Of my three preferred methods of planning an observing session, I will discuss them in order of simplicity, beginning with the easiest to plan. This first method does not even require a star atlas, if you know the whereabouts of a few good objects with which to begin. The session virtually plans itself. The method works well beginning on any bright object, whether it be a Messier showpiece or simply a bright star. If you have access to a good star chart, then the method can be used on just about any object or star. I now use Uranometria Star Atlas exclusively (2nd Ed.), and own the massive two-in-one volume. For the sake of having to start somewhere, I am going to pick an open cluster in Monoceros, but again, you could pick anything you like.
NGC oc 2232 is bright and not a bad object with which to begin or end a night's observing. It is well suited to small telescopes (6" and under) and medium telescopes (8" to 12"). I cannot speak for larger ones, but I suspect it would work just fine, as we are going to mostly use a low power eyepiece anyway. Once 2232 is in the eyepiece, it is time to get the observing eye ready to work. The cluster is a whopping 29`in size, with most of its members at mag. 6 thru 8. Now, unless there are literally hundreds of cluster stars in front of me, I like to begin with a quick count, just to wake up the eye. 2232 is not very rich, and because of the brightness of the members it is easy to count. If you have the atlas open to Map 116 and look at 2232 in the lower left corner, it is easy to determine which stars are within the cluster and which are without. A group of bright stars lie just outside the border, so don`t count them.
 oc 2232 |
| STScI Digitized Sky Survey 30' x 30' |
Once you have had a look around the cluster, the next step begins (I will devote a post dedicated to more fully observing an object at a later date). Star hopping is the tried and true way of hitch-hiking around the galaxy. If you have a "go-to" scope and have never done much star hopping, or haven't done it in a while, you are missing much of the fun of amateur astronomy. Through star hopping I have come across many delightful and undiscovered nooks and crannies, enjoying star chains, doubles, coloured stars, and even vast dark spaces without a single star showing. You will discover sights probably no one has ever noticed or dwelt on before. If I find a particularly fine spot, I mark it in pencil on the atlas so I can return to it, or tell others. Anyway, we are going star hopping from 2232.
First we need to determine direction. Allow a bright star from the cluster to drift out of the field. With a Dob mount, that star just exited west. North is now 90 degrees counter-clockwise. Let`s begin by heading north from 2232. Go far enough so that the cluster is right out of the field of view. Now return to 2232. Go a bit further north now, using the new stars to guide your progress. Travel slowly and be alert for anything interesting. Keep brief notes. If you see something on the edge of your field of vision (a lovely orange star, for example) and veer off in that direction to center it, make certain you can retrace your steps back to 2232 without using your finderscope or "go to" computer. When you have explored the north area for a reasonable distance, try going south. Again, make several forays, extending your distance a bit each time, but always returning to your old friend 2232. Next comes hopping to the east, and then to the west. By now you should have discovered something interesting, perhaps not shown on any atlas.
After switching from an equatorial mount that I used from 1978 until quite recently, to a Dobsonian mount, I used the above method to relearn and readjust to star hopping. I can now travel quite far from my beginning object and usually find my way back. And now for the advanced version: time to head NW, NE, SW, and SE. This should cover a nice area of sky around your object. How far you go depends on your inner star memory and skill level. You should always discover something of interest, as well as gain confidence using your telescope. You will begin to develop better visual star memory, and perhaps will remember enough to recall certain patterns while lying in bed later that night. You have now gone beyond looking at just "the object" itself and then simply moving on to some other object. I can spend anywhere from 15 minutes searching the field of an object, to over an hour depending on my mood and how much there is to see. If you chose oc 2244 instead of 2232, you will see what I mean, as that is an even richer area.
Planning three or four such objects and related field searches in a night provides a very rewarding and enriching experience. You can plan your objects to keep up with the moving sky, too! In this way you will always have something to see in your ideal sky area. Keep notes of what you saw in each direction, even if there was nothing much unusual.
Next time I will talk about a similar but slightly more advanced type of observing session, using a star atlas to prepare oneself, as well as using a map during the actual session. Hope to see you back here.
Mapman Mike
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