How far can you see without binoculars or telescope, and perceive the shape of what you are looking at? November is a great month for reaching new distances in the night sky.
When looking at distant objects on earth, you are limited by your elevation and how transparent the atmosphere is. Here on the east coast, our relatively low mountain tops limit us to less than 80 miles under ideal conditions — which are rare.
By looking up and out of the atmosphere we can see and resolve the shape of objects much further away. The two most obvious are the moon and sun. The moon is generally about a quarter million miles from the earth, and the sun about 93 million miles.
With the unaided eye, we can easily see other farther solar system objects, like planets, but can’t resolve them as more than just points in the sky. Exceptions to this are rare bright comets. Most comets are a similar distance from the earth as the sun.
As we continue to look further, these distances are going to get much larger, so let’s switch our measurement units to how long it takes light to travel that distance. For the moon, it takes light about 1.3 seconds to get to the earth, for the sun it’s a bit over 8 minutes.
Once we leave the solar system, many more objects come into play. For late fall, in our dark skies of the Wilds region, we can easily see the Double Cluster between Perseus and Cassiopeia. Look for Cassiopeia’s W asterism early in the evening to the east of zenith and look further northeast along the winter Milky Way toward the horizon. These objects should be obvious before you reach the stars of Pereus.
They are resolved by eye into two close smudges of light, separated in distance by roughly the diameter of the moon. Both clusters are about 7,500 light years from us, and each has around 4,000 stars. If you do look at them through a pair of binoculars, they will begin to show their brightest stars among the faint, unresolved light of the fainter ones.
We can go much further yet—still with just our eyes. First let’s look for the Andromeda galaxy. This large elliptically shaped smear of light, between the “W” asterism of Cassiopeia and the nearest corner of the Pegasus square, is about 2.5 million light years from us.
It is a galaxy substantially larger than the Milky Way, comprised of about 400 billion stars. It appears in the sky to be about six times the size of the moon, and easily seen under moderately dark skies. The Andromeda galaxy is well placed in November, almost directly overhead at 9 p.m.
Again, once you’ve found it with your eyes, take another look at it with your binoculars. You may have heard that Andromeda and the Milky Way are predicted to collide in the future. Don’t wait around for this one, as it is expected to happen in about 4 billion years.
But there is one more target that is still further away that you may just be able to see in late fall. You’ll need to be away from artificial lights and with no moon visible. You’ll need to let your eyes fully adapt to the dark conditions—which takes around a half-hour with no screen time.
This is the Triangulum galaxy, also known as the Pinwheel. Start from the Andromeda galaxy and note where Jupiter is—it is the brightest object in the sky and will be in the southeast in the evening. Trace a line from Andromeda toward Jupiter. A bit less than half-way to Jupiter you may note an elliptical patch about twice the size of the moon.
If so, you’ve found the Pinwheel galaxy. This galaxy is roughly 3 million light years away and is composed of about 40 billion stars. It is much fainter and smaller than Andromeda, so be patient in trying to find it. Once you’ve seen the Pinwheel, you can brag that you’ve seen something almost 20 quintillion miles away.