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Leonids 2001

Introduction

With a plethora of peaks of varying strength and duration up to storm level predicted for the 2001 Leonids by different authors, it was always going to be fascinating to see just what happened. In the end, observers in 2/3 of the world enjoyed a superb return of the shower, with two storm-strength maxima visible on November 18. Europe was unfortunately in the unlucky 1/3 of the globe where storm rates were not visible, although this was some relief for British meteor watchers, as here, clouds persisted across the entire country between November 16-17 to 18-19, and scarcely a Leonid was seen! Fortunately, thanks to the splendid efforts by British Section members who had travelled overseas, plus reports from other individuals and groups, this has been our most successful Leonid campaign to date, as this report helps demonstrate.

The Observers

The most important part of any report like this is the contribution made by the many observers and casual witnesses who watched the sky and then reported their results to us. A great debt of gratitude is owed to all the following people for their efforts during the 2001 Leonids. In addition many thanks also go to: Bob Lunsford of the American Meteor Society (AMS) for forwarding extremely extensive data summaries from November 18 in the AMS's journal Meteor Trails No.13 (December 2001; observers whose detailed reports were extracted chiefly from this source are credited below with "AMS". This issue of Meteor Trails also contained an excellent overview of the Leonid storm over the USA, complete with observers' comments); Enrico Stomeo of the Meteor Section of the Unione Astrofili Italiani ("UAI" below) for summaries of their successful Leonid campaign; and Chris Steyaert who provided copies of virtually all the radio data (except that from Dirk Artoos and the Belarus observers, which latter was forwarded to the Section by Rainer Arlt) as Radio Meteor Observation Bulletins (RMOBs) 100-102, November 2001 to January 2002 inclusive (the RMOB website is at: http://www.rmob.org). In the listing, "R" = radio observations, "Vi" = video data and "+ V" = "and visual results". Those not noted provided visual reports.

Enric Fraile Algeciras (Spain; R), Rainer Arlt (South Korea), Dirk Artoos (Belgium; R), Jim Bedient (Hawaii, USA; AMS), Belarus observers (Ivan Bryukhanov, Aleksei Gain, Roman Grabovski, Aleksei Kosinski, Sachar Lapizki, Timur Radyuk, Stanislav Schikun, Vladislav Syrtsev, Valentina Tamello; Belarus; R), Lance Benner (California, USA; AMS), Sushrut Bhanushali (India; AMS), Antonio Blanco (Spain; AMS), Mike Boschat (Canada; R), Brenda Branchett (Florida, USA; AMS), David Branchett (Florida, USA; AMS), Jay Brausch (North Dakota, USA), Matthew Collier (Texas, USA; AMS), Luigi D'Argliano (Italy; UAI), Maurice de Meyere (Belgium; R), Michael Doyle (Virginia, USA; AMS), Gavin D Edwards (Colorado, USA), Andrew Elliott (Arizona, USA: Vi), Steve Evans (Arizona, USA; Vi), Erzsebet Farkas (Hungary; AMS), Didier Favre (France; R), MarLou Gaudet (California, USA; AMS), Joseph Gerver (New Jersey, USA; AMS), Vladimir Getman (Pennsylvania, USA; AMS), Ghent University (Belgium; R), Antonio Gioiosa (Italy; UAI), George Gliba (West Virginia, USA; AMS), W T Goodart (Arizona, USA; AMS), Roberto Gorelli (Italy; UAI), Patrice Guerin (France; R), Rafael Haag (Brazil; R), Walter Haas (New Mexico, USA; AMS), Chaz Hafey (Mississippi, USA; AMS), Roberto Haver (Italy; UAI), Edwin Jones (Arkansas, USA; AMS), Javor Kac (Arizona, USA; AMS), Akos Kereszturi (Hungary; AMS), Yoko Kikuta (Japan), Gene Kispert (Maine, USA; AMS), Girish Kulkarni (India; AMS), Marco Langbroek (Arizona, USA), Trevor Law (Western Australia), Ken Legal (Pennsylvania, USA; AMS), Bob Lunsford (Arizona, USA), Alan MacRobert (Massachussetts, USA; AMS), Pierre Martin (West Virginia, USA; AMS), Felix Martinez (Virginia, USA; AMS), Paul Martsching (Illinois, USA; AMS), Norman McLeod III (Florida, USA; AMS), David Meisel (New York, USA; AMS), Frank Melillo (New York, USA; AMS), Amruta Modani (India; AMS), Sirko Molau (South Korea; AMS), Stan Nelson (New Mexico, USA; R), Gyula Nyerges (Hungary; AMS), Hiroshi Ogawa (Japan; R), TianJing Ouyang (China; R), Steve Page (Georgia, USA; AMS), Carles Pineda Ferre (Spain; AMS), Szaniszlo Prohaszka (Hungary; AMS), Francisco Ramirez (Canary Islands; AMS), Ina Rendtel (Germany; AMS), Jean Richard (France; R), Marion Rudolph (Germany; AMS), John Sabia (Pennsylvania, USA; AMS), Paulo Raymundo Salvador (Brazil), Richard Schmude (Georgia, USA; AMS), Ton Schoenmaker (Netherlands; R), Jonathan Shanklin (Palau, Caroline Islands), Daniel Simmons (Florida, USA; AMS), Karl Simmons (Florida, USA; AMS), Matthew Simmons (Florida, USA; AMS), Stephan Simmons (Florida, USA; AMS), Wanda Simmons (Florida, USA; AMS), George Spalding (England), Enrico Stomeo (Italy; UAI), Dave Swan (England; R), Rich Taibi (Maryland, USA), Istvan Tepliczky (Hungary; R + V (AMS)), Pierre Terrier (France; R), Jurkic Tomislav (Croatia; AMS), Garfield Tsao (Taiwan; R), Diego Valeri (Italy; UAI), Gabriele Vanin (Italy; UAI), Kim Youmans (Georgia, USA; AMS), Bruce Young (Queensland, Australia; R).

Visual Results

Before we look in detail at the Leonid results, there are some important points to make. Firstly, zenithal hourly rates (ZHRs) are computed using meteor magnitude details for the shower in question, as observed during a specific year. In particular, the "population index" r is calculated from the observed magnitude distributions. Any variations in the magnitude distribution, and hence r, during the shower will affect the ZHRs. More bright meteors in the shower means observers will miss fewer meteors, and the ZHR will be closer to the observed rates. More faint meteors, and the ZHR and observed rates will diverge. Unfortunately, most observers were unable to give accurate meteor magnitude estimates during the strongest phases of the Leonids this time due to the high rates, so the r-value used is based on the magnitude distributions obtained away from the storm peaks, and was 2.6, about the same as for the Perseids and the Geminids. If more faint meteors were present during the storms, this value would increase towards 3.0 (the typical value for the sporadics); if more bright meteors, the value would decrease towards 2.0. This in turn would influence the ZHRs, increasing them if r was nearer 3.0, decreasing them if r approached 2.0.

Secondly, the ZHRs during the storm peaks were computed using 5 to 15 minute intervals to help define more accurately short-term variations in the Leonid activity, and also to help better indicate the main peak times. Normally, ZHRs are computed using the observed rate per hour, so we often call these "estimated ZHRs" or EZHRs. They are less accurate than the normal ZHRs, but still serve as a valuable benchmark for the level of meteor activity present.

Next, ZHRs are mean values, ideally calculated using individual ZHRs obtained at the same time from as many observers as possible, to give a clearer and more accurate picture than is possible using just data from a single observer. For the short-interval EZHRs in the peak over North America, often up to eight observers contributed to each datapoint, meaning these values are reasonably reliable. Fewer observers for the Pacific to Asia peak meant at best only four observers contributed to some of the datapoints, and occasionally as few as just one or two, so this peak was less ideally defined.

While ZHRs are computed values, it is best to keep the correction factors as low as possible. Normally, SPA Meteor Section ZHR data is based on those observations made with the radiant at least 20-30 degrees above the horizon, with a limiting magnitude (LM) of +5.5 or better, and where less than 30% cloud cover was present. In order to give maximum detailed coverage for the 2001 Leonids, the radiant elevation and LM constraints were relaxed somewhat, in extreme cases using data with a radiant elevation of only ~10-15 degrees and where the LM was just +4.0. However, very few data of this kind were employed, and only in cases where no serious contradiction was apparent with data from nearby times either by the same observer or others, except where no other data was available.



Despite these provisos, the Leonid activity graphs following are thought to be generally reliable and accurate estimates for what occurred. This is particularly so as the radio results, detailed later, tend to support the general character of the visual findings.

Having broached the subject of magnitudes, the first graph gives the percentage magnitude distributions for the Leonids and November sporadics, along with the corrected mean magnitude values for both sources. In total 932 Leonids and 339 sporadics are represented by this graph. While the Leonids were typically bright (50% of the Leonids were of magnitude +2 or brighter, compared to ~25% of sporadics for instance), relatively few fireballs were seen, and hardly any meteors of magnitude -6 or brighter were reported, those that were, often spotted during the storm maxima, when almost nobody was recording complete sets of magnitude estimates!

The first ZHR graph gives an overview of Leonid activity from November 16 to 19, using mean hourly ZHRs. Note the y-axis scale is logarithmic, to preserve the lower and highest activities. The twin storm maxima on November 18 (ZHRs of 1000+), are very clear, with a distinct dip between. There is a hint of the normal maximum recurring two to three times stronger than usual (ZHRs in years before the mid 1990s were ~10-15) on November 17, when ZHRs were ~35 +/-9 around 12h30m UT, and again at 19h00m UT, but there is a gap in data between these times. If it kept to its normal time, this peak should have happened at about 13h UT.

The second ZHR graph zooms in on the two November 18 storm maxima, using the short-interval EZHRs and this time a linear y-axis scale. ZHRs were picking up by the end of the European night on November 17-18, just off to the left of this graph, and had climbed to 100+ before dawn twilight set in from Spain and the Canary Isles. Rates jumped to ~300+ by 08h UT over eastern North America, as the radiant pulled higher into the eastern sky there, and climbed steadily after that towards the first storm maximum.

Consequently, this initial peak was seen well across North America, and was centred around 10h45m UT when EZHRs reached ~1970 +/-90. The next graph zooms in even closer on this maximum (again shown with a linear y-axis). The approaching and receding activity curves were relatively gentle, giving the graph quite an open shape, and rates were above half the highest value (which we call the Full Width Half Maximum, FWHM, time) for about 1h23m, so observers had plenty of time to enjoy the show. After rates dropped back below storm level, a short-lived revival to storm proportions happened again at around 12h10m UT, which was spotted from the western USA near dawn, and on Hawaii. The small number of observations by this time means this facet is not definitely confirmed however.

Despite gaps in the data over the Pacific Ocean, ZHRs dropped to ~300-500 for several hours after 12h30m UT, until things picked up again over Australia, the Far East and Asia. As the final ZHR graph here demonstrates, the second storm burst very rapidly after 17h30m UT, peaking between ~18h00m-18h20m UT when EZHRs reached ~2200 +/-330. Rising rates almost quadrupled from a dip to ~450 +/-200 to ~1700 +/-230 in the five minute interval between 17h50m-17h55m UT! This peak was significantly sharper than the North American one, with a FWHM time lasting only 50 minutes. The fascinating aspect of this second maximum was a plateau-like "shoulder" on the declining branch of the storm's activity curve. For about 50 minutes between ~18h45m- 19h35m UT, rates stayed nearly constant, hovering around storm level (EZHRs ~940 +/-170). This was great for the observers of course, who wanted the spectacle to continue for as long as possible! After this, rates dropped slowly, until by radiant-rise over Europe, ZHRs were back below the 500 mark once more, although even by the time North America was back under night-time skies on November 19, ZHRs were still well up on normal, at ~70 +/-15.

One final aspect of the visual data concerns meteor trains. While many observers continued trying to record meteor magnitudes until the storms were upon them, train data were an earlier casualty as rates began rising, so the number of trained meteors overall is very small. Some 38% of Leonids away from the storm maxima left persistent ionization trains, compared to 5% of November sporadics, but barely 10% of the Leonids in the magnitude distribution sample had the presence or absence of trains noted for them, while for the sporadics, this figure was nearer 20%, so these details should be treated with caution.

Radio Results

The following six graphs give a representative sample of the radio observations received, two each from Europe, the Americas and the Australian/Far Eastern regions, including two datasets from the southern hemisphere. Each graph shows the raw hourly counts of radio meteor echoes detected between midday on November 16 to midday on November 19 as the thick line (in the case of Ton Schoenmaker's data only, corrected for dead time, which was the amount of time lost per hour due to his system being saturated by meteor echoes). The left-hand linear y-axis shows these echo count levels - note it is not the same between graphs - while the right-hand y-axis and the symmetrical, dashed-red, curve on each graph shows the Leonid radiant elevation above the horizon for each observer's site.

Interpreting radio data like this is not easy. In general, as with visual work, a higher shower radiant elevation equates with higher detected rates, but individual radio receiver systems can produce unexpected variations, as can the location of the transmitting stations. A high radiant elevation can sometimes coincide with a drop in radio rates, which can be disconcerting for the uninitiated! Even so, the effect of the Leonids is very obvious in all the graphs, and it is possible to pick out the two main maxima on November 18, around 10h-12h and 17h-19h UT, though only Stan Nelson in New Mexico managed to catch both the North American and Far Eastern storms. There are definite signs that radio rates dropped more slowly after the second peak (Bruce Young's and Hiroshi Ogawa's data), helping to support the "plateau" in rates around 19h UT found by the visual results. The visual storm resurgence at ~12h10m UT does not appear in the radio data, though few observers were active then anyway. There are though definite signs in the North and South American data of a small peak for several hours close to 12h UT on November 17, which gives some, though inconclusive, support for the possible visual peak around the expected "normal" maximum time.

A further peak around 06h-07h UT on November 18 occurred in 60% of the available datasets. Although this coincided with the highest radiant elevation over Europe - and thus could simply be due to that fact - the North American data also shows clear signs of this. Unfortunately, too few visual data are available from this time for confirmation of it. There is a hint too of another possible radio peak towards ~22h UT on November 18, which coincides with another gap in the visual data, though there are some indications that visual rates may have picked up near this time too. More investigation of these times may be possible when the full International Meteor Organization (IMO) visual analysis is available.

Personal Recollections

The 2001 Leonids drew a lot of comments, as those with access to the electronic media especially will know. Newsgroups were flooded with notes from lucky and not-so-lucky observers, and e-mail lists including IMO-News and Meteorobs also featured recollections, initial thoughts and data summaries. SPA member John Lambert provided a representative selection of 65 newsgroup reports from individuals that he spotted, 58 from the USA, 5 from Australia and 2 from Hong Kong. It was impossible to find anyone in that set who was unimpressed by the display, even though several battled with unhelpful conditions. A few people commented on seeing rare Leonid trains of 5-15 minutes duration. Most who saw any commented on their brightest Leonid fireball. Many noted that the meteors were bright, but not especially brilliant, which echoed the thoughts of the more experienced observers. Personal recollections, photos and other results are now posted on a number of websites for those interested, including the AMS's (http://www.amsmeteors.org), the Dutch Meteor Society's (DMS's: http://www.dmsweb.org), the IMO's (http://www.imo.net), the Nippon Meteor Society's (http://www.nms.gr.jp), and the UAI's (http://www.uai.it/sez_met), for instance. Here, we look at some of the comments that reached the SPA Meteor Section directly.

In Britain, as we saw earlier, conditions were hopeless during the Leonids' best, though people here seemed to have been well-warned that even clear skies were unlikely to produce good meteor rates. A notice to this effect appeared in some of the broadsheets at least, and The Independent for 2001 November 17 featured again the infamous "star-trails" photo taken in the Jordanian desert before the 1999 Leonid storm there. This was originally captioned in 1999 as showing the Leonid storm, which of course it didn't, as there are no meteor trails on it! The message had got through - partly at least - as this time's caption read: "Stars outnumber Leonid meteors lighting up the night sky of the al-Azraq desert last year", suggesting the Independent caption-writer had slipped through a time-warp, or perhaps had had a slight spell of forgetfulness!

George Spalding in Oxfordshire, a veteran observer who saw the 1966 Leonids from Scotland, was the only observer in Britain to report any Leonids to us from 2001 - 2 in 25 minutes shortly before dawn on November 14-15! George commented on November 19: "This was just a brief check to see if there was any significant early activity. I was a bit late in rising; I had intended to start around 04h00m. So I did not get even half an hour before dawn had begun. It was a pleasure to see at least a couple of Leonids - the only two I was to see. Needless to say, I have not had a chink of clear sky since, so have nothing else to report. I wonder if there are any UK reports!" SPA Website Editor Paul Sutherland was able to provide details from the one place in Britain to get a good view of the Leonids - the fictional village of Ambridge in the BBC's Radio 4 soap opera The Archers. Paul notes: "David Archer was describing the display as Spielberg-like. It was amusing to hear Feedback on Radio 4 a few days later when various listeners wrote in to ask if the Archers were on hallucinogenic drugs!"

Elsewhere, things were not always ideal. Jay Brausch in North Dakota was able to watch on both November 17 and 19, but was clouded-out due to, as he put it, "the `well-timed' front" which ruined his skies on November 18. Even so, he remained philosophical despite missing the storm. Rich Taibi in southern Maryland decided to prepare for whatever the Leonids produced by carrying out a test run with his observing equipment on November 13, to make sure everything worked. He said: "I concluded that trying to simultaneously call out meteor magnitudes and announce WWV (UTC) time markers for the tape recorder (at 1 minute intervals), for approximately one hour, will be quite a feat of endurance and coordination! And especially when the temperature is likely to be -6 degrees C/21 degrees F! Who said meteor observing is relaxing?" The great night itself was marred by fog, but even so he enjoyed an excellent time, with plenty of bright Leonids.

In South America, Paulo Raymundo had a wonderful night on November 18: "Very bright and fast meteors of all colors were seen dropping everywhere across the sky above Reaiche Observatory in Salvador, Brazil from 1:30 to 5:30 a.m. local time (UT -2h). The show started at 03h28m UT when we saw a magnitude -6 Earth-grazer that extended from horizon to horizon. Half of the Leonids were magnitude zero or brighter and most of them left afterglows, lasting no longer than a second or two at most. Many meteors occurred within seconds of each other and fireballs also appeared to come in clusters frequently. The fireballs were the best since 1998's display, but this time there was a much greater number of red fireballs. The highest concentration of bright meteors occurred within 8 minutes: I counted eleven Leonids of negative magnitude from 05h48m to 05h56m UT. We saw so many meteors and fireballs during the four-hour period under +4.9 LM skies that we could not take pictures and count Leonids at the same time. Although astronomical twilight had started at 4:40 a.m. local time, we kept seeing fireballs until 26 minutes before sunrise, three hours before the predicted peak of the 1767 dust trail over the USA."

In the south-western USA, the dry desert and mountain areas of New Mexico, Colorado and especially Arizona must have been groaning under the weight of all the meteor observers and their equipment! Marco Langbroek had gone to Arizona with DMS teams to operate multi-station camera networks at different sites during the Leonids. They were not disappointed with rates well over a Leonid per minute all night after the radiant reached a useful elevation: "The meteors were quite bright (with fireballs up to magnitude -5), much brighter than the 1999 storm, and unlike 1999 the peak was broad, taking several hours...My highest counts (with LM +6.7) were 40-45 Leonids per minute. I found this outburst visually more attractive than the 1999 storm!!! This was definitely the best Leonid show I ever observed!" However: "Murphy struck again:...my personal dataset has a gap of about 10 minutes right at the peak! My tape recorder jammed right at that point.....:-("

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Steve Evans had also travelled to Arizona for the storm, and observed with one of a number of Czech and Dutch teams using video and still cameras there. At a beautifully dark-sky site where the zodiacal light seemed dazzlingly bright before dawn, his team had two excellently successful nights on November 17 and 18: "The maximum night itself exceeded my expectations in that the rates were higher, activity lasted longer and bright meteors were numerous, certainly more so than in 1999...my impression was that at peak activity (somewhere between 10h00m-10h30m UT) rates were almost as high as those seen from Portugal in 1999...The meteors seemed to come in bursts and at times were difficult to count. I saw 7 meteors within ~1 second on one occasion." Three composite video stills of Leonid fireballs from Steve's observations at Keams Canyon on November 18 are shown here, and you can click here fora video clip of the 12h12m UT event. His video system, christened "Emily", has an f/2.8, 28mm lens, giving a ~37-degree field of view. The brightest "star" on each image is the planet Jupiter, below the "V"-shape of the Hyades star cluster in Taurus. The Pleiades cluster (Messier 45) can be seen to the top left in the 11h03m UT image, while the two later images feature the northern part of Orion, including the bright star Betelgeuse, to the right-hand side. The misty patch on the final image - as the video clip demonstrates - is actually a flare on the camera lens due to the brilliance of the fireball.

Bob Lunsford was another observer in Arizona. After visiting Marco Langbroek's team from November 15-17, Bob met up with some other AMS watchers and a group from Europe at Mount Lemmon for the November 18 event. Skies were very poor in mid evening, but the clouds started to thin by midnight, and a series of very long-pathed atmosphere-grazing Leonids began to appear as the radiant came up, despite the cirrus. (To get an impression of what such an `earthgrazer' looks like, an all-sky image from Mauna Kea, Hawaii has just such a superb, bright trail on, at: http://concam.net/mk/mk011118/mk011118ut101257.jpg. The meteor was about magnitude -2 as seen by visual witnesses on Hawaii, according to Jim Bedient's report on IMO-News (18 November 2001: Grazing Leonid from Hawaii; Images from Kitt Peak)). Bob started watching around 12:45 a.m. local time (07h45m UT): "Rates and the brightness of the Leonids were impressive from the start. The long Leonids continued for at least another hour." Following minor problems with his tape recorder because of the cold (1 degree C/33 degrees F) after 10h UT, Bob commented that observed rates seemed to peak around 10h45m UT at ~30 per minute, then dropped somewhat, but: "The show climaxed near 11h05m when 6 near simultaneous Leonids shot in different directions creating `the spokes of a wheel' effect." Even after this, rates remained strong, and failed to drop as fast as in 1999 in Bob's estimation, and indeed he felt the show overall surpassed 1999's both for activity and bright meteors. With a magnitude -8 fireball as the wonderful dawn twilight colours were strengthening, it had been quite a night, perfectly rounded off in the mountain's observatory dome with a magnum of champagne shared between the observers before heading off to bed!

In Colorado, Gavin Edwards had a splendid night too: "It was glorious here in Boulder, easily saw around 200 per hour with several bright fireballs. Peak activity was around 3:30 a.m. [local time; = 10h30m UT] I would have said, but there were numbers around 50 per hour or greater from around 1 a.m. until 5 a.m. our time." Gavin wasn't seriously observing, but enjoyed the show visually and with 20x80 binoculars, and kept enough of a record to show observed rates in a LM ~+5 sky were easily 3-5 a minute at the peak.

Across the Pacific Ocean in Western Australia, Trevor Law had selected a site near Meekatharra, ~600 km north-west of Perth, and had a good night's observing there on November 17. Unfortunately, on November 18, the area was in the midst of a series of terrific thunderstorms: "Mostly cloudy with some spectacular lightning and the first time I've been rained on whilst still conducting the watch - and still recording meteors!" When the lightning started striking too close, Trevor darted into his car for shelter temporarily! Despite all this, in 2h17m between 17h20m-19h37m UT, he picked up almost 300 Leonids, and unlike most other observers who endured uncomfortable cold, he found "that it was pleasantly, indeed almost oppressively, warm, probably 21-22 degrees C, real T-shirt weather"! Of course, as meteor observers know only too well, nothing is ever easy. On the flight to Australia, the aircraft Trevor was on had to climb to ~12.8 km to overtop some more cumulonimbus storm clouds over Indonesia, which reduced the cabin pressure, bursting a carton of orange juice in the bag with Trevor's all-important tape recorder. Cleaning and drying the machine had no positive effect, and he was forced to use his camcorder as an audio recorder instead! This was not an ideal solution, as the camcorder used up its batteries very quickly, hence he had to abandon his concentrated watching prematurely, but it was better than not being able to properly record any of his data at all. Typical of the ingenuity observers must often employ under such unexpected circumstances certainly!

Yoko Kikuta in Japan enjoyed the Leonids on November 18 from a most evocative setting, partway up Mount Fuji, where she had gone with six astronomical friends specially to observe. Skies were marvellously clear and dark, and although Yoko commented that her eyesight isn't especially keen, she still noted nearly 900 meteors in the peak hour from 2:30-3:30 a.m. local time (17h30m-18h30m UT), and her group enjoyed a wonderful night. Yoko also commented on how the local media reported the event, which had caught everyone's attention - well almost everyone: "Newspapers reported the fantastic night. Among many reports, there was one about a car thief. He made preparations for stealing a car, and implemented his plan at 3:00 a.m. on November 19th [local time; November 18 UT]. However, so many people were out looking up at the night sky, that he was caught quite easily. He would have been successful if he had done it on a different day. Those who caught him said, `Stupid thief who didn't know about the Leonids!'"

The last word goes to Rainer Arlt, who was observing with his Arbeitskreis Meteore and IMO friend and colleague Sirko Molau. On November 23, just after getting home to discover around 500 Leonid e-mailed reports awaiting his attention, he wrote: "I was in South Korea during the last five days and was able to see a magnificent show! Activity was similar to 1999, but the high numbers lasted into the very morning." All in all, November 18 had been quite a night for all these observers, and many more.

Results and Predictions Compared

The final analysis of which predictions were more accurate for the 2001 Leonids may take time to resolve. The IMO's global analyses will be the most accurate guide for the visual activity certainly, so the comments made here, based on a much smaller data sample than the IMO's, are of neccessity somewhat tentative. However, with around 25 suggested peak times for November 17 or 18 by various authors (some differing from one another by only a few minutes), it would be helpful to see which, if any, were the more useful guides.

Two main groups made to-the-minute predictions for the 2001 Leonid maxima, Rob McNaught (former Director of what is now the SPA Meteor Section) and David Asher (M?), and Esko Lyytinen, Marku Nissinen and Tom Van Flandern (LNV), based on dust trail filament theories, the dust trails laid down by the Leonids' parent comet 55P/Tempel-Tuttle at its previous returns. This comet has about a 33-year orbital period, and each perihelion return is assumed to have laid down a single dust trail. For ease of reference we can name each trail after the approximate year it was laid down, or the number of revolutions of the comet it lies in the past. The 1-revolution trail was laid down at the comet's ~1966 return, and the 4-revolution trail in ~1866, for example. We will now look at each of the predicted dust-trail crossing times.

  • November 17d13h24m UT and 17d14h17m UT (M?): Due to the 2- and 1-revolution dust trails (~1933 and ~1966) respectively, possible ZHRs for both = 0. The first of these timings coincided roughly with the Earth's closest passage to the comet's node (the point where the comet's or meteoroid stream's orbit crosses the plane of the Earth's orbit; this is the time we routinely use for predicting most meteor shower maxima each year), around 13h UT. Our radio and visual data suggest a possible peak near this time, with ZHRs ~35 +/-9 at 12h20m UT and again at 19h00m UT. Unfortunately, the gap between these times has almost no visual data in it, though the radio data does indicate somewhat enhanced Leonid rates were probably present at a fairly uniform level over this period. Another prediction of a peak with ZHRs ~350 around 16h30m UT by Ignacio Ferrin is not confirmed at anything like this strength by the radio results.
  • November 18d10h01m UT (M?) and 10h04m UT (LNV; corrected to 10h28m UT): Due to the 7-revolution trail (~1766), possible ZHRs = 2500 (M?) or 2000 (LNV - lasting ~2 hours). The first storm peak over the USA was centred around 10h45m UT in our results, with EZHRs ~1970 +/-90, and a FWHM of ~1h23m, so the LNV prediction was closer to the mark in all respects. Peter Brown predicted a possible bright meteor peak at 11h UT, and although there was no confirmation of more bright Leonids near this time, it did fall close to the first storm peak, and there were plenty of bright meteors during the whole storm. No prediction of enhanced activity towards 06h-07h UT, as implied by the radio data, was made.
  • November 18d12h00m UT (LNV) and 12h08m UT (M?): Due to the 6-revolution trail (~1799), with possible ZHRs = 110 (LNV - lasting ~1 hour?) or 0-10? (M?). Very interesting, because this coincided with the possible visual storm resurgence at ~12h10m UT, even though this was unconfirmed by the radio reports. EZHRs were more significantly boosted than the predictions suggested.
  • November 18d14h10m UT (LNV) and 14h18m UT (M?): Due to the 5-revolution trail (~1833), with possible ZHRs = 60 (LNV - lasting ~1 hour?) or 0 (M?). This fell during a poorly-observed period in the SPAMS data, but it is intriguing that the three ZHR datapoints over this spell were ~330 +/-170 (12h45m UT), ~580 +/-80 (14h00m UT) and ~450 +/-60 (15h35m UT), which implies a possible small peak near 14h UT at least. The radio data are inconclusive about a possible maximum near this time, but this could have been subsumed into the generally active Leonid rates anyway.
  • November 18d17h38m UT (LNV; corrected to 18h03m UT): Due to the 9-revolution trail (~1699), possible ZHR = 2600, lasting ~2 hours. The later revised time coincided more or less exactly with the beginning of the second storm maximum in the visual and radio data, which fell between ~18h00m-18h20m UT, when EZHRs reached ~2200 +/-330, somewhat lower than predicted, while the FWHM time was only ~50 minutes long. The very steep increase in rates just before this peak began visually could indicate quite a sharply-defined edge to this trail's boundary. No very high activity was seen around 17h20m-17h40m UT however. Peter Brown proposed the main Leonid peak might happen near 16h54m UT, which was clearly well off the actual maximum, though EZHRs did seem somewhat stronger around 16h30m UT for a time (~890 +/-350).
  • November 18d18h19m UT (M?) and 18h26m UT (LNV; corrected to 18h20m UT): Due to the 4-revolution trail (~1866), possible ZHRs = 13,000-35,000 or below 10,000 (M?, the latter a late revision), or 5000 (LNV; lasting ~1h20m). Coincident with the end of second storm's peak visually, none of the rate predictions were at all close to the reality as witnessed by our observers, and again the FWHM of the observed storm was shorter than predicted. We should note though the ~19h10m +/-25m UT "shoulder" after the main maximum had passed may have been partly produced by activity from either the 9- or 4-revolution dust trails - or indeed both.
  • November 18d17h23m UT (corrected to 19h10m UT) and 17h26m UT (corrected to 19h10m UT; both LNV): Due to the 10- and 11-revolution trails (~1666 and ~1633) respectively, possible ZHRs = 150 for both, lasting more than ~5 and more than ~3 hours each. The corrected times picked out the centre of the post-maximum "shoulder" pretty exactly, as defined by our watchers, though rates were boosted well beyond the expected ZHR levels. As ZHRs persisted at over 200 until approaching midnight UT on November 18-19, contributions from these sources do seem plausible in helping give the declining activity as a whole a far gentler slope than that in advance of the Far Eastern maximum.

Overall, the modified Lyytinen et al. dust trail model seems to have been the better guide to when the main events occurred within the near-storm Leonid activity, and roughly how long and how strong that activity was, though these parameters were not especially close at times. Hopefully, the 2001 data will help refine the model better for future use. Although the earlier dust trail model developed by Rob McNaught and David Asher was in general less useful for the precise storm peak timings, it was a much more important piece of work, as without it, the work of the Russian scientists E D Kondrat'eva, I N Murav'eva and E D Reznikov in 1997 on exactly ths kind of modelling with regard to the Leonids could well have passed unnoticed, and we might have been unprepared for the events in 2001. For 2002, McNaught and Asher predict a single main peak on November 19 at 10h36m UT with ZHRs perhaps up to ~25,000. Peter Brown, whose modelling was clearly less well-supported by events in 2001, suggests a non-storm peak at November 19d03h50m UT. The nodal crossing time is on November 17 at ~20h UT. Lyytinen et al's predictions are still awaited.

Recent Publications on the Leonids

The following items are a selection of publications on the Leonids since our Annual Report 2000 was produced. Brief notes are given only where the title was not felt to be descriptive enough.

  • 1. "An Aerial Rendezvous with the Leonids", O. Okamura, Sky & Telescope, 101:5 (2001 May), p.137. Video observations from the 1999 Leonids made in-flight between Japan and England.
  • 2. The IMO's journal WGN, 29:4 (2001 August) has three articles on the 2001 Leonids ahead of the event, including hints for observers, the typical weather patterns for areas likely to see the best from the shower, and some new modelling of the Leonid stream.
  • 3. WGN, 29:5 (2001 October) has two technical articles on the Leonid dust trails, while a third paper tackles meteor ejection velocities from comets, using the 2001-2006 Leonid returns as a test-bed for the theory.
  • 4. "Leonids 2001: The Saga Continues", J. Rao, Sky & Telescope, 102:5 (2001 November), pp. 109-115. A brief review of recent past returns, with a preview of the 2001 and 2002 returns. The discussion includes some excellent Leonid photos from the fireball-night event in 1998.
  • 5. "Leonids 2001: A First Look", D. di Cicco, Sky & Telescope, 103:2 (2002 February), p.115.
  • 6. "Message-Board Meteor Magic", S. J. Goldman, Sky & Telescope, 103:3 (2002 March), pp.102-106. Notes from e-message boards during the 2001 Leonids.
  • 7. "The 2001 Leonids: A Great Show", D. di Cicco, Sky & Telescope, 103:3 (2002 March), pp.102-106. Initial details especially on the North American storm peak, and also on some lunar impact flashes caught on video (see the boxed item by D. Tytell on p.106), with some nice composite photos. More Leonid photos are on pp.82 and 116-118 of this issue.

Conclusion

Grateful thanks are once more extended to all of our contributors to what was a truly fascinating and successful Leonid observing campaign in 2001. Good luck and clear skies for your next observing, whether that is for the 2002 Leonids or sooner!

Alastair McBeath, SPA Meteor Section Director, Morpeth, England. 28th February 2002.

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