Observing Project 9C How to Discover Your very own Comet

Few if anybody outside his or her own local observing circles knew of Alan Hale prior to 1995. Some might have thought that at the mention of the name that you were talking about the deceased actor who portrayed the "Skipper" on Gilligan's Island (I made that mistake). The same would be true for names like Thomas Bopp or Yuji Hyakutake. They became famous for the bright comets they discovered that would forever carry their names. How did they do it?

Persistence is one key tool you must possess. Yuji Hyakutake scanned the skies for more than twenty years before finding his very first comet. He then found two in less than twelve months, the second being one of the most spectacular of the twentieth century. Others like Karou Ikeya find comets in droves. In his mid and late twenties he became famous in Japan after finding five of them, the last of which was the famous sungrazer, Comet Ikeya-Seki, which he found at age 31. Ikeya built a business around his fame, designing and manufacturing high-quality telescope mirrors. Ikeya never stopped searching for comets, but had to wait thirty-seven years before finding his next one, Comet 2002 C1 Ikeya-Zhang29. Ikeya-Zhang eventually became a modest naked-eye comet. Other dedicated amateurs like Carolyn Shoemaker (wife of the famed geologist) and William Bradfield have discovered many comets. Bradfield, who is a seventy-seven year old retired rocket scientist working for the Australian government, has bagged eighteen comets since his first find thirty-three years ago. His 2004 comet though was his first after an eight-year slump.

Bradfield does have the advantage of searching the southern hemisphere. Most bright comets that venture close to the Sun seem to come from one of five fami-lies,which are named for the astronomers who have identified them. All five groups have orbits that bring them close to the Sun from well south of the ecliptic plane. Comet Ikeya-Seki was a member of the Kreutz group, a series of comets which all move in nearly identical orbits. All members of this group are likely derived from one parent body. In the case of the Kreutz group, the progenitor is a brilliant comet, which passed within some 500,000 miles of the Sun in the year 372 BC and was observed to split in half. The great comet of 1882 and Ikeya-Seki were both comets of this group as were some 85% of all the comets discovered by SOHO. Most Kreutz comets do not survive their passage within less than 500,000 miles of the Sun's surface but those that do like the Comet of 1882 and Ikeya-Seki went on to become legend. Southern hemisphere observers have the advantage of being able to view Kreutz group sungrazers first as well as those from the Kracht I and Kracht II groups, the Marsden group and the Meyer group.

Pick what you believe is a likely patch of sky, say about 1-3 square degrees and regularly image that patch of space. Like with our asteroid search projects, get to know this little area of space like it was the back of your hand. When something unusual passes through it, it should immediately grab your attention. When comets are close to Earth, nearing the perihelion of a highly elliptical orbit they pick up an enormous amount of speed and thus will leave long streaks on film if left exposed. In fact, in order to get a clear exposure of a comet, it is necessary to track on the comet because it is moving so rapidly in its orbit. So clean exposures of comets taken through a telescope usually show star trails.

So if you want to discover a comet, remember the fundamentals. Be patient and persistent, know your target area of the sky very well and search areas that seem more favorable for cometary discoveries. A disproportionate share of comets are discovered in locations south of the ecliptic. Don't be discouraged if you go weeks, months or even years without finding anything. The greatest comet hunters in our science go many years between finds, but the one thing they have in common is that they never quit. Yuji Hyakutake searched the heavens in a fruitless hunt for comets until he was an old man, but never gave up on his dream. His two decades of persistence paid off with greater rewards than he ever could have dreamed and

29 Ikeya-Zhang is now known to be a short-period comet, orbiting the Sun in just under 200 years and so has been given the designation Comet 153P/Ikeya-Zhang.

now one of the most beautiful comets in history bears his name. Even the greatest of the comet seekers sometimes go many years and even decades between making discoveries, such as Japan's Karou Ikeya. Maybe someday your persistence will pay off too.

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