Saturday, November 12, 2011

Observing Galaxies with a 60mm Telescope

This article is part of a series I'm doing on observing with 60mm telescopes. 60mm telescopes are among the most common of first telescopes. My own first telescope was a 60mm which I used for over 10 years, before "moving up" to a 75mm, then over 20 years later to a 200mm telescope. The points in this article are applicable to larger scopes than 60mm, though it is written about 60mm scopes.

In the first article in this series I listed a number of galaxies that can be seen with a 60mm scope. Here I'll cover some of the best, along with tips on how best to observe them with a small telescope.

Conditions for Observing
With a small scope, small things can make a difference between success and failure when observing faint objects. The sky must be right. Low atmospheric moisture levels mean better contrast and more light from the galaxies you want to view. The telescope must be right. It should be in good condition, with clean optics, and most importantly of all, a stable mount that holds the telescope securely on its target, and allows the scope to be moved and pointed easily. The observer should be in a relaxed, unhurried mood.

Bright Galaxies
There are a few galaxies that are bright enough to be seen easily, even with a 60mm telescope. The Andromeda Galaxy, M31, is one of these. In the southern hemisphere the Large and Small Magellanic Clouds are visible to the eye, so they're easy to find and point the scope at. They're also bright enough to show a lot of detail. M31 is too large to fit into the field of view of a normal telescope, but the brightest parts of the halo, the disk part of a spiral galaxy, and the nucleus, the ball of stars at the center of a spiral galaxy, are visible. It is a good observing exercise to see how far from the nucleus of M31 you can go while still being able to tell the halo of M31 from the background sky.

Low powers will give the best contrast in a small telescope like a 60mm. It is more important to be able to make out the galaxy against the background to see it than it is to magnify the detail in them. The higher the level of magnification, the more the light from the galaxy gets spread out, lowering the contrast. The brightest galaxies, like M31, LMC and SMC, M65 and M66 will allow some moderate magnification. Still, they are best viewed at the lowest power possible with the telescope.

If you don't have an eyepiece with a longer focal length than 25mm, you may consider getting one just for observing deep sky objects at low powers with your telescope. either 32mm or 40mm are fairly common. My 40mm eyepiece is my favorite for viewing galaxies, and once it goes into the focuser for the evening, it almost never comes back out.

Dimmer Galaxies
There are many dimmer galaxies visible with a 60mm telescope. Don't expect them to look like the photographs. They'll look like fuzzy gray spots. But they'll have different shapes, brightnesses, and distributions of light across their visible form. Some will have bright centers and dimmer areas around, others will be equally bright all across, others yet will be splotchy or broken into multiple sections.

Near M31 there are two other galaxies, M32 and M110. They are much, much smaller companions of M31, like the LMC and SMC are companions of our galaxy. They are easy to see because they have a high surface brightness. This is the most important determinant for whether a galaxy will be visible in a small scope.

The apparent magnitude is the brightness listed in sky catalogs for galaxies. It's a misleading number, because it is the measure of how much light it would put out if all its light were gathered into one point of light, like a star. But the light is spread out over the whole face of the galaxy.

How much light is put out by any specific part of the galaxy you see is the surface brightness. A galaxy may be bright, but have a low surface brightness. The Triangulum Galaxy, M33, is like this. It is visible in a 60mm scope, but only with difficulty, because any part of it is very dim. Its total light is spread out over a large area of sky. M110 is very bright at any point. It is compact and well defined, making it easy to see compared to M33. So when reading descriptions of galaxies, look for those with a high surface brightness to view with the 60mm scope.

M108 and M109 in the Big Bear both have a high surface brightness. They are spiral galaxies that we see edge-on, so they appear as a short line of light or small lens shape near different parts of the Big Dipper.

M65 and M66 are bright galaxies in the leg of Leo, The Lion, that can be seen together in the same low power field of view. So you can see, and show others, two galaxies at once! There is a third galaxy nearby that's a bit dimmer, but if you can see it, you'll have three galaxies at once.

No comments:

Add to Technorati Favorites