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SPA Meteor Section Special Report: Leonids 1998

Introduction

Leonids
The wonderful Leonid display of 1998 November 16-17 will live long in the memories of the fortunate observers who witnessed it. Data has flooded in to observing groups, most especially the International Meteor Organisation (IMO), around the world from the 1998 Leonids as a whole, and will allow the most detailed examination of the Leonids - perhaps of any meteor shower - ever. The fact that the highest rates were seen from more than half a day earlier than we originally anticipated, and persisted at a very active level for around twelve hours, had two main effects. Firstly, it caught observers by surprise, and some who had clearer skies but held themselves in reserve for the expected peak the next night were to be gravely disappointed. Secondly, unlike many previous Leonid outbursts, which have often been relatively short-lived, this event was seen well by observers from Eurasia to the Americas. Even those in the Pacific and Oriental areas enjoyed a level of Leonid activity not seen since the 1960s. Perhaps the single most obvious feature was the very high percentage of bright to brilliant meteors the Leonids produced. SPAMS figures suggest around 15-20% of Leonids on November 16-17 were fireballs, ranging up to magnitude -12/-13 for example. This meant many people living in streetlit areas, or with poor sky conditions were able to still see much of the display, and numerous casual witnesses were thrilled by the spectacle. In this Special Report, we attempt to capture some of the excitement the lucky observers felt on seeing such a tremendous night's display, as well as giving details of what happened with the shower.

The Observers

Of course, such a report would not be possible without the dedicated sky watchers and casual witnesses who thoughtfully took the time and trouble to provide the comments and data we review here. Our most grateful thanks go to every one of the following people, who reported data from across the Leonid activity period in 1998 (where P = photographic or video observations, R = radio results, V = visual data; where not stated, visual reports only were received):

Enric Fraile Algeciras (R, Spain), Rainer Arlt (Germany), David Asher (Northern Ireland), Pierre Bader (Maldive Islands), Neil Bone (England), Mike Boschat (R, Canada), Eisse Pieter Bus (R, China), John Coates (England), Heather Couper (England), Andrea Csiki (Romania), Maggie Daly (England), John Davies (England), Norman Davis (R, California, USA), Zoltan Deak (P, Romania), Maurice de Meyere (R, Belgium), Ade Dimmick (England), Carol Downs (England), Frank Enzlein (Germany), Steve Foggo (England), Doug Fox (England), Dave Gavine (P & V, Scotland), Christoph Gerber (Germany), Ghent University (R, Belgium), Andrei Dorian Gheorghe (Romania), Bob Gilmour (Scotland), Shelagh Godwin (England), Valentin Grigore (Romania), Mathias Growe (Germany), Alan Heath (R & V, England), Mark K Herbert (Alabama, USA), Kath Hodges (England), Terry Holmes (England), Simon Jenner (England), Ou Yang Tian Jing (R, China), Andr Knöfel (Mongolia), John Lambert (England), Will Kelsey (R, California, USA), Daniel Köhn (Germany), Werfried Kuneth (R, Austria), Trevor Law (Western Australia), Alan Longstaff (England), Bob Lunsford (California, USA), Hartwig Lüthen (Mongolia), Andrew Mark (Scotland), Tony Markham (England), Alastair McBeath (England), Peter McBeath (P & V, England), Tom McEwan (Scotland), Kieron McGrath (England), John Meyer (R, Arizona, USA), R B Minton (P, R & V, New Mexico, USA), Sirko Molau (Mongolia), Neil Mortimer (England), Sven N ther (Germany), Sadao Okamoto (Japan), Guy Ottewell (South Carolina, USA), Ingo Reimann (R, Germany), Ina Rendtel (P & V, Germany), Jürgen Rendtel (P & V, Germany & Mongolia), Petra Rendtel (Mongolia), Tony Rickwood (England), Ian Rigney (England), Joan Robinson (England), Maurice Robinson (England), Vanya Rodiger (Croatia), Paul Roggemans (Belgium), Andy Salmon (England), Fred Schaaf (New York, USA), Ton Schoenmaker (R, Netherlands), Amanda Scott (England), Jonathan Shanklin (in flight between England and Ascension Island), Dierdra Shepherd (Western Australia), Jamie Shepherd (Western Australia), Chikara Shimoda (R, Japan), Hendrik Sielaff (Mongolia), Adrian Sonka (P & V, Romania), George Spalding (England), Ulrich Sperberg (Cyprus), Jorg Strunk (P, Germany), Paul Sutherland (France), Melvyn Taylor (Cyprus), Pierre Terrier (R, France), Axel Thomas (Germany), David Todd (England), Manuela Trenn (Germany), Mihaela Triglav (P & V, Slovenia), Valeriu-Mihai Tudose (P & V, Romania), James Vanderpool (England), Björn Voss (Mongolia), Andrew Walker (Scotland), Peter Ward (England), David Weldrake (England), Robert S White (R, England), Ilkka Yrjölä (R, Finland), Wim T Zanstra (R, Netherlands), Florian Zschage (Mongolia).

In addition, thanks are also due to Chris Steyaert, who provided copies of many of the radio observations in Radio Meteor Observation Bulletins 64 and 65 (December 1998 and January 1999 respectively), and Ina Rendtel, who provided much of the German and Mongolian data from the Arbeitskreis Meteore observers in their journal Meteoros vol.1, no.12 (1998). Personal Recollections from November 16-17

Most of our contributors live in and observed from Europe on November 16-17. Only Trevor Law had sought clearer skies in the summer hemisphere of November by going to Western Australia with Dierdra and Jamie Shepherd, all from the UK, though Jonathan Shanklin, en route to the Antarctic that night, came very close to observing through his aircraft window from south of the equator. He was stopped by the dawn twilight coming up, while still around 4y north latitude at 05:48 UT, but he continued to see occasional bright Leonids after this until just a few minutes before dawn. Even under such difficult observing circumstances, Jonathan logged about 450 Leonids in 3h20m, many of them very bright, and commented that "it was certainly a spectacular sight. Several colleagues on the plane were also able to enjoy it and one estimated that he saw a meteor every 10 seconds when rates were highest". This level of observed activity was comparable to what watchers across Europe and North America saw with an unobstructed view of the sky, an indication of the numbers and brightnesses of the Leonids about.

In Western Australia, Trevor, Jamie and Dierdra were clouded-out completely after local midnight on November 16-17, but Trevor noted that a tremendous storm was seen the following night from the city of Perth. This was not of Leonids, however. Instead, an unseasonal thunderstorm hit, producing golf-ball sized hailstones, continuous thunder, and lightning flashes about once per second at its height. Luckily, Trevor's party were around 700km further north at the time, near Shark Bay, but even there, clouds prevailed, so they drove over 400km north-east to find better skies on November 17-18. Observed rates were still good for them, at 3-6 Leonids per minute at times, but with hardly a fireball all night, it was a somewhat disappointing contrast with what happened over their homes in Britain. Even so, the one Leonid fireball that did chance-by, magnitude -4, appeared just over half an hour before sunrise, in deep twilight!

Of course, not everyone was lucky in seeing something of the display. The weather was always liable to be a problem in the northern hemisphere's early winter, with reports indicating parts of north-west England and Northern Ireland were completely clouded-out or had fog on the critical night, for instance. In inland South Carolina, Guy Ottewell reports fog ruined any chance to see the Leonids at all from there too, as Mark Herbert also discovered in Alabama (a nuisance, as he had travelled there from the clearer skies of his home site in Somerset, England). In Germany, the heavily overcast sky was a severe problem. Rainer Arlt and Manuela Trenn drove across the country for a total of 10 hours on November 16-17, hunting for better skies, but managed just one nine-minute observation in a cloud gap, even so seeing seven Leonids in that time. Rainer comments that the next night had only marginally better conditions, despite his having driven around 250 km from Berlin into Lower Saxony. He was permitted a thirty-minute watch for much poorer Leonid rates. Ina Rendtel, who made a similar trip that night, also made similar comments.

Several observers picked the wrong night to observe, after relying entirely on the predicted peak time, and a few decided against watching in clear skies on November 16-17, expecting another clear night and better rates on November 17-18. In many cases, such people saw only clouds the next night, and were disappointed not to have observed when they had the chance. Although disheartening, such a mistake is good experience, and is also an error most experienced watchers have made in the past. George Spalding, a veteran who also watched the 1966 Leonids from Britain, explains his feelings when he woke at 01:00 UT, ahead of the alarm he had set, and saw there were some breaks in a rather cloudy sky: "I was not too keen to venture out, but then recalled the past opportunities I've wasted only to be clouded out later". If the Leonid storm does occur in 1999, at least those who did so made their mistake before that happened! One poor soul, who I shall leave nameless, intended to observe on November 16-17, but then slept through the alarm clock ringing...

Those who could observe on November 16-17 all had a wonderful night. Even around radiant-rise from Europe, Leonids were already apparent. John Davies in Lancashire spotted a wonderful magnitude -5/-6 probable Leonid fireball with an exceptionally long path as early as 22:20 UT on November 16, and several other UK watchers were noting Leonids from around 23:00. Maurice Robinson spotted three in a matter of five minutes while walking his dog, despite a fairly cloudy sky, for example. The following are some brief quotes from the reports received: Four of the meteors were so brilliant they illuminated my garden (John Coates); It was very exciting! (Maggie Daly); a wonderful celestial gala evening (Carol Downs); A wonderful display, with many bright and colourful meteors (Doug Fox); Photographed 22 [Leonids] in 1 hour on 16mm lens, 7 of them on 1 frame. That's more than in my entire meteor watching career! (Dave Gavine); That wasn't a meteor shower; it was a fireball shower! (Andrew Mark); Conditions were already deteriorating by the time that I reached my observing site...However, I started observing and five meteors in the first minute is not at all bad! (Tony Markham); meteors averaging 3 or 4 per minute...A number of meteors (not seen) lit up the entire sky (Peter McBeath); After 3 months of almost non-stop rain, 16-19 November were the first transparent nights...in a long time. I was out, just for a look...before the assumed maximum...there were many bright Leonids (Paul Roggemans); Even now, I can scarcely believe my luck at having seen such a spectacle...It was a cold night, but I hardly felt it as I was entertained both by the number of meteors and their brightness (George Spalding); Some "cracking" trains seen - and there are no railways in Cyprus!! (Melvyn Taylor); awe-inspiring (Peter Ward).

Many observers - including myself - enjoyed their best night of meteor observing of all-time, in terms of meteor numbers in so short a time, overall meteor tallies, and the number of bright meteors around. Flashes lighting up the sky from otherwise unseen meteors were commonly reported from numerous places, confirming the ability of a spectacular Leonid outburst to awaken people from their beds behind closed curtains, as happened in 1833, in days before light pollution. Good as it was, one observer, R B Minton, commented: "This display was the 2nd best meteor display I have witnessed." His reason? "The best was the Leonid display of 1966 while I was living in Las Cruces" (New Mexico, USA)! R B and his wife had turned their home into a Leonid observing station for the 1998 event, recording what happened visually, by video, photography and forward-scatter radio.

Several people commented with surprise at the silence of the 1998 Leonids, despite so many very bright meteors, which tends to give the lie to the supposed psychological explanation used by those who wish to ignore meteor sounds, both of the simultaneous electrophonic type, and the acoustic sort. Surely with so many bright events, somebody should have imagined they heard something if any kind of psychological effect of this sort really happens? R B Minton's comments on this point are very telling: "in all 600 (or so) observations of meteors, my wife and I never heard any kind of meteor noise. No boom, hiss, crackle, or other kind of noise...I viewed the November 17, 1966 Leonids from 1:00 a.m. to 5:30 a.m. MST [Mountain Standard Time = UT-7h] and also never heard meteor noises. But in this case, the sample size must have been closer to 200,000!!!" Meteor noises of whichever kind seem to require deeply-penetrating meteors, whereas even bright Leonids occur higher in the Earth's atmosphere than most other meteor showers thanks to their greater relative entry velocities.

Superb, long-lasting trains were another hallmark of the night, with most observers under reasonably clear skies seeing one or more lasting for upwards of five minutes, twisting into an "S"-shape or a ring before fading away. Valentin Grigore reported trains up to 25 minutes in duration, enough time to photograph or video them. One that R B Minton videod "expanded into a hollow tube and showed spiral structure in several places. Several others showed a hollow-tube appearance after 1 minute." Most of the videod trains were brightest near their termini, and R B comments that in about half the cases he recorded bright "blobs" occurred where late flares had happened in the meteor's flight. "These blobs would frequently split into 2 or 3 pieces, with perhaps 1 remaining smaller and more spherical than the rest. These multiple blobs would then exhibit a common motion". However, the individual "blobs" also showed a differential motion between one another, and R B suggests, using the analogy of high-altitude barium releases he had previously witnessed, that perhaps the electrical charge of each "blob" helped determine its behaviour.

The Meteor Group of Astronomical Association Javornik in Slovenia also managed to record some long-lasting trains photographically, and Mihaela Triglav sent in some excellent photos of two, one of which lasted for around 11 minutes after a magnitude -12 Leonid. It distorted into a magnificently serpentine coil before fading away, which as Mihaela said really did resemble a dragon (see my articles on this subject in Popular Astronomy, April 1997, p.12, or WGN 25:1, 1997, pp.34-36).

Many observers discussed the coloured nature of the Leonids they had seen. Such colours are not unexpected with meteors of magnitude +1 and brighter, which covered a very high proportion of the Leonids on November 16-17. Green was certainly popular, in some of the colour photos as well as the visual sightings. R B Minton noted that all 13 Leonids he photographed like this showed green in their upper (earlier) stages, despite his using several different cameras, lenses and films. This could have resulted from 557.7nm oxygen emission, which is known to occur with high-altitude meteor ablation. Tony Markham also noted another effect: "Two of the trains showed strong colouration for the first second - red/yellow/green/blue bands - like a spectrum. Both were very low in the sky - was this an atmospheric effect (red was lowest) or related to the meteors themselves?" Tony experienced problems because of a lot of cirrus cloud during his watch, so it may be some kind of corona effect due to diffraction, or halo effect due to refraction, occurred in the ice-crystal clouds. Both effects have been observed with the Sun, Moon, planets and even bright stars like Sirius at times, so either could be suitable explanations.

As we might have expected, it was a cold night across Europe and parts of North America. Temperatures across the clearer parts of the UK were around, or below, freezing - it was -6°C at Morpeth by dawn, for instance, with a white frost over everything, including the outer layers of my observing kit! This was nothing compared to conditions in Mongolia, from where the leader of the German Arbeitskreis Meteore expedition Jürgen Rendtel reported temperatures dipping to -27°C, or -34°C above the snow! Jürgen went on to say: "The only disadvantage of the beautiful winter landscape (~20cm snow) was the noise of the snow... We even heard wolves howling - in the distance!" Such colder temperatures were not to everyone's liking, even in the relatively milder Europe. John Lambert in northern England found his car frozen solid, so ended up stuck in his garden at home with a streetlamp directly in front of the Leonid radiant! Even so, he saw numerous Leonids, some bright enough to light up the sky in spite of the obvious man-made lighting problems.

Three UK observers unable or unwilling to risk the cold watched from indoors, but even so, still saw around 30-50 Leonids per hour at times, and were greatly cheered by the view. One of these, Bob Gilmour, lives in Wick in the northernmost part of Scotland, and deserves a special mention here as being the oldest observer to report his watch from November 16-17, as he was nearing his 83rd birthday at the time. There can be few more superb ways to celebrate such an event for any astronomer than with a display of meteors like the 1998 Leonids.

Leonid fireballs continued raining down into strong twilight across Europe, and some were seen shortly before, or after, sunrise, giving the observers a real feeling of being part of a greater, global, meteor community, knowing they were "passing the baton" of observing on to watchers further west in Europe (from eastern Europe), or across the Atlantic to North America (from western Europe), who in turn saw still excellent activity fading into their dawn as the Leonid "torch" was passed back to the Far East and Asia. As George Spalding put it, it was like being part of one big family, a "United Nations" of observers.

Oh the Leonids! Some comments by Shelagh Godwin

Yes, everyone was ready to watch out for the Leonids on November 17-18. They'd been primed to do so by the media, and not a few astronomers (though SPA members had been warned to use both November 16-17 and 17-18 by Alastair's article in July 1998's Pop.Astron., pp.9-11). But how many heard this little bird on BBC Southern Counties Radio on Monday morning? "Get out there on Tuesday morning because there could be a chance of some early activity from the shower, and it looks as though the clouds could close in by Tuesday evening" (which in the event they did). Well, I did follow my own advice, setting the alarm for 02:45, not earlier because I was nursing a cold and had been feeling groggy earlier in the evening. I knew I had to get better before singing in a concert in Winchester the following Saturday.

I hadn't reckoned with the fog: it closed in about 4 a.m. I had hoped to stay out until dawn and thought afterwards, "Why didn't I think of getting into the freezing car and driving to somewhere where it might have been clearer?" Anyway, as I wriggled into my sleeping bag and adjusted my white torch inside a brown grocery bag (why did my red torch have to pack up just the day before, and why was it so obsolete that I couldn't for love nor money get another battery for it?), a brilliant bright flash across the sky cast shadows. I couldn't see where the flash was: it was probably below my horizon. Although by this time it was 03:12 the Leonid radiant was only just emerging from the fog and murk.

During the next 50 minutes or so I spotted some amazing events: flashes near the radiant, one of which was almost blinding and cast shadows; exceedingly fast bright (and not so bright) meteors, and more flashing through the haze. It was very difficult to estimate the brightnesses of the fireballs, particularly once Jupiter had set. Activity was so intense that while I was noting down, and in a couple of instances plotting, one meteor, another, equally spectacular, appeared. White was the order of the night, perhaps a bit of yellow in places, and the blinding flash could have had a tinge of blue to it. But since much of the sky was a yellow ochre colour anyway, the more subtle colours could well have been lost.

What of those who travelled to the Far East to witness a hoped-for outburst? They saw enhanced Leonid activity, but not as intense as over Europe. IMO reports show that what we saw in Europe was not the Leonid storm peak, but a very strong background component of exceptionally bright meteors that occurred several hours earlier than predicted, and lasted for 12 hours at least. There may be a good chance of seeing it again in 1999. There is also a good chance that a storm of fainter meteors will occur over Europe during the night of 1999 November 17-18. But I'm not going to wait for that. I'll be out the previous night, just in case!

Our final set of reminiscences comes from former JASMS Director George Spalding, whose report of his recollections of the 1966 Leonids over Scotland featured in our 1997 SPAMS Annual Review.

George Spalding's personal impression of the 1998 Leonids

Even now, writing on 1998 November 19, it hardly seems believable that I have witnessed my best ever meteor shower in the UK in 34 years of observing. The peak of the Leonid shower was scheduled for an estimated time of 1998 November 17d 19-20h, best visible in the Far East. However, especially since the forecast for November 17-18 at my site looked rather unfavourable, I certainly planned to cover the night of November 16-17, to monitor the expected rise in activity, and it's just as well I did.

There was rather a lot of cloud in the evening of November 16 so I went to bed at 22:00 UT, having set the alarm for about 02:00 UT. When I woke early at about 01:00 UT, there was still lots of cloud. But luckily, I decided to get outside and start observing right away. At the start the stars in Leo, still at a low elevation, were only barely visible, and there was a fair bit of cloud in the east. But it was soon apparent that the shower was much more active than on the previous night.

After only 10 minutes of watching, at 01:31 UT, came one of the highlights of the night. A magnitude -3 Leonid raced through Auriga and left a train which persisted over 3 minutes; it gradually widened as it slowly faded, and slightly twisted. Long duration trains lasting many seconds were to be a feature of the display. It was also evident from this first watch (01:21-02:21) that there were many bright Leonids, negative magnitudes being quite common.

For the second watch (02:35-03:35), I shifted round to look south-west from then on, rather than east as previously. This second watch probably had the best conditions (LM +5.4) as the clouds dispersed, though it was hardly ideal. Another great meteor, of magnitude -5, flashed at 02:57:30 and its train was of 10 seconds duration, followed within a minute by a magnitude -2 with train 5 seconds. Then at 03:09 a Leonid of magnitude -5 was seen in the low south-east, train 7 seconds. Some very minor cloud appeared in the west in the last 15 minutes of this watch.

My third watch (03:51-04:16) was shortened as diffuse cloud and fog grew steadily, though meteors continued to be visible behind the cloud. This watch saw my brightest Leonid of the night, magnitude -6, which appeared at 04:05:30; the train was 3 seconds, and there was a vivid green as the event exploded. When I had to stop the watch at 04:16 I thought that that was the end of my work. However, as I took a coffee break, the fog began to lift again, and I was able to start my fourth and final watch at 04:33.

This watch (04:33-05:23) proved notable for good rates and many negative magnitude meteors. For example, the period 04:49 to 04:50:30 saw 11 meteors. Also, 6 of the 8 meteors noted between 04:50 and 04:51:30 were brighter than magnitude 0. The train that accompanied a magnitude -4 Leonid at 04:59 lasted at least 13 seconds. Finally, the fog returned to prevent my completion of a full hour. The watch had to stop at 05:23, but only about 45 minutes remained till Nautical Twilight would start. As thick fog came down, I had time to reflect on a truly memorable night.

The total of 271 meteors in 3h15m watching was the highest number of meteors I've noted in a single night in the UK, and also the highest observed rates. November 17-18 and 18-19 proved to be hopeless for observing, the former owing to fog, the latter owing to cloud. Roll on 1999 November!

Preliminary Leonid Analysis

Using results submitted to the SPAMS, the details published by Rainer Arlt in "Bulletin 13 of the International Leonid Watch: The 1998 Leonid meteor shower" (WGN 26:6 (1998), pp.239-248), plus further discussion with leading IMO analysts Rainer Arlt and Jürgen Rendtel, this section gives an overview of what the Leonids did as seen by observers across the world. The SPAMS database contains at least some information on 10136 Leonids seen in November, in 261h of visual observing. Thirty-nine meteor trails were photographed (35 Leonids, plus several Leonid trains) in ~150 camera-hours, not including comments on video recordings secured by several people too. In addition 4724.5h of radio observation were carried out.


leozhr.gifThe ZHR graph shows how Leonid activity behaved. It is a composite based on IMO data, but slightly different methods were used to compute the near-peak rates compared to the lower activity away from this time. This was necessary to allow for the very large number of bright meteors seen near the 1998 Leonid maximum. Unlike most meteor shower peaks, almost no Leonid meteors fainter than magnitude +4 were seen. This was not because observers were ignoring the fainter meteors; photographic and video results confirm there was a genuine absence of fainter Leonids at this time. The highest ZHR was ~340 ±20 at solar longitude 234.5° (November 17 around 01h30m UT).

On the descending branch of the shower's activity, around solar longitude 235.31° (November 17, 20h30m UT), a secondary peak can be seen, when the ZHR reached ~180 ±20 for a short time. This peak was composed of a significantly fainter group of meteors than those seen with the highest fireball peak. This was the peak all earlier estimates had concentrated on predicting, and if a Leonid storm had happened in 1998, this was the time it would have done so. It occurred about 1,h later than previous Leonid returns had suggested. By contrast, the earlier, higher, peak had not been detected at all in recent years. After the event, some evidence was found suggesting something similar may have happened in 1965, ahead of the last great Leonid storm, but the significance of the 1965 data was not made clear when it happened, largely because no global-scale meteor coverage was then taking place.

leo-data.gif
The difference in the two meteor populations (fireball peak to non-peak) was very marked. An indication of this can be seen in the magnitude distribution graph to the right here, based solely on SPAMS observations made under skies where the limiting magnitude was at least +5.5, with less than 20% cloud present. This shows the percentage distributions in each magnitude interval (note all meteors of magnitudes -3 and brighter and +4 and fainter have been grouped together for simplicity) for November 16-17, and all other nights Leonid observations were possible. Unfortunately, only a small number of Leonid magnitude estimates (125) were available away from November 16-17 (when 615 magnitude estimates were on-hand), but even so, the two distributions are clearly dissimilar. This is reflected again in the corrected mean magnitude for the Leonids, which was +1.3 on November 16-17, compared to +2.7 on other nights. For comparison, the November sporadics' mean magnitude was +3.7.

Many people found observed rates so high on November 16-17, with 6-8 Leonids a minute quite frequently, that they had great difficulty in just trying to give accurate magnitude estimates and timings for the meteors seen. As was stressed in all Section literature before the event, however, the most important aspects of the shower were recording the meteor magnitudes and keeping a note of the meteor numbers over short time intervals. The majority of Section observers tackled the difficulties presented by the 1998 Leonids magnificently. The downside to this was that almost nobody managed to give plotted positions for the fireballs they saw. A total of 227 individual fireball sightings were submitted to the Section from November 16-17, through even until after sunrise on the 17th. From 1-3 fireballs were seen every minute from 05:14-05:24 UT, for instance, ranging between magnitudes -3 to -10, with 4-5 fireballs a minute at times being not uncommon all night! The spectacle was so wonderful, this loss of data really matters quite little, and it would probably have been impossible to make any sensible computations concerning the fireballs anyway, with so many of them raining down every few minutes for the majority of watchers.


Ras 10 minute radio meteor echo countsAside from visual and photographic work, the radio observers were also busy in force, with all those who were active during the Leonid epoch recording a wonderfully high spike during the Leonid radiant's effective visibility from their sites. Robert White's raw ten-minute counts are given here, during the 24-hour period from 18h UT on November 16 to the same time the following day. The near-continuous high activity is almost entirely due to the Leonids, as other results confirm, and shows how long-lasting the fireball peak really was, with observers across North America who had better skies continuing to enjoy similar rates to what had been seen across Europe earlier on November 17. The dip around 04h UT is most likely an artifact due to the direction of Robert's antenna, since visual reports and other radio data show undiminished bright Leonid rates at this time.

A particular casualty of the very high visual rates was the train details. Although around 40% of Leonids left persistent trains that could be recorded by observers, this is almost certainly an under-estimate. From my own observing on November 16-17, I judged I managed to record trains for between half to two-thirds of the Leonids I saw. From sites affected by hazy, foggy or partly clear skies, the train numbers were lower, and in some datasets it was even possible to see that the conditions had also reduced the apparent visible train durations. Consequently, it is likely some 60-80% of the Leonids, especially those on November 16-17, actually produced detectable trains. It would be misleading to try to analyse these in further detail, but some superb photographs were secured, and many observers were delighted to see trains lasting five minutes or more several times during the night. The sporadic train population was 7% for comparison.

A massive THANK YOU is again due to everyone who contributed data, whether a casual, if overjoyed, report of impressions, or a single bright meteor sighting, through to fully detailed observations. All are gratefully thanked and congratulated on their efforts.

Prospects for 1999

The prospects for a Leonid storm were always going to be more favourable for 1999 than 1998, judging simply from the Earth/Comet Tempel-Tuttle orbit encounter geometry, and that remains true in the light of events in 1998 November. The short-lived minor increase in rates at around the predicted maximum time in 1998 indicated a concentration of new particles lying close to the comet's orbit, and we should hopefully encounter that concentration again at some point between 01-05h UT on 1999 November 18. This is not a guarantee of high activity, of course, nor is the timing certain. If another prolonged fireball episode occurs at the same time as 1998, that should be seen around 08h UT on 1999 November 17, but if it is comparable to the 1998 event, it could be seen for several hours before and after this time too. All observers would be advised to watch for as much of the night on November 16-17 and 17-18 as possible, as a result. It is important that other nights during the Leonid activity should not be ignored. Leonids can be seen from November 14-21 in most years. It is possible that other unexpected events may await detection from the shower, and with the waxing gibbous Moon near the expected peak this year, the most favourable times for Leonid observing - midnight and afterwards - will be free from moonlight interference.

Coping with very high meteor activity

We here reproduce the notes first issued last year as a special SPAMS information sheet, just in case the Leonids do produce something exciting in 1999.

The most vital thing on being the fortunate witness of very high meteor rates is not to panic! Recording what happens as accurately as possible is an important aspect of the event for many people, but never forget to take time out to enjoy the spectacle too.

Normal visual meteor watch details should be recorded, as outlined in the Section's booklet Observing Meteors, for as long as possible. As activity increases, this will become impossible; you must decide for yourself when that point is reached. After that, the most important features to record are the magnitudes of the individual storm meteors only. Try to ensure that you note the time at least every five to ten minutes, so your counts can be correlated, and an approximate rate worked out later. Timings for individual meteors, except particularly brilliant fireballs, are not necessary. There may come a point when recording all the meteor magnitudes you see is no longer feasible either. In this case, only maintain details on the brighter events - magnitude +4 or +3 and brighter - reducing the magnitude level further if necessary, even to magnitude 0. As activity decreases, you can then reverse this procedure.

Alternatively, you can reduce the area of sky you are counting meteors in. Pick a well-known, and easily recognisable constellation of reasonable size, such as The Plough, the Great Square of Pegasus, or Orion, for instance. Any meteor that crosses through your chosen asterism should be counted, and the magnitude recorded. A better variant is to have a camera available. Suitable equipment for meteor photography is also discussed in Observing Meteors, and these guidelines should be followed here. Once you reach the point where you must reduce to counting only magnitude +4 or +3 meteors, providing the sky limiting magnitude is at least +5.0, stop visual observations, and continue to observe photographically. Make this change only when you need to count just magnitude +1 or 0 meteors if the limiting magnitude is worse than +5.0. Aim the camera opposite the shower radiant in the sky (unless this will mean a bright light source like the Moon will be on the frame), at around 60y-80y elevation above the horizon. The higher the radiant, the lower the camera field centre should be. Ensure the horizon or other obstructions do not block any part of the field. A shot or two directly at the radiant would also be interesting for your photo album.

The exposure durations will depend on how high activity is. If it is not too high, use up to a 10 minute exposure, but reduce this to about 2 minutes if an extraordinary storm happens. Try to avoid changing the film if at all possible. This will necessitate some rapid mental arithmetic to maximise your options, of course! Timings of every exposure's start and end must be recorded to at least the nearest second. Prints or negatives should also be submitted for full analysis. Remember to supply camera and exposure details for all your photographic work.

A video camera can also be useful, even a normal colour camcorder, although they are not especially sensitive for night-sky work. Use the widest possible aperture, manually focus the lens at infinity (autofocus mechanisms frequently will not operate when aimed at the dark sky). Use the time display tuned to its finest possible increment. If you have no timer, deliberately cover the field several times at specific instants (and note the exact times of these), or add an accurate verbal time-base using a microphone onto the video tape. Use high-quality tape only, set at the highest recording tape-speed. Mount the video camera on a tripod, either firmly fixed, or if a clock-driven mount is available (such as for a telescope), on that. Aim the field as for a still camera, but ensure at least three recognisable stars can be seen. Details on every meteor recorded (time, direction and estimated magnitude) should be submitted after you have reviewed the tape afterwards at least twice. It is preferable if you can also submit a copy of your tape (not the original, in case of damage or accident in transit) with your report too, ideally in VHS format. Also give all other normal watch details as appropriate (such as your name and site location).

Recent Publications on the Leonids

For those interested in learning more about the Leonids, the following is a selection of useful papers and articles on the shower published during the last twelve months, and not already mentioned. Brief notes are given only where the title was not felt to be descriptive enough.

  • "SPA Meteor Section Results: November-December 1997", A. McBeath, WGN, the Journal of the IMO, 26:3 (1998 June), pp.143-146.
  • "Bulletin 12 of the International Leonid Watch: Final results of the 1997 Leonids and prospects for 1998", R. Arlt & P. Brown, WGN, the Journal of the IMO, 26:4 (1998 August), pp.161-165.
  • "The Leonid meteors: Compositions and consequences", D. Steel, Astronomy & Geophysics, 39:5 (1998 October), pp.5.24-5.26. Includes details on scenarios for satellite damage due to the Leonids.
  • "Prospects for two upcoming periodic meteor showers", J. Rao, WGN, the Journal of the IMO, 26:5 (1998 October), pp.192-216. The showers being the 1998 Draconids and Leonids.
  • "The night of raining fire", R. Sanderson, Sky & Telescope, 96:5 (1998 November), pp.30-36. A lively historical review of the 1833 Leonids as seen from America.
  • "The return of the Leonid meteors", J. Rao, Sky & Telescope, 96:5 (1998 November), pp.38-44.
  • "Leonid fireballs dazzle the world", G. Seronik, Sky & Telescope, 97:2 (1999 February), pp.123-124. Includes some excellent photos - see also the "Gallery" section in this issue of S&T for more wonderful colour photos from the 1998 shower.
  • "Images of a Leonid meteor train", Astronomy & Geophysics, 40:1 (1999 February), p.1.4. The train was from an almost point-source meteor.
  • "Awaiting the storm", J. Rao, Sky & Telescope, 97:3 (1999 March), pp.48-50. A brief review of the 1998 Leonids and a look-ahead to the 1999 event. See also p.136 in this issue for another Leonid train sequence of photos.

Conclusion

Little more now remains but to thank once more everyone who contributed to making this report possible, and to wish everyone good luck and clear skies for the coming meteoric events this year, including of course the Leonids in November. Your observations and reports are eagerly awaited! I would also like to take this opportunity to thank all those who have sent good wishes in letters and cards in recent months during my recent, and regrettably still on-going, period of illness. Your kindness and thoughtfulness have been greatly appreciated.

Alastair McBeath, Morpeth, 1999 March.

For copies of all SPA Meteor Section publications, please contact our Assistant Director, Shelagh Godwin, at:
14 Chestnut Way, Godalming, Surrey. GU7 1TS.
Email: SGodwin286@aol.com

For queries about meteors generally, and when submitting your data, please write to the Director, Alastair McBeath, at:
12A Prior's Walk, Morpeth, Northumberland. NE61 2RF.

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