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(meteorobs) Re: Geminid visibility range and rates
The Geminid radiant declination is +33, so the radiant passes overhead for
anyone at latitude 33N at about 2 am local time. The complement of 33
degrees is 57o, thus north of latitude 57N the radiant is circumpolar. The
southern limit would be 90 degrees of latitude south of 33N, or 57S, taking
in all land areas except Antarctica. Going further south of about 20N
becomes progressively less favorable as the radiant becomes lower combined
with shorter nights.
On the max night of Dec 13/14 the peak is actually broad enough to last for
a full day. Everyone gets to share in the best rates around midnight to 4
am local time. I like to break the earth down into four general zones.
Here is what I expect each zone to see. Pacific - max the night before (Dec
12/13) with mostly fainter Geminids, then Dec 13/14 mostly bright Geminids
with rates cut in half. Asia - mostly faint Geminids. Europe - mix of
faint and bright Geminids. America - mix of faint and bright Geminids.
As for the peak rates, I see low 80's/hour in dark skies year after year.
The Geminids are the most reliable shower of the year, "reliable" meaning
"consistently the same." There have been a handful of hours over 90, but
only once have I broken 100 (in 1979 at 103 Geminids/hour.) Numerous
active observers have better perception for meteors than I do; some are
capable of seeing two times or more my rates. I see about what the general
public sees.
From semi-urban skies expect about half my rates, and from a fully urban sky
only a fifth. These are the fractions I have obtained under less-than-ideal
conditions.
On the nights preceding max I typically see 40/hour one night before,
20/hour two nights before, 10/hour three nights before, and 5/hour four
nights before. It's just a curious coincidence that rates double night to
night for four nights. For the night after max I expect 20/hour at best,
and usually 15 or less, then two nights after it drops to less than 10/hour.
The radiant rises here in SW Florida (latitude 26.5N) at about 730 pm local
time, so the first earth grazers would begin then. In the first hour I
wouldn't expect over 10 at best. North of here the grazers would start
earlier, probably an hour or more earlier in New York. Times need not be
precise as for eclipses. If observing time is limited, spend maybe half an
hour watching for grazers early, then an hour later on for much higher rates.
In 1996 the max night came one day earlier because of leap year : using
complete hours with no clouds sky 7.3 1126-526 EST, Geminids were
79,79,85,96,42,46. Got the second-best hour ever with the 96 that year.
In 1979 the max was on the regular Dec 13/14. EST hours 825-225 in sky
LM7.0 I saw 21,38,74,71,103,88 Geminids. These prior years illustrate what
the Geminids are capable of doing. I tend to skip the earliest hours to
favor the rich later hours by staying awake.
Norman
Norman W. McLeod III
Staff Advisor
American Meteor Society
Fort Myers, Florida
nmcleod@peganet.com
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