The Netherlands experienced clear skies and frosty weather on December 21-22. Fast rising rates were seen at the end of the local night just before the predicted peak time (figs. 1 & 2). This is confirmed by German visual observations and German image intensified video systems as reported by Sirko Molau (IMO). Fast declining rates were seen from California, USA, short after the predicted peak time, as reported by Peter Jenniskens (NASA/Ames) (fig. 2). Combined, they suggest a shortlived peak with peak rates near ZHR ~50-75 around 7:30 UTC. Radio Meteor Scatter data by Ylkka Yrjöla and Esko Lyytinen, both from Finland, give a shortlived peak centered near 7:20 ± 10m UTC. Video-rates obtained by a NASA image intensified set-up in California also show a peak. Japanese visual observers report high rates near 7-8h UTC. It seems an outburst indeed happened, although US data so far are scarce and confusing and the Ondrejov radar did not detect the event.

More Ursid 2000 results with recent updates and a link to download a pdf version of Jenniskens & Lyytinen in press can be found on the website of the NASA MAC mission. More Dutch results can be found on the website of the Dutch Meteor Society. Below are my raw data and the IMO Shower Circular issued by the International Meteor Organization on the outburst.

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I M O S h o w e r C i r c u l a r

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U R S I D S 2 0 0 0



The 2000 return of this shower was eagerly awaited because an enhanced
activity was expected. Indeed, the rates were significantly higher than
the average. The last reported Ursid activity enhancement occurred on
Dec. 22, 1996 at solar long. 270.7 with ZHR of the order of 30.

In 2000 the conditions were good as the Moon was almost new. The long
northern nights allow a good overlap. Unfortunately, this first summary
indicates that the most interesting period is not well covered. Most
European observers had to finish around 6h UT (morning twilight). The
number of North American data is scarce so far. As a consequence, we
cannot yet achieve a good profile. Below find the preliminary data.
The high ZHR at the end agrees with Japanese data published here before,
although the errors are still quite large.

We are very grateful to the following 15 observers who sent in their reports
in time for this first activity overview:

ARLRA Rainer Arlt (Germany)
BADPI Pierre Bader (Germany)
BUCAN Andreas Buchmann (Switzerland)
CANED Ed Cannon (USA)
ENZFR Frank Enzlein (Germany)
HOSDA Dave Hostetter (USA)
LANMA Marco Langbroek (Netherlands)
LUNRO Robert Lunsford (USA)
LUTHA Hartwig Luthen (Germany)
MOLSI Sirko Molau (Germany)
OSAKA Kazuhiro Osada (Japan)
PUNMI Milesh Puntambekar (India)
RENJU Jurgen Rendtel (Germany)
STOEN Enrico Stomeo (Italy)
ZHUJI Jin Zhu (China)


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Date Time (UT) Sollong nObs nIND nURS ZHR
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Dec 22 0240 270.553 5 4 16 5.1 +- 1.2
22 0330 270.586 12 9 46 8.2 1.2
22 0410 270.620 16 9 76 12.7 1.5
22 0510 270.658 16 10 104 19.6 1.9
22 0535 270.676 8 6 58 26.1 3.4
22 0935 270.847 2 2 29 53 10

Solar longitudes refer to equinox J2000.0. nObs is the number of
individual observing periods, nIND is the number of individual
observers providing them, nURS is the number of Ursids seen. The
population index used was r=2.5. The expectation value of the ZHR,

ZHR = (1 + sum nGEM) / sum(Teff/C),

was used for the averages here, where Teff is the effective observing
time and C is the total correction composed of limiting magnitude,
clouds, and zenith correction [sin (h_R)]. Times are rounded to the
nearest 10 minutes.


Juergen Rendtel

25 Dec 2000

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