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Perseids 2002

Introduction

While the Perseids are always eagerly anticipated as one of the highlights of the year for meteor watchers, new Moon on 2002 August 8, just a few days before the expected peak on August 12-13, raised hopes still more. The maximum was due around 22h30m UT on August 12, just as the radiant would be reaching a usable elevation for British sites, so it was a little disappointing that even the clearer parts of the UK had haze and patchy clouds at times all night on August 12-13. Luckily, observers were generally happy with what they saw despite the conditions, thanks to a pleasing number of bright to fireball-class Perseids about.

Preliminary SPA Perseid reports had appeared on this website and in Electronic News Bulletin 107 by late August, with a first printed update in News Circular 228. Since then, more observations have arrived and additional analyses have been carried out, including a global analysis by Rainer Arlt and Andreas Buchmann of the International Meteor Organization (IMO) on the near-maximum Perseid visual results collected by 222 observers around the world (published in WGN, the Journal of the IMO 30:6 (2002 December), pages 232-243). This report gives an overview of how the Perseids behaved in 2002 August.

The Observers

The list of observers active in August follows, and as normal, it includes those who reported successful watches, and those whose efforts were thwarted by clouds but who still troubled to send in details. Visual observers in England have no additional notes given. Those elsewhere are listed with the country they observed from. Non-visual observers are denoted by the letters "R" = radio, "RM" = radio data from Radio Meteor Observation Bulletin 109 (August 2002; website: http://www.rmob.org) kindly provided by editor Chris Steyaert, or "V" = video. A "+" sign before the letter indicates the observer also carried out visual watching. The German Arbeitskreis Meteore (AKM) data were chiefly taken from their journal Meteoros 5:9 and 5:10 (2002) submitted by Ina Rendtel (website: http://www.meteoros.de), while the American Meteor Society (AMS) results came primarily from their journal Meteor Trails 17 (December 2002), presented by Bob Lunsford (website: http://www.amsmeteors.org). I am especially grateful to the named societies above, who have been willing to share their data with us.

AKM observers (all in Germany, except where noted): Rainer Arlt, Pierre Bader, Orlando Benitez-Sanchez (Canary Isles; V), Lukas Bolz, Frank Enzlein, Darja Golikowa, Daniel Gruen, Ralf Koschack, Detlef Koschny (Netherlands; V), Hartwig Luethen, Sirko Molau (+V), Selina Mueller, Sven Naether, Mirko Nitschke (V), Steve Quirk (Australia; V), Juergen Rendtel (+V), Ulrich Sperberg (V), Rosta Stork (Czech Republic; V), Joerg Strunk (V), Heinrich Wiechell (Greece), Roland Winkler, Oliver Wusk, Ilkka Yrjola (Finland; V, RM); AMS observers (with their observing States in the USA or countries outside the USA): Ardalan Alizadeh (Iran), Jure Atanackov (Slovenia), Javad Azizi (Iran), Malcolm Currie, Thomas Davis (Texas), Vincent Desmarais (Quebec, Canada), Vincent Giovannone (New York), George Gliba (West Virginia), Jonathan Gore (North Carolina), Cathy Hall (Ontario, Canada), Amir Hasanzadeh (Iran), Robert Hays (Indiana), Carl Johannink (Netherlands), Edwin Jones (Arizona), Javor Kac (Slovenia), Soheil Khoshbinfar (Iran), Gene Kispert (Minnesota), Marco Langbroek (Netherlands), Pierre Martin (Ontario, Canada), Paul Martsching (Iowa & South Dakota), Ashley Matous (Kansas), Bert Matous (Kansas), Jim McGraw (Iowa), Norman McLeod (Florida), Alan McRobert (Massachusetts), Ali Moosazadeh (Iran), Michael Morrow (Hawaii), Dennis O'Day (Florida), Mazyar Seyyednezhad (Iran), David Swann (Oklahoma), Richard Taibi (Virginia), Rocky Togni (Arizona), Kim Youmans (Georgia); Enric Fraile Algeciras (Spain; RM), Dirk Artoos (Belgium; R), Mike Boschat (Nova Scotia, Canada; RM), Walter Boschin (Italy; RM), Jay Brausch (North Dakota, USA), Michael Brooke, Jeff Brower (Colorado, USA; RM), Dave Campbell, Chris Chambers (Bulgaria), John Chapman-Smith, Terry Churms, Maurice de Meyere (Belgium; RM), Minoru Ehara (Japan; RM), David Entwistle (R), Steve Evans (V; data also listed in AKM journal), Valter Gennaro (Italy; RM), Ghent University (Belgium; RM), Shelagh Godwin, Patrice Guerin (France; RM), Alan Heath, Philip Heppenstall, Tomislav Jurkic & Petra Korlevic (Croatia; RM), Michael Krocil (Czech Republic; RM), John Lambert, Bob Lunsford (California, USA; part of data tabulated with AMS results), Edward Mallett, Tony Markham, Alastair McBeath, Simon McBeath, Tom McEwan (Scotland), Jane Mills, Toshihide Miyake (Japan; RM), Stan Nelson (New Mexico, USA; RM), Robert Obraz (Croatia; RM), Hiroshi Ogawa (Japan; RM), Robert Savard (Quebec, Canada; RM), Jonathan Shanklin, George Spalding, Enrico Stomeo (Italy), Dave Swan (RM), Pierre Terrier (France; RM), Stanley Toyn, Shinji Toyomasu (Japan; RM), Yung Cheich Tsao (Taiwan; RM), Takashi Usui (Japan; RM), Jan Verbert (Belgium), Julie Yellowley, Bruce Young (Queensland, Australia; RM).

Shower Overview

The three graphs here illustrate how our reporters saw the Perseids. As the first graph shows, Perseid coverage was possible on every night between August 1-2 to 17-18 inclusive, one of the very best runs across the Perseid maximum the Section has ever enjoyed. The next best from recent times was in 2000 (see the Perseids 2000 page of this website), when moonlight truncated the graph after August 13-14. The mean Zenithal Hourly Rate (ZHR) datapoints show Perseids becoming quite obvious to dedicated watchers (ZHRs ~10) by August 3-4, picking up to a casually-detectable level (ZHRs ~25) by August 9-10, before shooting up to strikingly obvious numbers between August 11-12 to 13-14. The decline was rapid, back to below ZHRs of 10 by August 17-18.

per02zhr.gif

The near-peak ZHRs of August 11-12 over the USA give a slightly false impression of two maxima, because of the gap in data coverage between 10h and 22h UT on August 12. In all probability, rates continued at about similar levels between these times. As the second graph here demonstrates, now using 30-minute intervals where possible to compute the mean ZHRs from (thus preserving more of the fine detail in these highest rates), ZHRs settled into pretty much of a plateau for much of August 12-13, without producing any clearly defined maxima during that time. The main maximum was anticipated around 22h30m UT, with two possible additional maxima from recent returns around 20h15m and 08h30m UT on August 12-13. There is no sign that these were found here, nor in the IMO results, which latter gave the marginally highest ZHR, ~ 106 +/- 3, around 01h UT on August 13.

The highest ZHRs, based on the half-hour means on August 12-13 in SPAMS data, were at 22h30m (82 +/- 5), 02h30m (81 +/- 9) and 04h30m UT (81 +/- 10), with the mean overall ZHR between 22h-04h UT = 74 +/- 7. In general, the highest rates show up rather marginally compared to times to either side, reinforcing the plateau-like appearance. How significant the brief 22h30m UT ZHR peak was is unclear; probably not very. The 22h-04h interval produced the better rates, as the overall mean ZHR between 04h-10h UT was slightly lower at 69 +/- 9. All the ZHRs here were based on an assumed population index (r-value) of 2.6, and were calculated from intervals where the limiting magnitude was +5.3 or better, the cloud cover below 20%, and where the Perseid radiant was at least 20 degrees above the horizon.

The third graph demonstrates the magnitude distributions for 1127 Perseids and 265 August sporadics seen in similarly better-sky conditions, along with corrected mean magnitudes. Too few train datasets were available for a full analysis, but 32% of Perseids and 7% of sporadics left persistent trains as a whole in our results.

The radio observers did not enjoy the best of times in August. Apart from the traditional summertime problems with interference due to the Sporadic-E propagation mode, several European radio workers suffered equipment failures or power cuts at the least helpful times near the Perseid maximum. Allowing for these difficulties, a clear peak was apparent in surprisingly few European results, while even the Japanese observers, who generally recorded the Perseid maximum more obviously, often found the radio meteor counts for several days to either side of August 12-13 made the Perseids stand out relatively poorly. Two graphs here illustrate these points, taken from RMOB data produced by Dave Swan in England and Hiroshi Ogawa in Japan. The symmetrical curves, keyed to the right-hand y-axes, show the Perseid radiant elevations for each site, while the irregular traces give the raw hourly meteor echo counts. Times when this trace drops to zero show periods when no accurate recording was possible because of interference. This radio information tends to support the general visual findings, with a somewhat lower, but more protracted, Perseid peak than has been seen for some time.

Observers' Impressions Near the Perseid Peak

Details from British locations on August 12-13, including a selection of newsgroup messages thoughtfully forwarded by other observers, indicated south-east England came off best for clearer skies. Positive reports arrived from Kent, Sussex, Surrey, the London area, Middlesex, Buckinghamshire, Oxfordshire, Hertfordshire, Bedfordshire, Cambridgeshire, Suffolk and Norfolk in East Anglia, with sites in Gloucestershire and the West Midlands the furthest west to enjoy better conditions. Northwards, Nottinghamshire, South and West Yorkshire and Northumberland saw several observers active too, but south Devon, Dorset, Wales, Staffordshire, Northern Ireland and south-west Scotland were stuck with clouds only.

Many of the clearer sites still had problems with clouds at times, and few UK reports with limiting magnitudes better than +5.0 to +5.3 were received, which is why the limiting magnitude criterion for computing ZHRs and the magnitude distributions was relaxed from its normal, more rigorous, value of +5.5. Most people, though not all, seemed satisfied by what they saw however, as there were several good Perseid fireballs about, including a notable one around 22h01m UT spotted from nine sites across south-east England. While Perseid fireballs are commonest close to the maximum, it is certainly unusual to get so many reports on any one of them, and indications are this was an especially bright event to be so noteworthy, perhaps around magnitude -6/-8 at best. Unfortunately, most watchers were rightly concentrating on getting accurate Perseid counts that night, and too few of the lucky witnesses were able to give details on the fireball's sky-position, insufficient to even estimate where the meteor might have passed directly over. Observed Perseid rates sometimes reached one or two meteors a minute briefly, a good display, but well short of the strength of some seen in the past decade.

Mainland Europe had dismal conditions, with clouds and heavy rain across much of the Continent during the Perseids' best. Indeed, there were some serious flooding problems in places. On maximum night, the most positive news came from Bulgaria, Greece and southern Italy, with a few observers managing to snatch at most a couple of hours of better skies further north, in north and north-west Germany, parts of the Netherlands and Belgium (here only some notes from Jan Verbert, who enjoyed just one 7-minute clearer spell all night!). By contrast, UK observers had by far the better luck.

Among the reporters further afield on August 12-13, the Iranian group who provided data via the AMS had some moderate conditions, but only short watches were possible under at times poor limiting magnitude skies. In eastern North America, Ontario and Quebec in south-east Canada, and Virginia in the eastern USA had the clearer skies, even so typically with quite poor limiting magnitudes. Elsewhere in the USA, only observations from North and South Dakota and California appeared, but here at least, skies were much more transparent. As our ZHR graphs show though, Perseid ZHRs were already below their best by the time night had fallen over much of North America.

Perseid images

Two composite video-still Perseid images are shown here from those collected by Steve Evans in Gloucestershire. Both were taken using his CCD video system "Emily", fitted with an 18mm second-generation MCP image intensifier and a 50mm f/1.4 lens, giving a field of view of 21 degrees and a video-stellar limiting magnitude of +6.5. Only every other frame has been stacked to construct the images, giving breaks in the meteor trails which allow us to measure the apparent velocities of the meteors, which along with the path lengths and directions enable us to confirm both were Perseids.


Image 1. August 13-14, 22:46 UT. A Perseid passing very close to Delphinus the Dolphin, seen inverted near the centre of the field, as south is to the top of the image.

Image 2. August 15-16, 22:21 UT. A Bright Perseid caught between Sagitta the Arrow (left), Delphinus (right), and Aquila the Eagle (top - the brightest star to the top left is Altair, Alpha Aquilae). South is to the top of this inverted image again.

Conclusion

The primary Perseid maximum, first seen in 1988 and followed throughout the 1990s (last seen in 1999), does now seem to have disappeared, much as expected. However, theoretical calculations indicate it may revive again in 2004-2006. Time will tell, as usual! The tertiary peak, seen in 1997-1999 after the "traditional" maximum had ebbed, does not seem to have featured at all in more recent times. Watchers need to be alert to these possibilities, especially when future moonless returns are in prospect.

Very many thanks go to all the observers and correspondents who have provided the details included in this report. Good luck and clear skies for your next watching!

Report prepared by Alastair McBeath, SPA Meteor Section Director

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