Galaxies are plentiful, but which is which?

Greetings stargazers. For many amateur astronomers with small telescopes, spring is galaxy season. At any moderately dark site, which includes most of the Four Corners, you can see scores of these faint, fuzzy blotches.

Unfortunately, fuzzy blotches are all that one can typically see without either photographic assistance, or a bigger scope. With practice, however, you can learn to distinguish all the subtle variations in the shapes of these objects.

Galaxies have historically been categorized into three very general groups – elliptical, spiral and irregular. Many people are familiar with the classic spiral galaxy shape – a flat disk that includes a spiral arm structure, and a central bulge. (When they think of the shape of the Milky Way, they are often really thinking of the Andromeda galaxy, our more massive neighbor in the local galaxy group.) The Milky Way actually has more of a bar structure. And it is the one galaxy that you can’t find a good top view portrait of on-line anywhere.

Elliptical galaxies, as the name implies, are elliptical in shape. This other common galaxy type includes galaxies that might be much more massive than spirals. Ellipticals have no active star-forming regions like those found in the arms of the spiral galaxies. They also tend to have older stars and appear yellower in photographs.

All galaxies have at least two things that you won’t get to see. They each have a supermassive black hole at their center. And extending far out beyond the visible region, is a halo of mysterious dark matter.

This month

The constellation Leo is high in the southern sky. Leo (the lion) can be found most easily by looking for the backward question mark, called the sickle, with the bright star Regulus as the dot underneath. If you are familiar with the pointer stars in the Big Dipper – the two stars at the end of the dipper that point toward Polaris – you can use these same two stars, but go in the opposite direction to get to Leo. Algieba, a little higher up in the sickle from Regulus, is a good double star for a small telescope. The two stars in the double are about one magnitude apart in brightness, so can provide a pleasing view.

If you have an available telescope, there are two nice groupings of galaxies to look for. M95, M96 and M105 are set below the lion’s belly. They are all within three degrees of each other, but may not be quite close enough to be in the same field of view. Below the tail of Leo, M66, M65 and NGC 3628 make up the Leo Trio, a much tighter grouping.

Following Leo in a large region to the east, is the Virgo cluster of galaxies. A small telescope can make out scores of these galaxies, but unless you have a very detailed chart, or lots of practice, it is difficult to tell which is which. But even if you can’t tell them apart, it is fun to see something so distant.

hakes_c@fortlewis.edu

Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.

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