(meteorobs) Geminid report from Edmonton

Bruce McCurdy bmccurdy at telusplanet.net
Tue Dec 14 19:36:16 EST 2004


    (counts to follow by separate post)

    It's great having a weather expert as an observing buddy. My great
friend Alister Ling called it perfectly, yet again, on Saturday afternoon
calling for unbroken clear sky Sunday/Monday, and patchy cirrus and worse
for Monday/Tuesday. Allowed me to plan my weekend perfectly. Here it is 2
a.m. Tuesday and I'm inside drafting this report and listening to the
weakening radio Gems, thanks to patchy cirrus and worse. But last night
(Dec. 12/13) was a beauty.

    I had hoped to be dark-adapted and counting by 2300 MST, but had a
disconnection event in which I misplaced my car keys. My penalty was paid
immediately: between the moment I opened the car door at Blackfoot and the
one when I put my foot on the ground, a huge roar was heard from Larry Wood.
It was about a -8 magnitude roar, but after applying the Larry Factor (2x) I
guessed that Larry had seen a -4 meteor. Which he had, right in the
direction that I would spend the next five hours looking. Sorry, Alister.

    Because certainly one of the stories of the night was the total absence
of bright meteors. Over the next five hours I counted 414 meteors, and only
a single one of them did I place at even mag -2. It was really quite
astonishing.

    There was, however, a plethora of garden variety meteors and a fun time
was had by all. I experienced my third highest one night total ever:

    2001 November 18    1594 Leonids, 1610 total meteors (6 hours)
    1996 December 13      412 Geminids, 484 total meteors (5 hours)
    2004 December 13      363 Geminids, 414 total meteors (5 hours)
    1994 August 12           361 Perseids, 403 total meteors (7 hours)
    2004 August 12           334 Perseids, 361 total meteors (5 hours)

    So 2004 hasn't been such a bad year.

    Now I suppose if a guy was really on the ball, he could do the 6 to 6
shift with the Gems, but I was the guy who couldn't find his car keys so
five hours was stretching the limits of my concentration on this occasion. I
spent the entire time facing just east of due south and watched the radiant
rotate right past me, giving me a very cool sense of Earth's ponderous but
inexorable spin. I noted for not the first time, that given their radiants'
relative position in the sky one might expect the Geminds to be a month
before the Leonids rather than a  month after; and made the more general,
perhaps obvious observation that the more easterly the radiant at local
midnight, the faster one can expect its meteors. With the exception, I
guess, of a shower like the Quadrantids which is so far east at local
midnight it's actually north. No doubt there are secondary factors like
differing orbital velocities of the various meteoroid streams, but it seems
like a good rule of thumb.

    Certainly the medium-speed Gems are a different animal than the Leonids
and Perseids, seeming to rain down almost perpendicularly. I noted that most
had short wakes and trains which persisted less than a second at best. I
also was disappointed my a paucity of colourful meteors, the vast majority
were shades of white. Only a few displayed tinges of orange, green and blue
to my perhaps colour-poor vision.

    Conditions were very good at Blackfoot, which is rated about 4.5 on the
Bortle scale.Limiting magnitude was consistently around mag 6.1, at least
towards the south. There was a finely structured and very pretty aurora
which kicked up along the northern horizon at times but never really invaded
the south, but no signs of cirrus or other meteor killers. Temperature
gradually dipped below -10° C.


    As has become our custom, we tuned in to FM 92.1 on my car radio, and
for a couple of hours I kept tabs of those visual meteors which had obvious
audio counterparts. The sample bins had 29 simultaneous 'hits' out of 136
observed meteors.

     The best bin of the night occurred between 230-240 MST when the radiant
was cresting the meridian. The bin started with an overdense meteor which
delivered the spooky intro and opening verse of the Phil Collins classic,
'(I can feel it coming) In the Air Tongiht', another radio meteor for my
greatest hits list. It was like a harbinger, because the next few minutes
the sky was alive with meteors. One highlight was a matched pair which
Alister and I agreed looked like the splitting of a single object: same
speed, same brightness, same duration, exact same moment, appearing to
diverge from a common point, EXCEPT one was a Geminid (emanating from a more
distant point), and one was not. Then I experienced ten in under a minute
including four in about ten seconds and then a second grouping of four in
about two seconds. This last bunch was remarkable in that all occurred near
the eastern horizon between Coma Berenices and Arcturus, and all four
roughly traced back to both the Geminid and Coma Berenicid radiants. The
meteors seemed too fast to be Geminids, but too close to the Coma radiant to
appear that fast, so I was temporarily confused. It could be that the
rapid-fire nature of the outburst made the individual meteors seem faster.
After much pondering I decided they weren't a sudden outburst of Comids and
called them Geminids. I finished that bin with 22 Gems plus a couple of
Monocerotids and the night's only sigma Hydrid.

    Although I am now at an age where I pay a physical price for the
occasional all-nighter, I had hoped to get out for a few hours Monday
night/Tuesday morning for the expected showing of brighter meteors, but saw
none among the breaks in the clouds in only a few minutes of trying from my
urban back deck. However, I did crash while writing this report and am only
completing it on Tuesday evening.

    I will send the visual counts by separate post for those who can use
them. In a day or two I will provide an hourly radio count for the 7-10 days
of maximum activity.

    regards, Bruce




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