| Home | Articles | Guide to Observing | Tour of the Constellations | Book Reviews |
A galaxy is a collection of billions or even billions of stars. The nearest galaxy to us is our own – the Milky Way galaxy. Although the Milky Way usually refers to the whitish swath in the sky formed by thousands of dim stars, all the stars surrounding us and our own Sun are part of the Milky Way galaxy. Galaxies are big. Ours has a diameter close to 100,000 light years. Earlier we reduced the Earth to the size of a pea in order to imagine the size of the Solar System. Since the nearest star to our pea-sized Earth was 25,000 miles away, we'll have to reduce things further to cover the entire galaxy.
After shrinking the galaxy for a second time, the nearest star will be an inch away from the Sun. This further reduced galaxy will have a diameter of two miles and the Earth will have vanished to a subatomic dot. The neighboring Andromeda Galaxy will be over 40 miles away in this Tom Thumb universe. And furthermore (and I promise we’re coming to the end of all this), the Andromeda and Milky Way galaxies are merely the largest members of a local group of 17 galaxies which are loosely grouped together.
Since a galaxy is extremely large and also very far way, its distance tends to cancel out its size. The relatively close-by Andromeda Galaxy is the only galaxy seen from the Northern Hemisphere that creates a sizeable image while seen through binoculars. Most galaxies when seen through even a modest-sized telescope tend to be disappointing, particularly after reading about how supposedly large they are. Still, even a small image of a galaxy is not a mere point of light like that coming from a star; galaxies have shapes.
The most typical galaxy shape is the spiral. If you look at a spiral galaxy such as our own – the Milky Way – from "above", it appears to have two arms spiraling out of a central core. It actually looks a bit like a water sprinkler. Each arm consists of millions of stars and the Sun is located on the outer edge of one of these arms. In order to see the central core of the Milky Way galaxy, look towards Sagittarius. We can only see the spirals when looking at a galaxy head-on. When looking at a galaxy edge-on, it appears as a straight line with a bulge around the central core.
To get a better feeling for a galaxy's appearance, look at a coin. If your eyes are directed towards its face, it appears circular. As you let the top edge of the coin fall backwards, it appears elliptical until finally when looking at the coin edge-on; it is a straight line. The galaxies seen from the Earth have all sorts of orientations and appear as circles, ellipses and sometimes straight lines.
While spiral galaxies often appear as ellipses, there are other galaxies whose shapes are inherently elliptical. Unlike the spiral galaxies which posses a delicate-appearing inner structure, the elliptics are simply giant globs of stars. It is difficult to detect their real shapes, as their orientations are unknown.
Because of their small image, galaxies present the ultimate challenge to a skygazer. First, try to determine a galaxy's shape and then look for any sort of internal details. The central core may be a bit brighter than the outskirts. Try to judge how large it is. Look carefully at the galaxy's borders and see how abruptly they terminate. The more you practice, the more you will see.
Examples: M31, M33, M51, M89