People have been asking me and many other amateur astronomers if Comet Tempel 1, the Deep Impact mission's destination, is visible through binoculars, telescopes or with the unaided eye. The answer varies, depending on where you are observing and how dark your sky is, but the short answer is no to binoculars and no to unaided eye and yes to telescope visibility in some areas.
Comet Tempel 1 right now is approximately magnitude 10, which is as faint as many of the nearby (in the direction of the comet, that is) galaxies we amateur astronomers look at from dark skies. Magnitude 6 is about as faint as a star as can be seen with unaided eyes from a dark sky, and magnitude 3-5 stars are as faint as we can see from urban locations. Magnitudes are defined in one of the links at the bottom of this announcement.
If you can see, for example, the magnitude 9 and 10 galaxies in Virgo such as M84 and M86 in your telescope then you stand a good chance of seeing the faint comet through a telescope. Here in the LA basin, the sky is too bright and the comet is too faint, but I do plan to give it a try on the 3rd and 4th anyway. I hope you try too. If you can see the planet Jupiter in your sky, then you at least can try to glimpse the comet, and if you can't see it, at least you will know where it is, while you follow the Deep Impact news and images. I collected the material below from the Deep Impact Mission amateur astronomers webpages to help you locate the comet.
Where do I look for the comet?
If you can find Jupiter, the brightest object in the summer sky, then you are in the right neighborhood for locating Comet Tempel 1. This chart, from the Deep Impact website, shows the location of both Jupiter and Comet Tempel 1 on July 3rd at 10:15 p.m. local time from 40 degrees north latitude.
I also like this chart from Sky and Telescope Magazine, which shows the movement of the comet from June 25th to July 10th.
No matter where you live, or what time you try to observe the comet, use Jupiter for your guidepost. If Jupiter is in your evening sky then so is the comet. At the bottom of this email is a list of resources, and the last link - star charts - has lots of charts for different dates and different latitudes around the world. Check them out. And while you're out looking, don't forget to have a last look at Saturn. Last weekend, Saturn made a pretty triangle with Venus and Mercury in the low western sky right at sunset, and the three planets are still visible to the unaided eye. Here's where to look with charts through July 10.
What will Comet Tempel 1 look like?
Tempel 1 is not a very bright comet. At a normal perihelion it typically reaches about magnitude 9. So in the days before the Deep Impact impactor hits Tempel 1, this comet will indeed be a very faint fuzzy diffuse glow visible mainly with telescopes.
After the impact, there are different thoughts as to how bright the comet will become. It's not the brightness from the explosion but rather from the increased amount of gas and dust thrown into the comet's coma by the impact. If lots of dust is released then the comet could get quite bright, possibly as bright as magnitude 5, which is still a faint fuzzy, but bright enough to be seen with binoculars.
Resources on the web
Deep Impact Mission Observers webpage
Definition of magnitudes
Small Telescope Science Program - an observing program for advanced observers, but you can view the images and learn from the pros! http://deepimpact.umd.edu/amateur/advanced/sec4.shtml
Star charts - where is the comet right now?
Upcoming Deep Impact Encounter event list
Last Updated: 24 February 2011