The meteoric event of 1999 was unquestionably the superb Leonid storm on November 17-18, which was even seen from the luckier, less cloudy, parts of Britain. As in 1998, so many reports came in on the 1999 Leonids that we published a Special Report on the shower back in the spring of 2000. Copies are still available if you haven’t got yours yet; please send our Assistant Director Shelagh Godwin an A5 SAE with your request (her address is on page 8). Away from the Leonids, patchy skies were prevalent throughout the year, and many of the moonless showers received less visual coverage than we might have liked because of poor conditions. Fortunately, useful radio results were made for most of these periods, but there were also some interesting events non-instrumental observers could follow too, as we shall see. I must apologise for the lateness of this Review which would normally have been published in the spring. A number of factors have contributed to this, including the large amount of Leonid data and my still on-going illness. Thank you for your patience, and of course for all your observations during last year.
Grand Totals and Observers
The overall totals for the various observing techniques were: Visual – 1451.8 hours, 42,358 meteors; Photographic – 1550 hours, 115 trails (of which 70 have so far been identified; these included 69 Leonids and 1 sporadic); Radio – 45,388.9 hours; Video – 1004.6 hours, 6584 trails (including 725 Leonids, 485 Perseids, 484 Taurids, 387 Orionids, 123 delta-Aquarids, 114 Geminids, 85 kappa-Cygnids, and 3663 sporadics). The visual, photographic and video tallies were especially boosted by data from the German Arbeitskreis Meteore (AKM) observers, details of which were taken from the AKM’s journal Meteoros kindly provided by Ina Rendtel. Especially active AKM observers included Juergen Rendtel and Sven Naether (both with just over 200 hours of visual observing each for the year), Rainer Arlt, Frank Enzlein, Christoph Gerber, Andre Knoefel, Sirko Molau, Harald Seifert and Oliver Wusk, who each carried out over 40 hours of visual watches. Most of the radio data came from the Radio Meteor Observation Bulletins (RMOBs), which Chris Steyaert in Belgium thoughtfuly submitted to us via e-mail. Reports, ideas, suggestions and comments have come from other observing and non-observing Section correspondents too, which have all helped complete the picture of meteor activity built up over the year as presented in the regular SPA News Circular columns, the SPAMS results articles published in the International Meteor Organization’s (IMO’s) journal WGN, our Special Leonid Report and this Review. All contributions are most gratefully acknowledged. The list of people providing observational data at times outside those covered by our Special Leonid Report follows. Every one is to be congratulated and thanked for their time and trouble in observing and submitting their data, without which the Section could not continue to function. The listing contains the country most observations were made from, with abbreviations indicating the type of observing carried out. “P” denotes photographic, “R” radio, “Vi” video, and “V” that visual results were also contributed by that person. Observers without an additional letter provided purely visual data:
Enric Fraile Algeciras (RMOB, Spain; R), members of the AKM (Germany; P/Vi/V), Stan Armstrong (England), members of the Astronomical Society of South Africa, Mike Boschat (RMOB, Canada; R), Jay Brausch (USA), Eisse Pieter Bus (RMOB, Netherlands; R), Michael Ching (Portugal), D Choudray (England), Paul Coleman (Turkey), Mary Cook (England), Tim Cooper (South Africa), Andrea Csiki (Romania), Maurice de Meyere (RMOB, Belgium; R), Steve Evans (England; Vi), Bev Ewen-Smith (Portugal; R), Ghent University (RMOB, Belgium; R), Shelagh Godwin (England), Chris Hall (England), Alan Heath (Turkey; P/V), Morton Henderson (Scotland; P/V), Ou Yang Tian Jing (RMOB, China; R), Will Kelsey (RMOB, USA; R), Werfried Kuneth (RMOB, Austria; R), Marco Langbroek (Netherlands), members of Malta AS, Tony Markham (England), Michael Maunder (England), Alastair McBeath (England), Tom McEwan (Scotland), R B Minton (USA; R), Sadao Okamoto (RMOB, Japan; R), Ivor Paul (South Africa), Trevor Pendleton (England), Graham Pointer (Scotland), Ian Rigney (England), Ton Schoenmaker (RMOB, Netherlands; R), Chikara Shimoda (RMOB, Japan; R), Auke Slotegraaf (South Africa), Adrian Sonka (Romania), George Spalding (England), Pierre Terrier (RMOB, France; R), Garfield Tsao (RMOB, Taiwan; R), Laura Unci (Romania), Robert S White (England; R), Ilkka Yrjola (RMOB, Finland; R), Wim T Zanstra (RMOB, Netherlands; R).
The leading UK visual observers managed between 20-35 hours of watching each during the year, giving some indication of the poorer conditions mentioned above (several people in Britain put in between 30-70 hours in 1998, for contrast). Those hunting for better skies overseas usually managed more, around 30-50 hours typically, but watchers everywhere struggled to reach even 5-15 hours. With many UK residents heading abroad seeking clearer skies to view mid-August’s solar eclipse, take in the Perseids or see the Leonids, only a few hours of observing at the appropriate time – sometimes even from the UK! – was more than enough to make for some very satisfied observers even so. In addition five of the radio observers operated on more than 250 days during the year.
Highlights of the Year
Quadrantids: (See also News Circular 208 and our results article in WGN 27:6 (1999 December), pp. 333-335) While weather and Moon conspired to wreck a visual view of the Quadrantids, radio observations revealed the highest echo counts occurred between 23-01h UT on January 3-4, much as expected. This mean peak’s centre was about an hour later than predicted, but the uncertainty in the radio data, plus the fact that no visual results were available for confirmation, means this minor discrepancy cannot be taken particularly seriously.
Plotted Virginid Radiants: (See also News Circular 209 and our results article in WGN 28:1 (2000 February), pp. 37-40) As in 1998, Tim Cooper in South Africa was again our chief Virginid meteor plotter during the early-year project. Two weak possible radiants were detected by Tim’s efforts in March, around RA 11h15m, Dec -5 degrees from March 8-10, and near RA 11h50m, Dec -9 degrees on March 18-19. These may represent the drift of a single radiant during the intervening ten days, as their spacing is what we would expect to see if so, but neither position exactly matched any radiants found in our five-year Virginid plotting project from 1988-1992. However, the first radiant lay only about 5-6 degrees south of the southern boundary of Area 6 (centred on RA ~11h10m, Dec ~+10 degrees, but extending south to Dec -2 degrees, active in early March), while the second was a few degrees north-west of the north-western tip of Area 2 (centred near RA ~12h15m, Dec -15 degrees, active in mid-March). Between April 13-19 Tim found two more weak, diffuse, possible radiants around RA 13h35m, Dec -4 degrees and RA 13h05m, Dec 0 degrees. The first of these was close to our earlier Area 10 (centred on RA 13h45m, Dec -3 degrees in mid-late April), while the second was about midway between Areas 10 and 9 (Area 9 active in mid April, centred close to RA 12h30m, Dec +3 degrees). Of course, these and other suspected radiants need many more plotted Virginid meteors to confirm or deny their existence, so send an A5 SAE to Shelagh for your meteor plotting pack if you have not yet done so (which includes details on our late-year Aurigid and Taurid plotting project too).
Gamma Normids: (See also our results article in WGN 28:1 (2000 February), pp. 37-40) This shower does not feature in our “Meteor Showers List” as its radiant (at RA 16h36m, Dec -51 degrees on March 13) is too far south to be seen from Northern Europe. Any meteor observers travelling to the southern hemisphere in late February to late March should be aware of it though, since low rates of swift meteors are quite possible, especially near its suspected maximum on March 13 (peak ZHR ~8). In 1999, four independent observers, two each in South Africa and Australia, reported observed rates to us of up to 2-3 gamma-Normids per hour between March 11-21. The highest rates were seen on March 17, when ZHRs were ~6 +/- 3. Although the rates may not sound too exciting, this represents one of the very few definite sightings of this shower made in the last 15 years, and suggests the “known” maximum time may be incorrect now.
Lyrids: (See also News Circular 209 and our results article in WGN 28:1 (2000 February), pp. 37-40) The UK missed out during this shower in 1999 thanks to poor weather, but preliminary IMO analyses indicated ZHRs of ~20 +/- 8 overnight from Europe on both April 21-22 and 22-23. Higher rates (ZHRs perhaps ~30 +/- 10) were suspected on April 22-23, when only two observers’ data were available to check, so they remain very uncertain. Radio reports showed almost comparable activity on both nights, but most favoured a single maximum for the Lyrids on April 22-23. Unfortunately there are few radio datasets available either. The expected peak should have fallen around 16h UT on April 22.
Eta Aquarids: (See also News Circular 209 and our results article in WGN 28:2/3 (2000 April-June), pp. 81-84) Tim Cooper was once more our leading visual observer for this shower, struggling with their short pre-dawn observing window even from South Africa in early May, as well as a waning gibbous Moon. The ZHRs he saw were between 45-70 +/- 10-15 on May 2-3, 3-4 and 9-10, while the radio results also indicated fairly uniform rates from about May 3-12 in some cases, without an obvious single, sharper maximum. May 4-5 produced the most consistent radio peak in the majority of datasets, though half the radio observations showed another peak as strongly on May 8, with a further spike in long-duration echoes (generally assumed to be due to brighter meteors) found on May 10. This is consistent with some of the variability found from the h Aquarids in 1986-95 results in an analysis by Tim Cooper, and shows the source to be well worth watching for those at suitable locations.
May-July Daytime Radio Shower Activity: (See also “Daytime Taurid Complex Stream Activities, May-July 1999: A Provisional Report”, A. McBeath, WGN 28:1 (2000 February), pp. 21-29) In 1993, professional meteor astronomer David Asher, now at Armagh Observatory, Northern Ireland, suggested the complex of Taurid meteor streams seemed to have a recurrent “swarm” within them which had produced occasional unusual events, most obviously heightened rates of bright meteors for the October-November Taurid showers, but also a cluster of meteorite impacts on the Moon in 1975 June. He gave possible future dates for this “swarm” to reappear, including October-November 1998, a time when SPAMS and IMO observations revealed heightened Taurid rates with more shower fireballs than usual. Another highlighted time was during the Taurids’ daytime return in 1999 June, from the zeta-Perseids (which usually peak around June 9) and the beta-Taurids (peak within a few days of June 28). As a result, I examined radio and visual meteor data, along with reports of unusual noctilucent cloud sightings and the radio propagation mode Sporadic-E, from late May to mid July 1999 searching for signs of this potential “swarm” recurrence. Unfortunately, largely thanks to signal interference with the radio results, the findings of this investigation were inconclusive. The Arietid (about June 6-7), zeta-Perseid and beta-Taurid maxima were all recovered, and slightly anomalous radio activity was found on June 13-17, 20-21 (followed by a very curious deep-southwards penetration of noctilucent clouds over Europe and especially North America on June 22-23), 27-28, July 1-2, 5-8 (again with a possible far-southern expansion of noctilucent clouds over North America) and July 11 between at least 13:00-13:45 UT. The noctilucent cloud sightings are important because the clouds may form around meteoric dust or charged particles, and Sporadic-E sheets may be formed around similar material.
June Lyrids: (See also our results article in WGN 28:2/3 (2000 April-June), pp. 81-84) This minor shower was first detected in 1966, but seemed to have vanished by the late 1970s, until several independent observers suggested weak rates had been seen in 1996 June. Regular observers with dark June skies were alerted to check for any shower activity in the moonless conditions of 1999. The June Lyrids were previously found active between June 11-21, with a maximum on June 16 when ZHRs might reach 5, from a radiant at RA 18h32m, Dec +35 degrees. Past June Lyrids were of slow-medium speed and typically faint. Despite considerable efforts, no genuine trace of June Lyrid activity was found in SPAMS or IMO data, though the time is one to watch in future just in case the shower may revive once more.
June Bootids: (See also News Circular 209 and our results article in WGN 28:2/3 (2000 April-June), pp. 81-84 for the 1999 lack-of event; “The June Bootids – Past and Present Records”, R. Arlt, IMC Proceedings 1998, Star! Lesn!, IMO, 1999, pp. 29-42, has an in-depth examination of the 1998 event, and all past recorded returns of the shower; “Surprising Comeback of the June Bootid Meteor Shower”, R. W. Sinnott, Sky & Telescope 99:6 (2000 June), pp. 100-104, is a review of the 1998 shower based on IMO and Japanese radio data; “The Analysis of a Weak Meteor Shower: The June Bootids in 2000”, R. Arlt, WGN 28:4 (2000 August), pp. 98-108, analyses the very low possible to nonexistent June Bootid rates seen in 2000 June, including a detailed technical discussion of the problems of visual observations of very weak meteor showers generally) After the unexpected June Bootid return on 1998 June 27-28, even strong moonlight wasn’t enough to stop observers checking for activity from this source once again in 1999, but no trace was found in either our visual or radio results. On a global visual scale, IMO data revealed no sign of June Bootids either. As with the June Lyrids though, still a period to check in future.
July 7 Superbolide over New Zealand: (See also News Circular 212 and “Daytime Taurid Complex Stream Activities, May-July 1999: A Provisional Report”, A. McBeath, WGN 28:1 (2000 February), pp. 21-29) This brilliant daylight fireball occurred at 04:14:42 UT on July 7, confirmed by American Department of Defense satellite reports and visual observations made widely across both main islands of New Zealand. The object’s near-terminal explosion at about 37 km altitude above North Island shook buildings and the ground, and produced thunder like re-echoings for almost a minute afterwards. No meteorites were recovered, hardly surprising as the roughly east-west trajectory would have dropped any solid objects into the sea.
Pegasids: (See also News Circular 212 and our results article in WGN 28:2/3 (2000 April-June), pp. 84-87) For once this minor shower did not disappear into the clouds, and enough data reached us to allow the maximum on July 10-11 to be established, although ZHRs were only about 4 +/- 3 even then. The swift-moving meteors are fairly unmistakable for twilight-braving UK watchers at least.
July 31 Fireball over the Southern North Sea and the Low Countries: (See also News Circular 212 and our results article in WGN 28:2/3 (2000 April-June), pp. 84-87) At 20:57 UT, a magnitude -8 or brighter fireball was spotted in evening twilight from various locations across Belgium and the Netherlands. Observations revealed the meteor had had a grazing trajectory just touching the meteor layer in the upper atmosphere, as its end height was still about 60-70 km, much higher than such a bright fireball would normally finish. The surface track ran from a point over the North Sea some 75 km north-west of Amsterdam to near the Dutch-Belgian border roughly 15 km south of Eindhoven. The event should have been visible from parts of south-east England at least, but no reports were received despite appeals in various places afterwards.
Perseids: (See also News Circulars 210 & 212 and our results article in WGN 28:2/3 (2000 April-June), pp. 84-87; for full details on the 1998 return see “Global Analysis of the 1998 Perseid Meteor Shower”, R. Arlt, WGN 27:5 (1999 October), pp. 237-249, including an examination of the particular problems bright moonlight poses for establishing accurate limiting magnitudes; our results article in WGN 27:2 (1999 April), pp. 135-139 has further news of SPAMS 1998 Perseid observations; “First Results of the 1999 Perseid Meteor Shower”, J. Rendtel & R. Arlt, WGN 27:5 (1999 October), pp. 250-255 has an initial report based on global observations from 1999) The poor weather that hit south-west England’s view of the solar eclipse on August 11 spread across the UK until after the Perseid maximum on August 12-13, but as the graph alongside illustrates, enough data were available from all our observers, UK and overseas, to derive mean Perseid ZHRs for almost every night in August until 16-17. The highest mean ZHR was 98 +/- 9 for the period 00:00-01:00 UT on August 12-13. The more detailed IMO results showed a first maximum almost exactly as expected at 23:05 UT on August 12, when ZHRs were 104 +/- 4. The secondary or “traditional” maximum followed at ~01:35 UT on August 13 (ZHR = 87 +/- 6), with the new tertiary peak, first seen in 1997, coming along at about 09:50 UT on August 13 (ZHR = 80 +/- 4). All these peaks were lower than has been seen for most of the last decade, and it is clear the new primary maximum first found in 1988 is now beginning to blend into the secondary peak, much as predicted. In SPAMS data, the Perseids’ corrected mean magnitude was +2.5 while the August sporadics’ value was +3.5, with 36% of Perseids and 2% of sporadics leaving persistent trains.
Delta Aurigids: (See also our results article in WGN 28:4 (2000 August), pp. 125-130) Though full Moon saw off attempts to cover the alpha-Aurigids in late August and early September, at the start of our annual autumnal meteor plotting project, the delta-Aurigid peak expected around September 9 was much better-placed. However, despite quite reasonable coverage (though sadly with all-too few possible shower meteors plotted), no clear maximum from this source was found in 1999, either in visual or radio results. Why this should be is unknown, and it indicates the need for more observations in future years.
New September 17 Radio Peak: (See also our results article in WGN 28:4 (2000 August), pp. 125-130) European radio operators recorded a small, previously undetected, echo-count peak on September 17. A possible radiant in Orion-Gemini was suspected from radio observations on 1989 September 16, which may be related. The timing of the 1989 event was equivalent to 22-23h UT on 1999 September 16, which time produced nothing especially unusual in radio reports. Instead, the 1999 September 17 rates seemed highest between roughly 05-13h UT. This timing could confirm the approximate radiant area, since such a radiant would be above the horizon between about 23-14h local time daily in mid September. The source could be an outlying part of the Aurigid showers, though nothing has yet been recorded from near Orion-Gemini by our visual meteor plotters at this time.
Sextantids: (See also News Circular 213 and our results article in WGN 28:4 (2000 August), pp. 125-130) This daytime radio shower produced an unexpectedly strong return on September 30, an echo-count peak which dominated the rest of September’s moderate radio activity, something not normally seen, albeit it was only about two-thirds as strong as the Orionid radio maximum three weeks later. Suspicions of a 4-5 year periodicity in more active Sextantid returns have been voiced, though the last comparably strong radio peaks at this time were detected in 1988-89. Others may have been missed. Occasional visual meteors from this source can be spotted only by near-equator observers an hour or two before sunrise, as the radiant rises at the start of morning twilight for British watchers.
Draconids: (See also News Circular 213 and our results article in WGN 28:4 (2000 August), pp. 125-130 for brief details on the 1999 event; the 1998 outburst was discussed further by several articles in WGN 27:3/4 (1999 June-August), including our own September-October results paper in this issue on pp. 209-214) Contrary to negative expectations following the 1998 outburst, based on past observations that normally only a single return of the Draconids is likely to happen near the perihelion passage of the shower’s parent comet 21P/Giacobini-Zinner (which occurred last in 1998 November), ZHRs of perhaps 10-20 +/- 6-8 were reported from this source between 09-12h UT on 1999 October 9. Visual and radio observers from Japan detected the outburst particularly clearly, though only one European radio system could confirm the timing properly. Low visual Draconid rates were suspected from Japan and Europe on October 8-9. However these were not confirmed by radio results, and about equal numbers of visual observers reported seeing a few or no Draconids during their October 8-9 watches. The evidence for such earlier activity is thus highly inconclusive. Why this weak outburst happened, and why it occurred about 15 hours later than the equivalent time for the 1998 event, remain unknown. The shower’s place on our annually-reviewed “Meteor Showers List” seems more than justified, flagging this period as another time to watch in the coming years. Orionids: (See also News Circular 213 and our results article in WGN 28:4 (2000 August), pp. 125-130) October’s waxing gibbous Moon created problems for visual observers of the Orionids. Even so SPAMS ZHRs were computed for every night between October 11-12 and 20-21 (except October 13-14), and were typically around 5-8 +/- 3-4 until October 19-20 (ZHR = 16 +/- 2). They were still rising the following night (ZHR = 23 +/- 5), after which the Moon and clouds intervened. Radio results showed a maximum on October 22, as predicted, that appeared unexceptional. There was no sign of the enhanced activity sometimes found around October 17-18, last seen in 1998. Corrected mean magnitudes for the Orionids and October sporadics respectively were +3.0 and +3.6, with 32% of Orionids trained.
Taurids: Too few Taurids were plotted during our autumn project for a detailed analysis unfortunately. Most nights between November 2-3 and 16-17 did allow some observations, with low Taurid ZHRs throughout. Northern Taurids seemed more prevalent on November 2-3 and 8-9, the Southern Taurids more obvious around November 6-7 and 9-10, but the difference was marginal. The highest combined Taurid ZHRs, ~9-12 +/- 5-6, were found on November 2-3 and 8-9 to 9-10. Radio and scant visual data in late October showed no trace of the higher Taurid activity seen then in 1998. From October-November observations, corrected mean magnitudes for the Southern and Northern Taurids were +3.5 and +3.1 respectively, with the November sporadics’ value derived as +3.3. The train proportions for these three sources in order were: 6%, 3% and 6%. Possible Gamma Ursae Majorids: (See also News Circular 213, notices posted to the IMO-News e-mailing list between October 20 and November 11 (see Website: http://www.imo.net for these archives), and on the SPA Website http://www.popastro.com) Alerts were issued by e-mail to regular observers across the world after news broke that Comet C/1999 J3 LINEAR might produce swift-meteor activity from a radiant near gamma Ursae Majoris around November 11. Despite careful monitoring by numerous observers, SPAMS watchers among them, no genuine visual activity was noted from this source. The professional meteor radar system at Ondrejov in the Czech Republic found enhanced rates perhaps from this radiant between 21-03h UT on November 11-12, though no unusual radio reports coincided with this time. The gamma-Ursae Majorid meteors may thus have been very faint (most radar meteors are too faint to be observed by normal visual techniques or by typical radio meteor systems).
Leonids: (See also News Circulars 210 & 213, our special Leonid results articles in WGN 28:2/3 (2000 April-June), pp. 64-69 (radio), pp. 69-76 (visual and imaging) and WGN 28:4 (2000 August), pp. 113-117 (personal recollections) for reports on the SPAMS’ view of the 1999 Leonid storm; also send for your copy of our Special Leonid Report which has further details and references on the shower. Other Leonid articles published since our Special Report came out include: “17/18 November 1999: The Night of the Leonids”, R. Jehn, M. Landgraf, W. Flury, I. Harrison, D. Koschny & J. Zender, ESA Bulletin 101 (2000 February), pp. 114-115 (very early report with an inflated peak ZHR of ~5000); “Looking Back, Looking Ahead: Will The Leonid Storms Continue?”, J. Rao, Sky & Telescope 99:6 (2000 June), pp. 30-37 (review of the storm, including photos, details of the lunar impact flashes and predictions for the coming years); “The Leonids’ Rising Stars”, D. Fischer, Sky & Telescope 99:6, p. 38-40 (an interview with David Asher and Rob McNaught on their Leonid peak time predictions); “Storm Chasers”, J. K. Beatty, Sky & Telescope 99:6, pp. 42-45 (NASA airborne observations of the Leonid storm); “Catching A Falling Star”, J. D. Drummond, C. S. Gardner & M. C. Kelley, Sky & Telescope 99:6, pp. 46-49 (Lidar observations of Leonid trains in 1998-99 and simultaneous meteor sounds); “Predictions of a fine display of Leonids next week”, M. Bailey (in an RAS meeting report for 12th November 1999), The Observatory 120:1156 (2000 June), pp. 175-177 (summary of predictions for the then-to-come Leonid storm)) The most stunning meteoric event of 1999 receives no extra mention here than these additional references, since our Special Report is larger than this Annual Review!
Meteorite Fall, Ireland, November 28: (See also News Circular 213) A brilliant bolide at 22:10 UT on November 28-29 was seen as magnitude -12 even low in the south-western sky from the Isle of Man. From Co. Carlow, Ireland, the meteor lit up the countryside like daylight, while the explosive blast from the object’s final fragmentation shook houses like a nearby bomb. The town of Carlow, south-west of Dublin, reported especially severe sonic booms, and calculations quickly showed any meteorites should have fallen nearby. Despite this, and the offer of a reward of up to 20,000 pounds for any meteorites recovered, money put up by a private Scottish collector, it was mid December before any objects came to light, recovered near Leighlinbridge, Co. Carlow. By January 2000, four of these objects were definitely confirmed as meteorites, totalling about 271g in weight, and classified as L6 chondrites (low iron content stony meteorites, which had been strongly heated before their encounter with Earth, containing small round inclusions called chondrules. Chondrites are believed to contain some of the most ancient material from the formation of the Solar System). This was the first observed meteorite fall and recovery in the British Isles since the Glatton meteorite in Cambridgeshire in May 1991.
Geminids: (See also News Circular 213, and “First Analysis of Global Data of the 1999 Geminids”, J. Rendtel, WGN 28:1 (2000 February), pp. 19-21) Moonlight favoured the Geminid maximum in December, and observers were out in force despite the winter cold. The graph to the right indicates that visual observing was possible on every night between December 6-7 and 15-16, and shows mean ZHRs for each night. Individual ZHRs were 100+ from after midnight on December 13-14 (mean ZHR for that night was 103 +/- 10) to the first half of December 14-15 in our results, but the highest ZHRs, ~122 +/- 6, were found around 17h UT on December 14 in IMO global data. Radio results showed their highest counts on December 14-15 too, though the difference to meteor echo numbers the previous day was often not great. Corrected mean magnitudes for the Geminids and December sporadics were +2.8 and +3.8 respectively, with 6% of Geminids and 5% of sporadics leaving persistent trains.
As ever, we have given some comparison monthly sporadic data for the better-observed showers of the year as we have gone along, since the sporadics are our essential calibration source for all other meteor activities. Although they can be routinely monitored along with the main showers, it is important we have as much coverage of the sporadic complex during the rest of the year as we can too. This additionally allows coverage of the minor showers, of which at least one or two are active on nearly every night of the year. Based on details from 817 sporadics seen in better skies during 1999, a corrected mean magnitude of +3.4 has been derived, with a train population of 5%.
Surprisingly few fireball reports were received by the Section this year, with just 29 meteors of magnitude -3 or more provided with any details. Most of these were seen from only one site, the main exceptions being those brilliant events detailed above from July and November. Nine fireballs occurred on December 13-14, the UK’s best night during the Geminids.
Radio Meteor Observations
Radio meteor observations have become an important part of the Section’s work in recent years. As it grows clearer that the activity peaks being detected can be reliably confirmed by different systems from year to year at the same time, so confidence increases that radio details alone can provide us with a window into otherwise inaccessible meteor showers, such as those active during the daytime, or those night-time showers that are lost to bright moonlight. Following from this, it is now possible to integrate the radio data more fully into the ordinary reports. There are still difficulties, but it seems most meteor radio set-ups are detecting levels of activity comparable to what the visual observers see, though the echo count numbers are normally higher than the meteors a single visual observer can count. With radio systems, we are able to view a much larger part of the atmospheric meteor region from a single site. In a way, radio is as if a visual watcher had an effective field of view several times larger than our eyes can provide. This is a very simplified idea, if a helpful one, as it reinforces the concept that most radio systems are currently detecting similar meteors to what the visual watchers see. In turn this means if an anomalous night-time radio meteor peak is detected, we should check the visual results for new features too, which gives us a valuable tool to assist our understanding of meteor behaviour generally. Radio results gave the first indication that the Taurids had shown unusual activity in late October 1998, for instance.
Now it is time for me to hand you over to our Assistant Director, this year for some thoughts on apparent meteor velocities, essential for accurate meteor plotting observations.
Meteor Velocities – by Shelagh Godwin
Imagine that you are a child, running through the spray from a garden hose. The spray is going in one direction. When you run along the spray towards its source the drops of water hit you harder, because they seem to be travelling faster towards you. When you run across the spray the drops of water will hit you less hard, because they are travelling more slowly towards you. When you run along the spray away from the source, the drops, moving in the same direction as you are, hit you less hard because, in relation to you, they are travelling more slowly still.
For that carefree child, substitute our Planet Earth. For the spray from the hose substitute a stream of dust particles left behind by a comet or an asteroid, and extending right round its orbital path. The angle at which the Earth approaches this stream will affect the speed at which the dust particles, the meteoroids, enter the Earth’s atmosphere before burning up.
Now imagine you are standing on a tennis court. Pete Sampras serves at 120 miles per hour (190 kilometres per hour). The ball comes straight at you. But because it is coming straight at you the ball seems to be travelling slowly. (If your reactions are too slow and the ball hits you, you will know just how fast it was moving by the bruise it makes afterwards!) If he messes up the serve and the ball passes to one or other side of you, landing out, it will seem to you to have been travelling faster because it was passing across your vision, rather than towards it.
Substitute for the tennis ball coming straight at you a point source or short-pathed meteor. Because it is coming straight at you from its radiant point it will appear to be travelling more slowly. A meteor travelling across your vision at a greater distance from its radiant will have a longer path, and will appear to move faster.
So what does this mean for the observer? It can be very difficult to determine which shower a meteor belonged to simply by trying to establish the radiant by prolonging the path of the meteor back in a dead straight, imaginary, line. In the summer months, there are many radiants close to each other, for example. Plotting does help, but is not usually sufficient. This is why the SPA Meteor Section plotting projects encourage observers to make a note of both the path length and the apparent speed of each plotted meteor on a 0-5 scale, where 0 = stationary (that is, at that meteor’s apparent radiant point), 1 = very slow, 2 = moderately slow, 3 = medium speed, 4 = fast and 5 = very fast. Information of this kind helps us, for instance, to distinguish between an Orionid and a Taurid.
Streams with low-velocity meteors include: the summer alpha-Capricornids (23 km/s), both Taurid showers (27-29 km/s), and the mid-December Ursids (33 km/s).
Streams with high-velocity meteors include: the summer holiday-time Perseids (59 km/s), the Leonids (71 km/s; this is almost as fast as meteors that are still members of the Solar System can move), Orionids and eta-Aquarids (66 km/s for both, as both result from debris from Comet Halley).
Currently, the SPA Meteor Section runs two plotting projects each year, for the Virginids in the opening months of the year, and the Aurigids and Taurids in the autumn. If you would like to join in with these, please send me a large SAE for details (my address is on p. 8).
These notes will be adapted for use in the “Shelagh’s Spot” feature of our regular News Circular columns. We’re always on the look-out for new topics or ideas to cover in these, so if you have some thoughts you’d like to share about meteor observing, or questions to ask, drop Shelagh or me a line with an SAE.
International Meteor Organization News
Again, the IMO has been busy at the forefront of global meteor science this year, with important analyses published on several major showers, as we have noted above. It seems almost incredible that so many people around the world now rely on these publications and other material produced by the Organization to tell them what is happening with the meteor activity the Earth encounters, when only a few years ago many people still clung to the even-then outdated idea that observations by individual local groups in one region or country alone could tell us all we needed to know about meteors, as if the meteors would recognise our ever-changing national boundaries here on Earth! Thankfully, the IMO’s members and its hardworking officers have continued to keep apathy and complacency away, and seem keener now than when the Organization was founded to make meteor observations and compute analyses so we can continue to enjoy an unparallelled overview of what each year’s meteor round has been doing. If you are interested in joining the IMO and helping to participate in this work, contact the Director with an SAE for more information, or see the IMO Website.
A selection of interesting meteoric texts published since our last Annual Review, and not already mentioned.
- “Life’s Far-Flung Raw Materials”, M. P. Bernstein, S. A. Sandford & L. J. Allamandola, Scientific American 281:1 (1999 July), pp. 26-33. An overview of how complex organic molecules necessary for life on Earth may well have originated in a pre-solar molecular cloud, and been carried to Earth on meteors and meteorites.
- “Deep Impact”, M. J. Bailey, Astronomy & Geophysics 40:4 (1999 August), pp. 4.25-4.26. Report of a meeting in Turin from 1999 June 1-4, on surveying near-Earth objects (NEOs) and what warning is possible, or indeed desirable, of an impending impact by one.
- “The Limiting Magnitude Problem”, P. Zimnikoval, WGN 27:3/4 (1999 June-August), pp. 153-163. A new series of limiting magnitude areas to help determine limiting magnitudes worse than +5.5.
- “The Torino Scale: Gauging the Impact Threat”, J. K. Beatty, Sky & Telescope 98:4 (1999 October), pp. 32-33. A new impact event scale suggested for use by the IAU for possibly hazardous NEOs.
- “Calamity at Meteor Crater”, D. A. King, Sky & Telescope 98:5 (1999 November), pp. 48-53. Review of the creation of Arizona’s Meteor Crater, and possible future collisions with similar objects.
- “Fifteen Years of Collecting Observations in the Visual Meteor Database”, R. Arlt, WGN 27:5 (1999 October), pp. 226-235. An overview of the activity reported to the IMO’s central visual meteor database, created by Paul Roggemans in the 1980s.
- “Meteoroids 1998”, edited by W. J. Baggaley & V. Porubcan, Astronomical Institude of the Slovak Academy of Sciences, 1999. A collection of 79 fascinating papers presented at the most recent IAU Commission 22 (Meteors) conference in Slovakia in 1998. Some are very technical, but a must for all serious meteor science enthusiasts.
- “Possible New Radiant in Early February”, J. Rendtel & G. W. Gliba, WGN 28:1 (2000 February), pp. 13-18. Discussion of a possible new
- “xi-Bootid” shower, found in visual data only, and demonstrated by video reports not to be a genuine meteor shower.
- “Meteor Nights”, D. H. Levy, Sky & Telescope, 99:4 (2000 April), pp. 86-87. Personal recollections of mostly casual meteor observations, including the 1999 Leonids and Geminids.
- “Xi Bootid Shower Confirmed”, G. Seronik, Sky & Telescope 99:5 (2000 May), p. 132. A confused piece which claims our item 8 above shows the supposed “xi-Bootid” shower to be real – exactly the opposite of the actual situation!
- “Yukon Meteorite Bonanza”, Sky & Telescope 99:6 (2000 June), p. 22. A brief report on the recovery of a carbonaceous chondrite meteorite following a spectacularly brilliant meteor over north-west Canada on 2000 January 18. Further details on this event are given in the 2000 September S&T (100:3, pp. 18-19), now named the Tagish Lake fireball after the frozen lake surface from which many meteorites were recovered. Further short items on salt in meteorites (p. 19) and a list of new Martian and lunar meteorite finds (p. 21) are in this same issue.
- “Global Electrophonic Fireball Survey”, D. Vinkovic, Z. Andreic, S. Garaj, D. Kovacic, M. Mladinov & G. Zgrablic, WGN 28:2/3 (2000 April-June), pp. 48-53. Meteor simultaneous sound survey announced, complete with a special report form.
I hope I shall manage to get next year’s Annual Review ready earlier than this very delayed one. With that in mind, I will just drop a few reminders here to look out for the Leonids in November (as if I really needed to remind anyone how important covering even this year’s badly moonlit return is!), the Ursids in December, the Quadrantids (peak expected around 12h UT on 2001 January 3; Moon-free after midnight as the radiant is rising higher) and the Lyrids on 2001 April 21-22 (dark skies and a Saturday night maximum; what more could we ask for?). I look forward to hearing of your efforts and seeing your reports. Good luck, and as always, clear skies!
Alastair McBeath, 2000 August 28
Director: Alastair McBeath, (Observations and advice on all aspects of meteor work).
Assistant Director: Shelagh Godwin, (New Section members and Section publications).