At the largest scale we know of, the cosmos is composed of hundreds of billions, perhaps as many as a trillion, galaxies. These “island universes” are shaped like eggs in some cases and like flat pinwheels in others. They contain hundreds of billions of stars each. From the standpoint of Earth and its puny inhabitants, they are vast beyond comprehension.
From the standpoint of the whole universe, they are tiny islands of stars lost in the vast cosmic ocean of space. A single telescope field can show scores of very distant galaxies, each one a tiny fuzzy patch.
We live in one of them, of course. The Milky Way is all around us, both as the stars we see with our unaided eyes and the milky stream of light that stretches just after dark from northeast to southwest like the backbone of the night.
The distribution of galaxies in the cosmos is not uniform. Astronomers find clumps of galaxies tied together by loose bonds of gravitation and traveling together like celestial pilgrims. The universe is lumpy.
The Milky Way travels in a small clump called the Local Group, a sparse collection of 30 or so galaxies. It is a poor cluster indeed compared to the richness of more distant groupings. They can contain hundreds, even thousands of galaxies. Their galaxies are sometimes so close together that gravitational wars abound and larger galaxies steal stars from their smaller, weaker compatriots.
The galaxies in the Local Group have some room to move. They are scattered like dust over a three-dimensional void perhaps 5 million light years wide. (One light year is 6 trillion miles. Five million miles is – scientifically speaking and precisely in miles – really, really big.)
The galaxies of our local group vary in size and the number of stars they possess. Two large galaxies, our own Milky Way and the even larger Andromeda Galaxy, dominate the group. Both are spiral galaxies, shaped like children’s pinwheels of perhaps 300 billion stars each.
The other galaxies are smaller spiral galaxies, egg-shaped galaxies called ellipticals, and non-uniformly shaped blobs called irregular galaxies.
The brightest galaxy we see is, of course, the Milky Way. We’re in it and, in fact, part of it, after all. However, we can only see parts of it at a time because it stretches around us in all directions.
If you want to see a whole galaxy all at once, then the Andromeda galaxy is the target of choice, and now is the best time to see it.
As always, you’ll need a star map. Many good ones are available these days for cell phones, and they are remarkably easy to use. Just point your phone in the direction you want to observe, and you’ll see a simulation of what you are actually seeing in the sky.
In that way, point your phone toward the east just after dark toward the constellation Andromeda. Look first toward the southeast and about half way up the sky for the Great Square of the constellation Pegasus. Find the leftmost star of the square and sweep to the second set of two stars. Those stars point upward to the Andromeda galaxy, which is easily visible in binoculars (or to your unaided eye from a dark, rural location).
The cigar-shaped patch of light you see took over two million years to get from the galaxy to your eyeballs. The true glory of this spinning pinwheel of billions of stars is forever beyond your ken. You are not experiencing the galaxy, but its ghost, its dim specter. The rest is separated from you by an unconquerable void of space and time.
Take a look anyway. You are looking at the farthest thing you can see with your unaided eye. You are looking directly into the great nothing and seeing the texture of the universe. In one magnificent and futile effort, you are allowing your reach to exceed your grasp. And that, among all the qualities that define us as a species, is what makes us uniquely and gloriously human.
Programs at Perkins
We have public stargazing sessions at Perkins every Friday night starting at 8 p.m. Some upcoming programs are already sold out. Please call (740) 363-1257 for more information or to reserve tickets.
Tom Burns is director of the Perkins Observatory in Delaware.