How to watch for a comet’s fireworks

Guesstimates
The best consensus from comet experts suggest that after the impactor hits and the resultant dust cloud gradually expands, Comet Tempel 1 could perhaps brighten up to magnitude 6. The faintest star that most eyes will see under dark sky conditions is magnitude 6, so there is a chance that Comet Tempel 1 might just become bright enough to glimpse without any optical aid — but that most likely would be the case only for experienced observers in perfect conditions away from all light pollution.

Another uncertainty is just how long any enhanced brightness will last. Comets that break apart into several fragments tend to remain anomalously bright for many weeks, months, even years. On the other hand, local outbursts that occur on a nucleus that remains pretty much intact might last for only several days.

A classic example of this took place in May 1973 when Comet Tuttle-Giacobini-Kresak unexpectedly increased in brightness nearly 10,000-fold over just a week’s time. It then rapidly faded away, only to brighten again suddenly for a couple of days in July 1973.

At best, Comet Tempel 1 might become 15 to 40 times brighter in the hours immediately after the impact; in less than 24 hours it might go from being a dim 10th-magnitude telescopic object to an easy binocular object. It might even become just bright enough to be glimpsed with the unaided eye at a dark-sky site. From northern latitudes, just locate Spica, then scan the region of sky to its left (east) with binoculars. If you see something that looks like a small fuzzy star or diffuse spot of light, you’re probably looking at Comet Tempel 1!

NASA / JPL Artwork shows the Deep Impact spacecraft in the foreground, shooting a copper-sheathed impactor at Comet Tempel 1.

Elizabeth Warner, director of the University of Maryland Observatory, is serving as the liaison to amateur astronomers for the Deep Impact mission. "The coolest thing for me," she notes, "will be to observe the comet over several weeks and then hopefully (weather permitting) see it on July 4 a bit brighter than on the previous nights and know that we made it brighter."

An Amateur Observers’ Program has been established for amateur observers as guide to observing the comet en route to, during and after the July 4 impact. Helpful information is posted at the AOP Web site. The site is set up so that even astronomy neophytes can get out and observe Comet Tempel 1.

(Almost) prophetic words
Nearly four decades ago, in 1967, astronomer Robert S. Richardson (1902-1981) put forward an idea about a possible comet mission which sounds somewhat like Deep Impact. The chief purpose of Richardson’s hypothetical mission was to "stimulate" a comet, causing the expelled cometary material to "become a powerful source of artificially created photon emissions" (making it appear brighter).

But instead of using a projectile, Richardson suggested sending a probe carrying a nuclear weapon that could be detonated on command at the proper time. He also mused on public reaction to a possible bomb-comet experiment:

"Some people think we ought to give it a try. Others are shocked at the idea of blowing up an innocent little comet that never did any harm to anyone. Converting a periodic comet (like Encke) into a mass of bomb plasma seems to them as bad as shooting a faithful old horse and selling it to a glue factory."

On that scale, comparatively speaking, the worst that will happen to Comet Tempel 1 on the Fourth of July is that we’ll give it a black eye.

MORE FROM SPACE

Space Section Front

Cosmic Log: Cassini's closest encounter Space toilet goes on the fritz ... again! NASA to push ahead with Mars Lab launch Space millionaire confident ahead of liftoff Where have all the little Plutos gone? Cosmic Log: The plan to revive Hubble Interactive gallery: 8 great space telescopes High-speed crash makes hot, 'sterile' galaxies Planetarium entangled in politics   See fireworks on the final frontier Space Section Front   Add Space headlines to your news reader: