If Comet Tempel 1 behaves as predicted, on the evening of July 3, 2005, it should be shining between 9th and 10th magnitude about 3.5 degrees east northeast of Spica: sky map. It could brighten rapidly to 6th, or even 5th magnitude, making it an easy target in binoculars.

How long will it stay bright? A few minutes? Hours, days, or weeks? When Comet Shoemaker-Levy 9 split after being catastrophically disrupted in July 1992, it remained pretty bright for several months, fading considerably about a year after the split. This impact will not be nearly as disruptive, so my guess is that it will continue to brighten for a day or so, then fade over the next several weeks. But since this type of experiment has never been done, we really do not know.

So what should we expect to see or do?

For beginners: The best way to experience this event is to begin observing the comet on the next clear night. You do need a telescope, but even a small 4-inch or 6-inch reflector will do just fine. Some suggestions:

1. Beginning on the next clear night, try to find the comet with your telescope.
2. When you spot it, note its shape and its size. It may look like mere fuzzy smudge against the background sky. Is it an entirely circular fuzzy blob of light, or is it elongated? Does it have a tail?
3. On other nights, finding and observing Tempel 1 will be easier and easier as you get used to it.
4. If you live in the western part of North America, or in the eastern Pacific, you'll enjoy a direct view of the comet at the moment of impact. Write down what you see, and draw a sketch of it.
5. If you live elsewhere, try to follow step 4 the night before impact and the night after it. You'll probably notice a great brightening from one night to the next!
6. If you like, you can submit your observations to the mission's Amateur Observers Program

For advanced observers: To make observations that could be scientifically useful to the mission, you need the following:

1. A good telescope, and aperture of 6 inches or more, on a good motor driven mount.
2. A CCD system that works with the telescope to resolve details as small as two arcseconds per pixel.
3. Take exposures that are fairly short, no more than a minute. Except during the hours around impact, it might help to "co-add" or "stack" several short exposures to get an total exposure of up to 10 minutes. But around impact time, I do not recommend co-adding several short exposures to make a single long exposure in hopes of revealing more detail. While this is normally a good idea, the comet might be changing so rapidly that you need to use the individual exposures. Later, you can try stacking these images, but do submit the originals
4. Calibrate each exposure with appropriate dark frames, bias frames, and flat fields, but save the original, unprocessed images. Do not enhance the images in any way that would affect the information they contain.

For more information, visit www.deepimpact.umd.edu/stsp

Do not feel as though you must submit your observations to anyone but your own observing log. This will be a historic event, and your own record of it will stay in your memory--and in your observing log--for many years to come.