Sometimes, the most rewarding observing sessions are brief forays during a break in the clouds. A quirky shift of the wind is all it takes to render the sky completely clear after a day of storms. In a few minutes, the telescope is ready, but the next bank of clouds is already approaching.
What to observe? Orion is rising over the treetops. I swing over to the Great Nebula, admiring its fuzzy tendrils and the Trapezium at its center. My eyes are not yet dark-adapted, but the nebula is bright enough to forgive me. Anyway, I do not have time to trace its full extent, for the clouds are moving in. On impulse, I try for a much fainter target: the Crab Nebula in Taurus. I slowly sweep the scope around the vicinity of the bright star Zeta Tauri. The Crab suddenly pops into view, a soft blur against a field of faint stars. It is shimmering from atmospheric turbulence. On another night, I might let my telescope stabilize in temperature by exposing the optics to the cold air for several minutes longer, but I do not have that luxury now. I zoom up to the Pleiades. The brightest ones, intensely hot and blue stars, tend to obscure the dimmer members of this cluster of hundreds. Even as the first clouds sweep over the field of view, I can see many more than the nine that I usually discern with my naked eye on the darkest clear nights.
My next stop is the farthest from Earth. The Andromeda Galaxy, also known as M31, is high overhead. I pick up the bright inner section and quite a bit of the faint surrounding area. Near the edge of the same field lies a companion to M31. This small, fuzzy spot is M32, an elliptical galaxy. Another elliptical galaxy, fainter but larger than M32, lies on the opposite side of the Andromeda Galaxy. This is known as M110 or NGC 205. It does not have the bright nucleus of M32, and because of this is not as easy to see. On the other hand, M32 is so small that at low magnifications it may be mistaken for just another star. M110 is not likely to be overlooked in this way. The Andromeda Galaxy itself can be appreciated without the aid of a telescope or even binoculars, although these instruments will be helpful. Using a good planisphere or star chart, find the constellation of Andromeda and note when it will be high in the sky. At that time, go out and find the constellation in the night sky. The galaxy's position should be marked on your chart or planisphere. Compare the map with the sky. Under clear, dark skies the galaxy will be visible to the naked eye as a fairly large and oval patch of light. If you do have binoculars, this will make it much easier to find the galaxy.
From this distant object a couple of million light years away, I traveled to somewhere much closer to home, in the realm of the open star clusters. I had seen the Pleiades earlier, but there are many other attractive open star clusters along the Milky Way. Chief among these is the Double Cluster in Perseus, a pair of clusters that are visible to the naked eye and appear in the same low-power telescope field. There seem to be countless stars visible when one looks at these stellar gems. I had to make one more stop, and make it quickly, for the clouds had covered almost all the sky. NGC 457 in Cassiopeia is known as the Owl Cluster. In a small telescope, it certainly looks like a bird with two projecting wings, a triangular tail, and two bright eyes, all made up of stars. As I put away my scope, I thought about all that I had seen in this short time. My count totaled four open clusters, two gaseous nebulae, and three galaxies. It occurred to me that, with a little planning, I could set up a sequential observing session in which I would start out close to home and end up in the outer reaches of the universe. In other words, I would observe the following objects in this order:
- A planet
- A double star
- A gaseous nebula
- An open star cluster
- A globular star cluster
- A galaxy
These objects represent the stepping stones of distance in our universe. Oddly enough, I got to try out this sequence later on the same night.
Mars was the first object on my list, a mere 100 million kilometers from Earth. Its ruddy disk was large and bright, but showed no detail. Not to worry; I had other worlds to visit.
Directly overhead was the double star Gamma Andromedae, lying about 150 light years away. The brighter star is orange, and the fainter one blue. They were close but separate at 36x.
For the gaseous nebula, I chose M78, 1400 light years away. This nebula is in the constellation of Orion, above the belt. Unlike the much brighter Great Nebula to the South, M78 shines by reflecting starlight rather than emitting its own light. M78 was a wispy patch in my telescope, slightly larger and brighter than the Crab Nebula.
An open cluster of the winter sky is M35, 2800 light years away. This cluster is usually visible to the naked eye, and is resolved into a sparkling field of stars in a small telescope.
I knew that the globular cluster would be tough. M2 and M15, the best globulars of the fall sky, had already set. There was only one globular cluster above the horizon, and that was M79. This cluster was low in the southern sky, where the clouds were thickest. With binoculars, I could tell that the sky was quite clear around M79, and I located it without much trouble. Unlike most open clusters, globulars are distinctly round. Also, most "globs" are not resolved into their component stars in small telescopes. This is because of their greater distance from us. M79, at 35,000 light years, appeared as a soft, round glow with a brighter center.
This left me with only a galaxy to find. My natural choice was M33 in the constellation of Triangulum. For northern observers, this galaxy is second in brightness (and fame) only to the Andromeda Galaxy. In spite of this, M33 can be difficult to find in a telescope. The reason is that M33's light is spread over an area greater than that of the Full Moon in the sky. As a result, the surface brightness is quite low and there is little contrast between the galaxy and the sky background. Binoculars make the search easier, since they condense the galaxy's light by applying only slight magnification. A seasoned observer of M33, I used only my telescope. I star-hopped from the third magnitude star Alpha Trianguli and found the galaxy without a hitch. Although faint, its shimmering silver light covered most of the telescope field and was very pretty. This light was very old as well. As I looked through the telescope, I was seeing the galaxy as it was 2.3 million years ago. My tour of the universe had taken me not only out into space but back in time.
You can make the same type of journey. Set up your own itinerary and goals. You will find that this will sharpen your skills in telescope use and object location. Sometimes there will not be an easy member from each class of object in the sky. Be flexible, and do not be discouraged. You may wish to expand the list to include other types of objects. Or, you might select an object from each magnitude class down to the limit of your telescope. It is easy to increase or decrease the difficulty and challenge of such an endeavor. In any case, this is one more way to have the most fun in the shortest time allotted for telescope use.