Five Wild Years Reminiscences of the Leonids Experience 1998 – 2002
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Proceedings IMC Bollmannsruh 2003 29 Five wild years Reminiscences of the Leonids experience 1998 – 2002 Daniel Fischer K¨onigswinter, Germany Abstract This is not a scientific review of the surprises, discoveries and sensations the Leonids brought from 1998 to 2002, but a look back by one observer (and science writer) who often witnessed first-hand what went on in the sky — and also how science finally got its grip on the elusive and striking phenomenon of meteor storms. It was a truly an experience with a deep impact (no pun intended) that is not likely to be repeated... I admit it: before about ten years ago I had considered meteor observing, especially with your own eye, as one of the most useless branches of (amateur) astronomy, with no serious data reduction possible and dubious results. This was not true, at least at that time, of course (see Roggemans, 2004), but the progress made by the IMO had not been widely known to the outside world. Not in- terested at all in systematic meteor watching, I was struck by the idea of meteor storms nonetheless: I had read a lot about the fabulous Leonids storm of 1966 and eagerly devoured two big reviews of meteor storms in British journals. Beech et al (1995) had described these rare phenomena as both spectacular and little understood, while Mason (1995) predicted — using a crude model — storms of the Leonids with ZHRs around 5000 in 1998 and 1999. Would it be worth chasing after those possible storms? I was already travelling a lot for astronomy’s sake, both in the quest for eclipses (1983, 1988, 1990, 1991, 1992, 1994, 1995 and so on) and comets (Halley in 1986), but for meteors? Then again, Brad Schaefer, the American astronomer famous for his professional work on astronomy with the naked eye, had told me in 1988 that for him one meteor storm would be “worth ten eclipses”. And I had been going on a moderately extreme expedition for a meteor outburst once before, to France for the Perseids of 1993: when they approached their marvellous peak at dawn with a ZHR of almost 500, there were clusters of several meteors within just one or two seconds, and they caused a fleeting “storm feeling” indeed. To witness that, going on for many minutes, might actually be worth a substantial effort. Eight time zones towards the East, in fact... That was to be the place for the astronomical event of the century? Whole window panes were missing. The single light bulb on the ceiling was dangling freely, all shades long gone. Instead of a light switch there were two pieces of metal carrying the full 220 Volts which you had to bring into contact with your bare hands. And there was no liquid water whatsoever. So this was the famous “Hotel Edelweiss”, the guest quarters of Mongolia’s only professional astronomical observatory Khu- rel Togoot, some 11 km Southeast of the capital Ulaanbaatar. It must have been a state-of-the-art site once — back in the late 1950’s and early 1960’s, that is, when the socialist “brother nations” from the Comecon had donated the buildings and half a dozen telescopes to their poor Far-Eastern partner. (...) It had been evident from the first minute we had arrived here on November 15, 1998, that this was a strange place. We, that was “ALEX’98”, 14 amateur astronomers from all over Germany, led by Jurgen¨ Rendtel, president of the International Meteor Organization (IMO), among us many veteran visual, photographic and video meteor observers. We were to join a similarly big professional Canadian expedition here, which in turn had teamed up with the United States Air Force. Upon our arrival at the place we were immediately shown the way to the bar and the disco — but no one ever bothered to show us even one of the astronomical instruments. 30 Proceedings IMC Bollmannsruh 2003 Figure 1: Bizarre preview of the 1998 Leonids on the CNN website. These were some of the first impressions of the place where we were waiting for the first meteor storm in decades (Fischer, 1998). The Canadians as well as our group (in which I had ended up more or less by accident, after chatting with an IMO member at a conference) and other amateurs who joined in later were mainly interested in the phenomenon as such while the USAF group was part of the first-ever real-time network that would warn satellite operators in case the meteor rate reached dramatic levels. The weather conditions were mostly fine around the critical day, the equipment — both ALEX and USAF were using numerous intensified video cameras but doing visual counting at the same time — was set up around the “Edelweiss”. And so it began (Fischer, 1998): The first night of observations — November 15 to 16 Mongolian Time = the evening of November 15 UTC — lived up to expectations in that hardly any meteors were sighted. This was what everyone had predicted, and actually most also believed that there would not be many meteors the next night. That would be exactly 24 hours before nodal crossing, and the general expectations were that any background activity from older Leonid particles would only start to ramp up 12 hours before the crossing. How wrong the experts could be sometimes... Usually we would go to bed around 8 p.m. to get up again around 2 a.m. when Leo and the radiant would already have risen (the Lion’s head came above the horizon almost exactly at midnight local time, which is 8 hours ahead of UTC). But tonight there was no need for an alarm clock: those observers who had gotten up early made sure no one overslept tonight. Something totally unexpected was going on: we were literally under fire from a hail of large meteoroid particles. There was at least one meteor visible every minute — normally no big deal, but all of them were very bright. Not one was faint. This was a most unusual brightness distribution: normally you have many more fainter than bright ones, and we would have seen the faint ones easily (the limiting magnitude was always better than +6 magnitude). But now they were all brilliant — and some strikingly so. One, for example, had about the brightness of the full moon and exploded right in the zenith: its train (the ionized trail of atmosphere where the particle burnt up) kept on glowing for many minutes, and you could see it being distorted by the winds in the upper atmosphere. At times there would be several meteor trains visible in the sky at the same time — something exceedingly rare, as you normally have only a few significant trains during a whole night. Who cared that it was −30 degrees Celsius or below? With Leo and the radiant climbing higher and higher, the number of meteors per hour climbed, too. This was not simply due to the improving geometrical conditions: the meteor rate was really rising Proceedings IMC Bollmannsruh 2003 31 fast, as the IMO analysis would later show — the peak rate would not be reached until 01h30m UTC = 07h30m Mongolian time. But we were in a good spot nonetheless: a single observer in Mongolia could easily see 100 Leonids, all rather to very bright, in one hour around 6 a.m. on November 17th (22h00m UTC on November 16th). The ZHR at the time was around 200, according to the global analysis. As usual, there would be lulls in activity and then rapid fire from the sky, like 5 meteors within less than half a minute. Now imagine 5 meteors within a second — some optimistic models had thought that possible 24 hours from now. But would it happen after all? The models had been dead wrong about the ramping up of the background particle component we had seen so spectacularly tonight (and that the Europeans were just now starting to experience — if they had clear skies and had bothered to observe one night “early”). There was a distinct possibility now that the whole prediction business was off and that the “real” maximum the next night could be a dud. There was only one way to find out... Figure 2: Another weird headline about the 1998 Leonids and the international expeditions to Mongolia. How it went on is well known now, of course: only a moderate sprinkle of faint meteors was seen from Mongolia or anywhere else during the supposed night of the storm. Numerous guests as well as journalists had come up to the Khurel Togoot Observatory, only to learn — after standing around in the cold for many hours or rather having some drinks, courtesy of the American embassy, that the storm apparently was not coming at all: At 2h20m Mongolian time (18h20m UTC) Col. Worden broke the bad news to the press: “We’re not seeing any increase that would indicate we’ll have a major storm in the next few hours,” he stated and suggested that one might as well go home. “Do you have any idea what happened” someone inquired — Worden: “No!” But let there be no mistake: last night’s “very very strong bright shower of fireballs,” according to Worden, “was probably one of the more impressive fireball shows on record.” For him personally “that’s the most impressive thing I’ve ever seen in the sky.” Even without the storm, the expeditions were clearly a success, and the “Night of the Fireballs” in particular had yielded some of the best persistent train videos ever recorded. The attempt to determine the meteoroid flux in real-time by the Canadians and USAF was also in full swing, with the video signals being scrutinized by both a rudimentary automatic meteor detection system and a human observer, while another observer was doing visual counts directly in the sky.