How I found a comet
Comet-hunter Don Machholz tells how he found Comet 96P (Machholz) 21 years ago - using homemade binoculars - and how to spy the dirty snowball when it returns this April.
Don Machholz
 Use this sky chart to locate Comet 96P this spring. Astronomy: Roen Kelly [View Larger Image] |
| March 29, 2007
In May 1986, Comet Halley — a naked-eye treat for months — had disappeared from my California sky. Nearly 1 year had passed since I discovered my second comet — 1985e — during the Riverside Telescope Makers Conference in Big Bear, California. On the morning of May 12, my wife Laura and I commuted to my observing site to hunt comets. This session would produce my third — and most exciting — of the 10 comet discoveries I've made. On the hunt After the 40-minute commute to the southern slope of Loma Prieta in the San Francisco Bay Area, I set up my homemade 5-inch (13 cm) binoculars. I built this instrument 3 years earlier from war-surplus aerial-photography lenses and diagonal mirrors. Although the sky seemed brighter than normal, I wasn't going to give up simply because of a mediocre sky. I began sweeping the constellation Cygnus in the eastern sky through the summer Milky Way high in the sky. Over the next 2 hours, I horizontally swept the northeastern sky, through the constellation Pegasus and into its neighbor, Andromeda. "Comet-hunting twilight," when the Sun would reach 15º below the horizon, would arrive about 4:30 A.M. At 3:50 A.M., I swept over M3, M32, and NGC 205. On the next sweep, at 3:52, I picked up an object 2º south of M31 that, at first, appeared to be a close double star. I stopped to give it a longer look and found a fuzzy, condensed object around magnitude 10. I didn't know of any fuzzy objects in this part of the sky, and, as with most of my comet discoveries, immediately thought it might be a new comet. Coincidentally, Phil Collins' "Against all odds" was playing on the radio. A quick check of Antonín Becvár's The Atlas of the Heavens confirmed no nebulous objects exist in this part of the sky. And I didn't know of any comets in the area. I made a drawing of the object, with its location in respect to the background stars, in my log. I thought, "If this is a comet, it should move within 30 minutes." I completed the drawing by 4:03 A.M., and resumed sweeping. About a half-hour later, I returned to the suspect and observed it had moved. It was a comet! |
 Don Machholz poses on his deck with the telescope that helped him bag his tenth comet. Mark Machholz [View Larger Image] My wife and I returned home and I phoned Dan Green, director of the Central Bureau for Astronomical Telegrams at the Smithsonian Astrophysical Observatory. He believed my discovery was a "reasonable suspect." From January 1, 1975, to this May morning, I had spent about 3,616 hours systematically comet-hunting. My first two comets had taken 1,700 hours and 1,742 hours, respectively. This find took an additional 173.5 hours — 1/10th of the average of my first two. The next morning, my wife and my friend Rich Page accompanied me to Loma Prieta. Shortly after 3:00 A.M., I turned my binoculars in search of the assumed comet. I found it, northwest of its previous position, 1.5º away. The suspect was rapidly moving away from the Sun. Upon arriving home, I phoned the Smithsonian again, where word was just coming in from Charles Morris, an expert comet-hunter. Morris and Alan Hale (of Comet Hale-Bopp fame) had observed the comet, too. It was officially confirmed as Comet Machholz, and, being the fifth comet recovered or discovered in 1986, was also termed 1986e. It turned out to be the only comet found visually in 1986. The path less traveled Over the next few weeks, the comet moved farther from the Sun and dimmed. But, during that time, it did not behave in a typical parabolic orbit. By early June, it was confirmed that the comet is in an elliptical orbit, and that it returns to the Sun every 5.24 years. It was then renamed Periodic Comet Machholz. In 1994, when I found my second periodic comet, my 1986 comet became known as Periodic Comet Machholz 1, and, in 1995, with the renaming of comets, it was labeled 96P. The comet gets closer to the Sun than any known periodic comet or asteroid ever found. Because it reaches between magnitude 0 and –2 on each orbit, it is probably the brightest periodic comet, as well. However, at its brightest, it cannot be seen from Earth. It is an annular comet — it can be seen only at its most distant point in its orbit, as far from the Sun as Jupiter. Astronomers are currently debating whether 96P is responsible for any meteor showers. Occasionally, it undergoes outbursts, increasing in brightness by a couple of magnitudes. Apparently, this occurred the day before I discovered it, which is probably why it appeared so sharply defined and small when I found it. Comet Machholz is visible in the SOHO cameras every 5 years, when the comet passes closest to the Sun. In 1996, images of the comet helped calibrate its position. This year, it will be in the SOHO cameras during the first week of April. Prime viewing in 2007 So, with an orbital period of 5.24 years, and having been in this orbit for more than 200 years, why wasn't my comet discovered earlier? Studies show it is bright for only a week or 2 near perihelion. It comes in from the south, whips around the Sun, and shoots back toward the outer solar system. Our Earth-Sun-comet geometry means that for every four passages, three are placed so the comet is difficult to see against the dark sky. However, every four orbits, or 21 years, it makes a passage through the inner solar system similar to when I discovered it in 1986. In 2007, it is placed in our northern morning sky after perihelion, visible in telescopes from mid-April through mid-May. With the Moon out of the morning sky during the last 2 weeks of April, the comet should provide a great view. If you would like to hear me recount this comet, listen to Astronomy.com's podcast . If you observe 96P this spring, be sure to post your observation descriptions or images on Astronomy.com's forum. |
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Don Machholz, the leading visual comet discoverer in the Northern Hemisphere, has found 10 comets visually since he began hunting in 1975. |
