.5 million light years from Earth. In other words, its light has been traveling toward Earth for 2.537 million years! So, the distance to Andromeda is 5.88 trillion X 2.537 million = a number of miles so large that if I wrote it out it would take up pages of this article and be completely meaningless. In scientific notation it is written as 1.492 × 10^19 mi – but that is also meaningless to most people. So, I think you can see why astronomers don’t use miles or kilometers as their basic unit of measurement. From now on, we too will use light years (Ly) as our basic unit.
One other thing I would like to mention here that may not be immediately obvious. Since the light, the only information we have about these distant objects, has been traveling to us for, in some cases, millions or even billions of years, we are effectively seeing into the past. When you find the Andromeda Galaxy tonight you won’t be seeing it as it is “right now” but as it was when the light left it 2.5 million years ago. Your telescope is a time machine into the past. Even the moon, our closest celestial object, is 1.4 light seconds away. (That’s the distance light travels in one second, or 186,000 miles.) When you look up you are looking through a window into the past.
OK, that is enough of a tangent from what we set out to accomplish today. Let’s identify a new constellation and a couple new stars, and find the Andromeda Galaxy.
Start off by finding Cassiopeia like we did last week. Remember, it is the big “M” or “W” near Polaris (the North Star). When I look at Cassiopeia I always see it as a “W” no matter what its orientation in the sky. The right side of the “W” is narrower and deeper than the other – look at that side and imagine it as an arrowhead pointing in the direction of the constellation Andromeda. If you can also imagine the depth of that arrowhead as a ruler, then you need to move about 3 arrowheads in the direction it is pointing to spot the Andromeda galaxy.
A second path to M31 is to use the brighter stars in the constellation Andromeda to star hop to it. The constellation Andromeda is connected to the Great square of Pegasus at the bright star Alpheratz and consists of two chains of stars that diverge from that point. The lower chain has two additional important guide stars in it. They are called Mirach, the third star in the chain, and Almach, the fourth and last star in the chain. If you draw a mental line from Mirach through the third star in the upper chain you will be pointing directly at the Andromeda Galaxy.
In exceptionally dark skies the Andromeda Galaxy is a naked-eye object. It looks like a small grayish cloud sitting just outside the Milky Way. You will get a much more satisfying view through a good pair of binoculars or a small telescope. Give it a try the next clear night and let me know if you were able to find it and what your experience was like finding your first DSO.
Chris Fellows, Serenity Mobile Observatory
Find Chris on Facebook (or, if you’re lucky, at your campground). (Editor: Check out his amazing photos on his Facebook page!)