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(meteorobs) Ursids active or not - Or unusual stream composition?
The visual observations reported here paint a very confusing picture
of the Ursids "peak" around 07:30 UT Dec. 22.
Some observers report enhanced activity:
Peter Jenniskens wrote:
"The Ursid shower did flare up significantly last night between 5 UT
and9:30 UT, with a peak around 7:20±10 UT, close to the predicted
maximum at 7:29 UT."
Marco Langbroek wrote:
"the trends suggest a peak near 7:30 UTC indeed, as predicted by
Peter and Esko, with peak rates (interpolated) probably around
ZHR ~75."
Even one estimate at ZHR=200!
Obs: Peter Gural
UTC Teff Lm Urs Spo ZHR(Urs)
08:01-08:10 0.15 6.2 10 2 200±65
Of course, this was just a 9 minute Teff! Periods less than 20 or 30
mins for a lower activity shower may be subject to severe
statistical fluctuation.
ON THE OTHER HAND others reported little activity:
Robert Lunsford wrote:
"Rates were quite low the first two hours and the expected
maximum came and went without much activity."
Dan Taylor reported from Ontario:
>Ursids
>*all times in EST
> Ursids mag Lim. Mag.
>8:10-8:35 0 - 5.5
>2:14-2:43 2 3m,4m 6.0
>3:15-3:46 3 3m,5m,5m 6.0
>4:14-4:31 1 5m 6.0
Eric Flescher reported from Kansas:
"...the skies were crisp clear and the weather really cold.
I went out and at 1:38 so a beautiful slow moving fireball (mag -3),
Otherwise saw 2 other sporadic 2 magnitude but no ursids. Since
the storm seemed not to show , I retired 30 minutes later."
In addition, the Czech Ondrejov backscatter radar did not show any
enhanced activity from 06:00 - 09:00 UT.
MY OBSERVATIONS under pretty good conditions (LM 5.6 6.1
6.0) covering the peak period from 05:40 - 08:30 UT also showed
very low rates, well below Sporadic. Even adjusting using my pretty
big correction factors like 7 and 4, my best ZHR only hit 14.3, and
the "peak" hour from 06:50 to 07:52 had only 1 URS which
converts to a 3.8 ZHR! Unfortunately, I quit at 08:30 UT so cannot
confirm the Ursid mini-outburst between 08:00 - 09:00 UT that
Robert Lunsford observed.
I don't know what to conclude from these divergent reports around
the same "peak" time of 07:30 UT on Dec 22? Some observers
saw fairly decent activity, other practically none. I suppose it could
be attributed to statistical variation, but the differences are quite
large for that. Another possibility could be a very "clumpy"
meteoroid stream. Rather than being typically distributed in space
like most others, this Ursid stream may have had locally denser
patches interspersed with relatively sparse areas. This could
explain the large differences in visual rates seen at various
locations. But would it explain the lack of enhancement by
backscatter radar? I don't know enough about the FOV or volume of
space covered by this device to judge if it could distinguish such
variation.
I guess we should wait and see what the final report conclusions
are from everything submitted to IMO for this weird shower.
Merry Xmas and Happy New Years to all!
Mike Linnolt.
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