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The long-awaited Leonid storm did happen after all on 1999 November 17-18, with European observers - including some lucky people in northern Britain - well-placed to catch it. Observers in the Near East and North Africa from Jordan and Israel to Morocco and the Canary Isles, along with more in France, Spain and Portugal enjoyed the clearest views, meaning that within only a month of the event the International Meteor Organization (IMO), was able to present a preliminary global analysis on the storm based on more than a quarter of a million meteors! Unlike the 1998 Leonids, the storm was relatively poor in fireballs, but made up for it in sheer meteor numbers, with visual observers at clear-sky sites seeing upwards of 30-40 Leonids a minute nearest the storm's height. This Special Report tries to give a flavour of what it was like to see the storm, as described by the lucky observers, and what it was like to miss it for the unlucky ones, as well as providing details of what happened with the shower.
As normal, no report would be possible without the dedicated meteor watchers and more casual witnesses who thoughtfully took the time and trouble to provide the comments and data reviewed here. Grateful thanks are due to every one of the following people who reported their view of the 1999 Leonids. Abbreviations in the lists are "Ph" = photographic observations, "R" = radio results, "Vi" = video data. No additional letter indicates visual reports only were received.
UK-only observers (in England unless noted): Pamela Armstrong (Pitlochry, Scotland), Mark Bailey & others from Armagh Observatory (Ballygawley, Co. Tyrone, Northern Ireland), Lyndall Barbour (Boreham, Wiltshire), Matthew Barrett (Witham, Essex), Neil Bone (Apuldram, West Sussex), Tom Crann (Derwent Reservoir, Durham/Northumberland border), Clive Down (Bridgend, South Wales), Steve Dunn (Hale, Manchester), Keith Edwards & colleague (Dundee, Scotland), Guy Fennimore (Snowdonia, North Wales), Ami Frydman (London), David Frydman (London), Dave Gavine & 2 members of Edinburgh AS (Edinburgh, Scotland), Shelagh Godwin & members of Guildford AS (North Downs and Godalming, Surrey), Peter Grego (Rednall, Birmingham), Lucy Hague (Holm, Orkney Islands), Chris Hall & members of Macclesfield AS (Gradback, Staffordshire Peak District), James Hamilton (Stockport, Cheshire), Eva Hans (South Shields, Tyne & Wear), Kath Hodges (Hale, Manchester), Mike Holmes & others (Edinburgh, Scotland), Martin Ince (London), John Lambert (Pegswood, Northumberland), Jeff Lashley (Vi; Derwent Reservoir, Durham/Northumberland border), Richard Livingstone (Abergele, North Wales), Tony Markham (Leek, Staffordshire), Nick Martin & 3 members of Ayr AS (Bonnyton, Ayr, Scotland), Michael Martin-Smith (Ph; Hull, Humberside), Alastair McBeath (Ph; Morpeth, Northumberland), Peter McBeath (Ph; Morpeth, Northumberland), Roy McBeath (Wimborne, Dorset), Simon McBeath (Blandford, Dorset), Tom McEwan (Glengarnock, Ayr, Scotland), John McFarland & others (Armagh Observatory, Northern Ireland), Michele Minett (Stockport, Cheshire), Jacqueline Mitton (Cambridge), Neil Mortimer (Devizes, Wiltshire), Dave Newton (Ph; Derwent Reservoir, Durham/Northumberland border), Michael Oates (Prestwich, Manchester), Tom Patton (Livingston, Scotland), Trevor Pendleton (Skegness, Lincolnshire), Ian Ridpath (Dunstable, Bedfordshire), Ian Rigney (Failsworth, Manchester), Maurice Robinson (Morpeth, Northumberland), Graham Rule & others (Edinburgh, Scotland), Neville Saunders (Gower Peninsula, South Wales), Paul Saunders (Ph; Gower Peninsula, South Wales), Brian Sidney (West Woodburn, Northumberland), George Spalding (Denchworth, Oxfordshire), Stanley Toyn (Exmouth, Devon), Bill Ward (Glasgow, Scotland). Additionally, media reports from Hunstanton, Norfolk and Canterbury, Kent were also forwarded to us.
Overseas observers: Enric Fraile Algeciras (R; Spain), Claire Arbonnier (Italy), Rainer Arlt (Spain), Stan Armstrong (Ph; Morocco), David Asher (Jordan), Pierre Bader (Germany), Godfrey Baldacchino (Malta), Michael Boschat (R; Canada), Jay Brausch (North Dakota, USA), Massimo Chianese (Italy), Tim Cooper (Belgium), John J Costello (Ph; Philadelphia, USA), Maggie Daly (Ph; Canary Islands), Martin Galea de Giovanni (Malta), Maurice de Meyere (R; Belgium), Jack Drummond & others (New Mexico, USA), David Dunham (Maryland, USA), Andrew Elliott (Vi; Portugal), Frank Enzlein (Germany), Steve Evans (Ph, Vi; Portugal), Mildred Formosa (Malta), M Gerding (Vi; Germany), Ghent University (R; Belgium), Andrei Dorian Gheorghe (Romania), Valentin Grigore (Romania), Marc Gyssens (Belgium), Morton Henderson (Ph; Portugal), Arno Hesse (Germany), Claudia Hinz (France), Wolfgang Hinz (France), Nick James (Israel), Carl Johannink (Spain), Mark Kidger (Spain), Andre Knoefel (Spain), Ralf Koschack (Spain), Detlef Koschny (Spain), Werfried Kuneth (R; Austria), Sylvio Lachmann (Spain), Marco Langbroek & 3 other Dutch Meteor Society observers (France & Spain), Hartwig Luethen (Canary Islands), Michael Maunder (Ph; Bali, Indonesia), Rob McNaught (Ph; Jordan), R B Minton (R; New Mexico, USA), Koen Miskotte (Spain), Sirko Molau (Vi; Spain), Sven Naether (Germany), Mirko Nitschke (Vi; Canary Islands), Sadao Okamoto (R; Japan), Guy Ottewell (South Carolina, USA), Alexei Pace (Malta), Gelu-Claudiu Radu (Romania), Ingo Reimann (R; Germany), Ina Rendtel (Germany), Juergen Rendtel (Vi; Spain), Vanya Rodiger (Croatia), Paul Roggemans (Belgium), Marion Rudolph (Germany), Robin Scagell (Ph; Canary Islands), Ton Schoenmaker (R; Canary Islands), Ulrich Sperberg (Vi; Canary Islands), Umberto Mule' Stagno (Malta), Paul Sutherland (Ph; France), Kiss Szabolcs (R; Hungary), Manuela Trenn (Spain), Mihaela Triglav (Slovenia), Garfield Tsao (R; Taiwan), Jan Van Elst (Belgium), Elfi Vints-Laridon (Ph; Spain), Mark Vints-Laridon (Spain), Roland Winkler (Canary Islands), Nikolai Wuensche (Germany), Ilkka Yrjola (R; Finland), Joseph Zammit (Malta), Wim T Zanstra (R; Netherlands).
Additional thanks go to Chris Steyaert, who provided copies of many of the radio observations in Radio Meteor Observation Bulletins 76 and 77 (December 1999 and January 2000 respectively), and Ina Rendtel, who provided much of the Arbeitskreis Meteore (AKM) observers' data from their group's journal Meteoros vol.2, no.12 (1999).
Disappointingly for many observers in the southern half of England especially, the clearer skies promised in all the national TV and radio weather forecasts for at least part of the post-midnight period on November 17-18 failed to materialise. Instead frontal clouds and rain or drizzle were all that could be seen. Typically, with most national media based in south-east England, this rapidly translated into reports of "Britain misses meteor display" (Times, 1999 November 19).
Fortunately this was not the case across the entire country. The map alongside here shows the distribution of UK observers' sites on November 17-18 (multiple observers or those at very nearby sites are generally indicated by only a single symbol), which gives a very clear indication of where the best weather conditions were: across northern England and south-central Scotland. The partly clear site marked with a question mark on the north coast of East Anglia represents a positive report forwarded only from media sources. The observer(s) have not proved otherwise traceable regrettably, so the sky conditions there are unknown.
Most of the "late clearance" symbols indicate that skies improved enough for some observing only after the Leonid storm had passed, generally after 03:00- 03:30 UT, except for that in London, where 9-year old Ami Frydman spotted a lone possible Leonid in a cloud-gap soon after 23:00 UT. The latest clearance was that shown in the cluster of four symbols near Manchester, after 05:30 UT, caught by the perseverance of observer Ian Rigney. The "late clearance" symbol a little way south of this cluster was from a site in the Pennine Hills where clouds thinned enough to allow several observers with Chris Hall to see some meteors in the post-storm phase, as well as several bright flashes in the clouds from unseen meteors. The one "late clearance" symbol in Northern Ireland was a group from Armagh Observatory with Mark Bailey, who endured overcast skies and drizzle nearly all night, but reported three distinct flashes in the cloud-sheet at about 02:10 UT, 02:30 UT and 02:45 UT. The 02:30 event was bright enough to be seen by the whole group. Similar flashes in clouds were reported by observers at other sites with partly clear skies in northern England and Scotland. Occasionally, some part of the meteor's trail was also seen, as it shot into a patch of clearer sky.
Those who did enjoy better fortune generally found the sky to be overcast for the first half of the night, with any clearer periods coming along only just in time for the storm peak, shortly before 02h UT. Even so, clouds were always a problem, and conditions were often very variable only a few kilometres apart as well. There is no consistent pattern in the better observing times between four separate groups watching from different parts of Edinburgh for example, yet the greatest distance between any was ~7km. Further north in Dundee, Keith Edwards enjoyed the storm in patchy skies but a colleague living on the opposite side of the city saw only clouds all night!
These conditions hampered attempts to compute ZHRs from UK data, though it was clear to all who could observe then that the very highest Leonid rates were seen between ~02:00-02:15 UT, bracketed by a period lasting from about 01:50-02:40 UT when rates were still exceptionally good. Distinctly lower numbers were found beyond these times. Observed rates at best (bearing in mind field-of-view cloud cover percentages never less than ~40-70%) were ~6-8 Leonids a minute, with several observers reporting 3-5 Leonids appearing almost simultaneously in even small cloud gaps on occasion.
Few people attempted photography during the storm because of poor skies, and most of those who did were unsuccessful. At Morpeth though, my father Peter McBeath recorded five Leonid trails on just two 8-minute exposures between 02:08-02:25 UT, a particularly pleasant surprise as the shots were taken using 200 ISO colour print film. Most of the trails were faint, but one magnitude -3/-4 event was recorded too.
At Derwent Reservoir, ~40km south-west of Morpeth, Jeff Lashley was observing with a group from Sunderland AS, using his CCD meteor video system. His camera had about a 25 degree field of view, recording stars to about magnitude +4 or +5, and meteors to about magnitude +3. Tests with this system on non-major shower nights have yielded average meteor rates of ~2/hour. In ~2h10m effective time on November 18 between 01:55-04:17 UT, Jeff recorded 43 trails; 40 Leonids, 2 Taurids and a sporadic. Twenty of the Leonids occurred between 01:55-02:21 UT at up to three a minute (02:11 UT). Allowing for the very variable sky conditions, the drop-off in Leonid rates is clear especially after 02:40 UT. A spectacular Leonid fireball, magnitude ~-6/-8, was beautifully caught at 03:49 UT, leaving a persistent train for around two seconds on the video.
Jeff concentrated on the areas around Aur-Tau-Psc and Ori, while at Morpeth our better skies were to the north in UMa and Dra, so by chance we collected sets of trails at almost right-angles to one another. Using the five photo trails and eleven of the better-sky video trails, it was possible to derive an approximate Leonid radiant from the period 02:01-03:55 UT on November 18 at RA = 10h00m, Dec = +21 degrees. This is pleasingly very close to a video radiant derived from 633 video trails at RA = 10h14m, Dec = +21.9 degrees around the same time in AKM data, and is especially impressive considering the very poor sky conditions the British observations were made under.
One frustrating aspect of the 1999 Leonids for southern-UK observers which was also found in some other parts of Europe, was that skies were significantly better on both November 16-17 and 18-19 than 17-18. Godfrey Baldacchino commented that on Malta, November 17-18 was probably the only night in November nothing astronomical could be seen!
As usual, the early winter weather in Europe produced problems for everyone. In the north, Belgian skies were patchy, though those reporting from there saw part of the storm. In Germany, Ina Rendtel and Marion Rudolph drove 200km west of Potsdam seeking better skies, but managed barely 35 minutes observing between them. In Romania, Gelu-Claudiu Radu drove over 400km in total overnight, being rewarded with one brief gap only soon after 02h UT, even then seeing 10 Leonids in 4 seconds! Elsewhere in Romania conditions were worse, but Andrei Dorian Gheorghe in Bucharest spotted a few flashes probably from bright meteors in a generally overcast sky. For both Vanya Rodiger in Croatia and Mihaela Triglav in Slovenia snow was the problem, blocking the roads and preventing access even to hunt for better skies.
Those north Europeans who decided they wanted the chance to see the Leonid storm under good skies never planned on staying at home anyway, and most had sensibly opted for sites in the Near East, North Africa or the Canary Islands well ahead of time, with the southern parts of Portugal, Spain and France often chosen as good compromise alternatives. Those who were able to take advantage of late weather news were often able to get cheap flights to southern Spain especially, where the forecast better skies did appear. From such places, the storm was a wondrous sight, with single-minute visual counts reported to us in the range of 40-75 Leonids nearest the storm's height. Drawing on all available SPAMS data, the graph above here shows average Leonid ZHRs derived across the storm peak (note the ZHR axis has a logarithmic scale so the lower non-storm ZHRs do not disappear). The highest mean ZHR in our results was ~3370 plus-or-minus 140 around 02:05 UT, a timing the radio data confirms.
Naturally, the IMO's preliminary analysis (reported in the December 1999 issue of the journal WGN) shows far more detail, as it was based on 277,172 meteors, and is illustrated to the right. The SPAMS Leonid total was 24,409 for contrast. Again, the ZHR graph axis is logarithmic, while the time axis is given in degrees of solar longitude, not dates and hours. Solar longitude 234 degrees = November 16d 19h 30m; solar longitude 237 degrees = November 19d 18h 45m. The mean storm peak ZHR based on 2.8-minute intervals was 3700 plus-or-minus 100 at 02:02 UT on November 18. A remarkable feature is the clear secondary peak around solar longitude 235.87 degrees (November 18d 16h), when ZHRs surged as seen from the Far East to reach ~180 plus-or-minus 20 (though the actual value is based on only a few reports and is not certain). The reasons for this unexpected event are still under investigation.
During the actual storm peak itself, a lot of very fine, short-lived structures were found, and at least six minor sub-maxima were identified in the first IMO report around 01:25 UT, 01:43 UT, 01:50 UT, 02:33 UT, 03:17 UT and 03:29 UT on November 18. The graph to the left demonstrates these (filled small squares) and compares them with raw five-minute radio meteor echo counts (larger open squares), the latter data collected by Kiss Szabolcs in Hungary. The fit between the two graphs is most impressive, the radio data providing independent support for the visual results to short time intervals. The time axis here runs between November 18d 00h 43m UT (solar longitude 235.23 degrees) and 03h 34m UT (solar longitude 235.35 degrees), while both vertical axes are given as linear plots this time.
Leonid ZHRs were clearly much lower at times away from the brief, very strong, storm peak and the secondary maximum, but it is interesting that even so, at ~15-30 they were still around or up to twice the value seen at the shower's very best in years away from the storm returns. North American observers were generally unimpressed by this however. Indeed, some comments made it clear that many had hoped storm rates would manifest over the USA, which led to some disappointment, although no serious predictions suggested a Leonid storm was likely in time to the radiant's nighttime visibility over America. Despite this, observations made away from the storm do suggest rates were occasionally quite variable on short time-scales. Two observers in south Wales on November 18-19, Paul and Neville Saunders, noted casual Leonid rates of almost one per minute between about 04:15-04:30 UT for instance, and some other observers earlier that night found similar, lesser, variations.
The Leonid magnitude distribution during the near-storm phase especially was rather unusual in 1999, with few very bright or very faint events. As this is shown by video and photographic evidence, it is a real effect, not simply because visual observers were overwhelmed by the meteor numbers. Looking at the Leonid percentage magnitude distribution based on better-sky SPAMS data (LM better than or equal to +5.5, cloud cover <30%; 838 Leonids and 267 sporadics) shows a surprising similarity to the sporadics'. The sporadic distribution looks quite normal, but we would typically expect to see the Leonids peaking around magnitudes +2 to +3, not +3 to +4 as here. A very marked cut-off was seen between magnitudes +5 to +6 too.
Poor conditions and the fact that very few people routinely reported trains during the storm thanks to the very high Leonid activity means few reliable train details could be derived. The overall train percentages were 33% for the Leonids and 7% for the November sporadics. There is thus some indication of a possibly weaker showing of Leonid trains consistent with their overall fainter magnitudes in 1999, though this is inconclusive because of the small number of meteors involved (just 121 Leonids and 167 sporadics).
Thanks to the generally poor weather across southern Britain on November 17-18, one of our longest-established observers, George Spalding at Denchworth in Oxfordshire, missed the event completely. He summarized his 1999 Leonid observations as follows: November 16-17 was largely good, though a cloudy gap of at least two hours occurred, reducing the amount I was able to do. I was very disappointed with the rates for this night and thought (erroneously) that it boded badly for the critical night.
I was quite hopeful on November 17 that there would be a clear spine down the middle of the UK, encouraged by pretty favourable weather forecasts, and a beautiful day. However, the clouds from the west came in so rapidly around tea-time that I knew we were doomed. There was then drizzle by midnight. So it was a grave disappointment, especially when I found out on the Web by 6 a.m. of the great events elsewhere.
On November 18-19 I perhaps erred in waiting till moonset before starting to observe, as it clouded up fatally after only half an hour. However, it was evident that activity was pretty low. November 19-20 was again partly clear after moonset, but by then I had lost interest.
However, even clearer skies were no guarantee of seeing part of the storm. At Glengarnock near Ayr in western Scotland, SPA Aurora Section Director Tom McEwan fell asleep from exhaustion shortly before 2 a.m. on November 17-18. It had been overcast up to then, but he was dismayed to find on waking around 6 a.m. that skies had broken shortly after he slept, allowing his friends and colleagues from Ayr AS observing nearby to view the storm.
From the Ayr group, Nick Martin and three other observers spent a frustrating first half of November 17-18 watching clouds either live outdoors or on a monitor showing Meteosat images, as the edge of the cloud-sheet crept nearer to them. Around 02:00 UT, the clouds at last started to fragment, and in even quite small gaps, it was obvious the sky was full of meteors, including a magnitude -6 fireball and another unseen fireball that lit up the sky. Nick commented on seeing a strange effect with a couple of his moderately bright Leonid meteors, where a spark-like object seemed to angle away from the line of flight. Another of the Ayr observers also saw this, and the phenomenon may be similar to apparent jets from several meteors recorded on video by professional meteor astronomer Bob Hawkes during the 1998 Leonid fireball night.
Nick remarked that many of the Leonid trails he saw were green in colour, something echoed by other people, including new SPAMS observer Pamela Foster in Pitlochry, Scotland. Pamela was lucky in managing some watching on both November 16-17 and 17-18, and on the latter night recorded a healthy number of meteors in spite of often very poor skies. She was even able to estimate a storm peak time of between 02:00-02:05 UT from her own observations alone.
At Livingston about 20km west of Edinburgh, Tom Patton had gone to bed under cloudy skies, but happily woke later and described his view of the events on November 17-18 in almost real-time via e-mail. 02:52 UT: Standing in the freezing cold in my dressing gown. Just got up for a cup of tea! Skies clear just now over Livingston. Leonids every few minutes. I'm going to get pneumonia. Great sight!! 03:29 UT: Saw lots of shooting stars over the last 30 minutes moving across the east/south high up and low down. Moving singly or in pairs in different directions and of varying intensity. It's bitterly cold here in Scotland so off to bed with a very large single malt whisky to celebrate!
In Edinburgh itself, Mike Holmes was out watching with a few friends: We went up Blackford Glen in Edinburgh and set up a small fire to ward off the cold. It was 100% cloud cover when we went out there at 12:30 a.m., but we thought we'd try to be optimistic. By 1 a.m. we could see Jupiter and the brighter stars through thin cloud and began to see the occasional meteor. By 1:25 a.m. the haze was thin enough that we could see magnitude +3 stars through it, and we'd started counting meteors. The valley is deep enough that we could only see half the sky, and only the east and above us had cloud thin enough to see through. Half of Leo had risen above the angle of the hill. We could see the Plough above one hillside and Orion above the other. We saw about one meteor per minute up to around 2 a.m., when they ramped up to about five per minute. We saw quite a few doubles and a couple of times saw four at once. When trails were visible these were always quite bright green. By 2:45 a.m. fairly thick cloud had covered the sky again. We'd seen over 330 meteors by our count at that point, which is probably more than I've seen in total from 30 years of trying to watch meteor showers. Quite a night!
Such count numbers were very typical from the cloud-influenced UK. At South Shields east of Newcastle, Eva Hans stood watching outside the door of her home for an hour or so from about 02:00 UT, turning in when the cold grew too much, but not before she had counted 100 Leonids in a mostly cloudy sky. My own count at Morpeth, some 20km north-west of Eva's site was 187 Leonids in 1.27h between 01:55-04:25 UT, as a further instance (LM ~+6.1, average cloud cover 55%!).
At Derwent Reservoir on the Durham-Northumberland border, Dave Newton remarked that the problems there were more mist which had lifted into low cloud, but that a clearer area seemed to have formed above the reservoir itself, as if warmer air was rising from the surface of the water, and punching a hole through the clouds specially for the Sunderland AS team. Dave mentioned that Leonid rates started to shoot up rather like turning on a tap after 01:40 UT, but had tailed off before 03:00 UT. Typically, sky conditions were at their best between roughly 03:30-04:30 UT! Even so: There were plenty of bright meteors though, making it a good display despite the weather, although not the storm of fireballs I had hoped for.
In Mechelen, Belgium one of the original prime movers who set up the IMO, and its first Secretary-General Paul Roggemans, was delighted with what was visible there of the Leonid storm, despite again unhelpful skies, with a poor limiting magnitude and a lot of clouds. Paul still managed to spot 99 Leonids between 02:02-02:19 UT, and noted that these were: The best rates I have ever seen under such poor sky conditions!
On Malta in the central Mediterranean, normally noted for its fine, dry weather, Martin Galea de Giovanni reported that two teams of watchers, one at the northernmost point of Malta, the other at the southernmost, spent an almost fruitless night watching clouds. The two groups maintained contact by radio: but the only use of this was that the team from the north managed to warn the south of more showers (RAIN)! The northern group did eventually manage to spot five meteors when the clouds thinned momentarily, but the southern team spotted just a single meteor all night.
The western and eastern ends of the Mediterranean were favoured with better skies, so Spain and Portugal provided some of the best views from Europe. Steve Evans and his colleague Andrew Elliott were in the Algarve of southern Portugal, having struggled with careful handling and customs bureaucracy to get all their photographic and video equipment safely from Britain intact. Sky conditions for the Leonid storm were indeed excellent, and a mass of valuable data was collected, but Steve said afterwards: My only regret is that I was so intent on making sure the equipment was working correctly that I did not have time just to look at the sky and enjoy the show, but even so the display was truly impressive.
In southern Spain, not far from Alicante, Marco Langbroek and several other observers from the Dutch Meteor Society had set up their observing camp on November 17-18. Marco described the night as being quite surreal during the storm, with four visual observers all chanting "yes, yes, yes" simultaneously into their tape recorders as each fresh Leonid appeared. He commented too that all four were mentally and physically exhausted afterwards, a psychological impact that nobody had expected beforehand. He also found he over-reacted to quite ordinary demands during the storm's height, panicking when having to change his tape and not being able to think clearly enough to do it with normal efficiency.
Across the Strait of Gibraltar in Morocco, our man in Marrakesh Stan Armstrong had a similar experience of people calling out in unison on seeing every new meteor. Stan and part of a group of Australian visitors decided to use the sixth floor roof of their hotel as their observing platform for the storm, a stable location for his regrettably unsuccessful photography, but with excellently clear skies for more than three hours from local midnight till after 3 a.m. The limiting magnitude was affected by streetlights and was only about +4.5 at best, but with rates of around 15 Leonids a minute at times, nobody was complaining.
Further south off the north-west African coast, a number of European observers had made for the Canary Islands. Later reports suggested those on La Palma had mostly been stuck beneath clouds, but those on neighbouring Tenerife had seen the storm well. Maggie Daly and SPA Vice President Robin Scagell had travelled with a group of Britons to Tenerife, and there met up with some of the German AKM observers as well as a couple from the USA, the lady of whom was called "Leonid", having been born near the time of the storm in 1966. Both Maggie and Robin carried out photographic observations, but took plenty of time to visually enjoy the spectacle as well, though Robin later commented of his photos: it is a bit unfair that a 7 minute exposure made as the meteors were at their maximum did not record any at all!
Of course, no round-up of recollections like this would be complete without some comments from the Near East, where the Leonid radiant was at its highest before dawn twilight at the storm's maximum. Rob McNaught had headed off to Jordan with his colleague David Asher to witness the storm, and there observed alongside members of the Jordanian Astronomical Society (JAS) led by Mohammed Odeh. It was most appropriate Rob should choose to observe with a JAS group, as he was a former Director of the JAS (though here the acronym stands for Junior Astronomical Society) Meteor Section, now the SPA Meteor Section, back in the late 1970s. The view from Jordan was superb, as expected, but Rob commented there were a great many journalists present as well as meteor observers, and this sometimes created problems. He drew particular attention to a German journalist, who decided he could wait no longer to send his story back to his newspaper, and so he drove off with his car headlights blazing just as the storm was reaching its peak around 02:00 UT, amid the loud complaints of the dark-adapted meteor watchers!
Rob was also able to clear up one small mystery. Many UK evening newspapers on November 18 and the morning papers next day carried a photograph supposedly showing Leonid meteors raining down over the Jordanian desert, but as David Frydman and others in the following days said, the photos were simply of star trails in a quite bright sky, with no meteors visible at all. The answer was simple. Rob had noticed a number of journalists with the JAS group taking some time-exposure photos of the night sky soon after dark, but before moonset. These had been taken up by the various press agencies and passed on as supposedly showing the Leonid storm, which had really happened only hours later!
A huge THANK YOU is as ever due to everyone who contributed data or comments, whether casual reports of impressions, single bright meteor sightings, fully detailed observations or notes on a night spent fruitlessly watching clouds. Well done to all!
One especially fascinating aspect of the 1999 Leonids was the observation by CCD video of six flashes caused by possible Leonid meteorite impacts onto the unilluminated part of the Moon's disc on November 17-18. Several American observers reported these, and a further sighting of other potential impact flashes made visually through a large telescope has recently been announced. The video events were all recorded by at least two independent observers, so the reality of the phenomenon seems assured. Magnitudes were estimated as about +3 to +7 on the video. It is unlikely any craters produced will be visible from Earth, though the debate about the sizes and masses of the impacting objects remains under discussion. David Dunham in the USA has done a lot of work on collecting these reports, and has published further details, including images, on a Website at: http://iota.jhuapl.edu
Following on from some theoretical work based on models of the Leonid meteoroid stream, David Asher calculated that at the time the impact flashes were reported (between about 02:15-05:16 UT on November 18), the Moon was undergoing an encounter with the Leonid stream comparable to what the Earth did in 1833 and 1966, the two greatest Leonid storms ever witnessed in recorded human history! These observations may have wider implications however, as further video observations revealed a small number of possible impact flashes around the time of the Geminid peak in 1999 December as well.
Many people have assumed in the past that the Leonids produce only one storm each time their parent comet Tempel-Tuttle returns to perihelion. Recent investigations of historical reports on the shower suggest this may not be true, and storms could occur in other years near the comet's return as well. Rob McNaught and David Asher suggested in several papers in 1999 that Leonid storms might continue until 2002. Their work must be taken seriously as they managed the amazing feat of predicting the time of the 1999 Leonid storm peak to within a matter of minutes! Their estimated ZHR of ~1500 for the 1999 event was less than half the observed value, but they suggested 2001 or 2002 may produce ZHRs in the 10,000-35,000 class. Their predictions for 2000 are less optimistic, with two possible maximum times around November 18, 03:44 UT and 07:51 UT, perhaps giving ZHRs between ~100-5000. Other theoretical work by Peter Brown indicates highest activity may occur when the Earth passes closest to the comet's orbit on November 17 around 08h UT. Very recently, Ignacio Vasquez indicated the peak ZHRs in 2000 might be of the order ~5,000-20,000, using a method that predicted the 1999 ZHR quite accurately at ~3500 r1000. The level of uncertainty means all observers would be advised to watch for as much of the night on November 16-17 and 17-18 as possible, but 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, and it is possible unexpected events may await detection from the shower, even though most of the predicted peak times are not very favourable for European watchers this year. The Moon is decidedly unhelpful too, as it is at last quarter on November 18, so will be visible in Cnc-Leo all the time the Leonid radiant is on both November 16-17 and 17-18, concealing the fainter meteors; indeed it passes only 3 degrees NNE of Regulus in Leo on November 18-19. In spite of this, good luck and clear skies!
We here reproduce the notes first issued in 1998 as a special SPAMS information sheet, just in case the Leonids do produce something exciting in 2000.
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 60 degrees to 80 degrees 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).
For those interested in learning more about the Leonids, the following is a selection of useful papers and articles on the shower published since our previous Leonid Special Report. Brief notes are given only where the title was not felt to be descriptive enough.
Time now for a final round of thanks to all 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!
Alastair McBeath, Morpeth, 2000 March.