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A submission to the September, 1996 newsletter of an astronomy club I attended at the time.
1996 has proved to be an interesting year for me in amateur observing. I have done a number of activities of personal interest, ranging from seeing Barnard's Star move against its starry backdrop, to attending the third Nebraska Star Party over the summer. There was, however, one particularly noteworthy pair of celestial objects that make this year special -- two bright comets whose show is still not yet over.
As I became more interested in amateur observing as an older child and later as a teenager, I heard many stories about the brilliant comets previous generations had beheld. When Halley's Comet returned in 1985 there were still enough people around who had witnessed its previous passage in 1910 -- compared to which the 1985 passage was a feeble ghost. The names of these brilliant visitors -- West, Ikeya-Seki, Arend-Roland, numerous others -- were all over both popular and technical guides to astronomy.
Yet with a few exceptions (Halley from dark sites in the southern hemisphere, for example) nothing even remotely approaching the quality and brilliance of these comets had graced our skies for over a decade; few had been well-placed for evening observations (the most convenient time for most people) for several decades. As of late 1995, though I had seen several faint comets in telescopes, I had managed to see only three comets that were visually interesting with modest equipment: Halley (1985-86), Levy (1990), and Swift-Tuttle (1992); furthermore, for me only Levy was a naked-eye object. A serious drought was occurring.
Soon, however, the drought would break. In July, 1995, just as the second Nebraska Star Party was enthralling me, veteran comet hunter Alan Hale and amateur observer Thomas Bopp independently noticed a hitherto unknown comet in Sagittarius. Comet Hale-Bopp, named after the first two people to spot it, soon showed itself to have exceptionally high intrinsic brightness -- that is to say, even at a relatively great distance it could be expected to be a very bright object. Still well beyond the orbit of Mars when discovered, Comet Hale-Bopp was tracked, and shown to pass closest to the Earth in early 1997, at which time it could well be a "Great Comet" similar to those mentioned prominently in accounts from decades and centuries past.
Like many amateurs, I sat down, pored over the charts and the ephemerides, and prepared to wait -- the drought was likely ending, but not for another 18 months.
In February, 1996, however, a message on one of the Internet newsgroups caught my eye -- and doubtlessly those of many other amateurs around the world. Japanese comet hunter Yuji Hyakutake had discovered a faint comet, still near the orbit of Mars, which would pass within 10 million miles of the Earth in March. After reading this message, it became clear to me that another major comet was likely to upstage Hale-Bopp, and in amazingly short order.
Since Hyakutake was moving so close to the Earth, it would move and brighten very slowly, until just a week or two before closest approach; as a result, I did not get a chance to hunt it until early March. Early on the morning of March 12, 1996, I was barely able to see it without optical aid from a field near an Urbana high school; in my 70mm binoculars, it was just a faint fuzz. Nonetheless, it was myfirst sighting, and already it had become a naked-eye object. I returned home satisfied.
The following night I drove out of town and got a much better view. In my binoculars, I was able to see a tail, about a degree long. In my trusty Astroscan, ERNI ("Edmund's Rich-Field Newtonian Instrument"), I was able to separate the bright nuclear region from the coma (the large, roughly circular area of gas and dust making the comet's "head"), though the true nucleus was too small to see. Several days later, on the 16th, I was in rural Michigan and able to see 2 degrees of tail with my binoculars, and the comet was becoming an easy naked eye object. It had a magnitude of roughly +3, about as bright as the dimmest stars in the Big Dipper, though it was harder to see because its light was spread out.
The changes in the next week were so dramatic that it is difficult to summarize them. I had already begun to plan a UIAS club outing to see the comet from a dark site in rural Illinois; the comet was living up to expectations and I expected a great show. On March 21, I drove out to my dark site for a "dry run" with my two telescopes, ERNI and BURT (my Big Ugly Red Thing, a Coulter 10" Dobsonian reflector). I found, much to my surprise, a tail nearly thirty degrees long -- the length of the Big Dipper -- and a total magnitude of +0.9, almost as bright as the brightest stars. The tail showed a number of kinks, where gas and plasma had started to break up, and in BURT at 41x there was a prominent jet emerging from the nucleus, causing the center of Hyakutake to look like a "comet in a comet". The outer region of the comet's coma was a pale, yet seemingly quite intense, bluish-green color, very different from terrestrial clouds.
March 22 was the night of the big comet party. With me, I had former UIAS member Suresh Sreenivasan, who had brought a 5" wide-field telescope (the Celestron "Comet Catcher") and an 8" Celestron Schmidt-Cassegrain. Other club members came as well. I had BURT and ERNI, along with my big binoculars, and numerous other people had their own binoculars. Suresh had been mildly incredulous when told of the thirty degree tail the night before, but all doubts were quickly dispelled when the "comet party" began. We were treated to an incredible sight -- a comet with a tail 45 degrees long (one-quarter of the sky) and a total brightness equal to that of the brightest stars visible at the time. In the 8" Celestron at 80x, the "comet within a comet" was prominent, and seemingly white-hot, a different color than the pale greenish-blue of the comet's outer regions. As on previous nights, the comet's pale blue tail had numerous kinks and jets, and the nuclear region showed incredible details in the various telescopes. During this trip, veteran club member Torsten Clay took photographs of the comet.
Yet the best was still to come! Three nights later I went on a private trip, joined by former club member Andrew Martin, to the same site I was at for the "comet party". On the morning of the 26th I was treated to one of the most amazing things I have seen in the sky, exceeded only by the total solar eclipse in Peru in November, 1994. Hyakutake was just transiting -- passing the meridian, at its highest point -- with a tail that pointed almost due south. At this time, the tail was over 60 degrees long, and seemed to bisect the sky neatly. I could understand why the ancients (and, for all I know, many people today) got as disturbed by comets in the past, for all sorts of apocalyptic images could be imagined. The Sword of Damocles? God weighing the world -- indeed, the Universe --in a giant balance? Moreover, the head of the comet was only a few degrees from Polaris, so unlike most celestial objects, Hyakutake did not slide across the sky as the morning progressed, but rather rotated around like a gigantic cosmic searchlight. Hyakutake's impression on the night of the comet party seemed insignificant by comparison.
Later weeks brought the inevitable denouement. Hyakutake was still big and bright the next few days, and even from sites just outside Urbana I was able to make out tail lengths of 20 degrees or more. However, it gradually began to fade. On the night of April 3, I visited a site east of Rantoul that had been recommended by Torsten. Not only was Hyakutake a prominent object, but the Moon was rising in total eclipse! Gradually, the full Moon seemed to shake off its shadow, emerging from the ruddy dull glow of the umbra and reasserting its normal dominance of the night sky. Comet Hyakutake faded under the emerging moonlight, but remained a prominent object in the west, with about 5 degrees of tail in my binoculars. Completing this beautiful tableau was Venus, just west of Hyakutake, nestled against the stars of the Pleiades.
On April 12, 1996, Torsten, Andrew, and club president Megan Jatko joined me at this site to view Comet Hyakutake. Without the Moon around, the visible tail was much longer, still around 30 degrees, but was subtlely changing. The long, kinky gas/plasma tail of March was being modified by dust, becoming yellower and broader. Hyakutake began to fade rather quickly thereafter, as it approached the Sun but receded from the Earth. On April 17th I spotted it, from a dark site east of Urbana, but its tail had shrunk to 5 degrees, and the faint yellow-tan color was prominent. Its brightness had declined to magnitude +2.3 -- still a prominent naked-eye object, but rapidly approaching the Sun. My last view of Hyakutake came on April 20, at a public star party in northern Champaign; between further dimming and urban light pollution, it was below naked eye visibility and was just a faint streak in my trusty binoculars.
Hyakutake rounded the Sun on May 1, and then plunged into the depths of the southern skies, out of reach to those of us in Illinois, fading all the while. I still tracked it indirectly, however, using the World Wide Web and the reports of observers on the sci.astro.amateur newsgroup. As of late August, Hyakutake had faded to magnitude +10, well beyond the visibility of the naked eye or even small binoculars, and for most people was thus just a memory.
Even as Hyakutake speeded away from the inner Solar System, Hale-Bopp began to take the stage. Unlike Hyakutake, Hale-Bopp will pass much further from the Earth, and so will brighten more gradually. I first saw it on July 3, 1996, from the same place I held the Hyakutake comet party in March. At that time, Comet Hale-Bopp was just a fuzz ball, bright but relatively undistinguished in BURT at 55x. On July 10, I saw roughly 10 arcminutes of coma -- still a fairly small object -- and no evidence of a tail. Later in July, I was able to show the comet to my friend Mary Hrovat from a site in Bloomington, Indiana, with the help of ERNI and relatively cooperative weather. It still resembled a small cloud, as yet not visible to the naked eye, though by that time, people in genuinely dark skies were beginning to report its visibility without optical aid.
My first naked eye sighting would have to wait until Nebraska Star Party 3, in August 1996, where the combination of dark skies and dry weather would make for excellent sky transparency. Using ERNI at 16x, I was able -- though barely -- to see a 2 degree tail; with the unaided eye, Hale-Bopp was just a faint fuzzy patch, but one that was moving every day and, with some care, trackable over the course of the week-long star party.
Nevertheless, I have reason for hope. Hale-Bopp is still 7 months from its brightest, and it has already brightened impressively in the last 7 months. At its brightest, it ought to be similar in brightness to Hyakutake near the latter's closest passage to Earth -- which, if true, would make it the second exceptional comet in just over a year. I plan to be out in the dark areas of eastern Illinois, despite the often grim weather of late winter and early spring, to try to recapture some of the thrill I had the previous spring, while still reveling in the unique characteristics of every bright comet, and with any luck having further good stories to relate to other sky lovers, past, present, and future.