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: http://star.arm.ac.uk/nibulletin/2004-Nov-5.html
Дата изменения: Mon Nov 8 14:35:19 2004
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From: TerryMoselaol.com
Date: Fri, 5 Nov 2004 19:33:50 EST
Subject: Extra Leonid activity in E Europe?
Hi all,
(NOT EXCLUSIVE to IAA)
There is a good chance of some enhanced activity from the Leonid meteors, and
over a week earlier than the main shower peak! Unfortunately we will NOT be
particularly well placed to observe this: conditions will be best for observers
in E. Europe & the Middle East.
The following prediction has been calculated by Dr David Asher of Armagh
Observatory, one of the world's leading authorities on meteor stream dynamics.
On the late evening of Monday 8 November the Earth is predicted to pass
through an old and diffuse trail of debris from the 1001AD perihelion passage of
comet Tempel-Tuttle, the parent comet of the Leonid meteors, which normally peak
around Nov 17.
Since the stream is so old it will probably contain mainly the smaller
particles, which produce fainter meteors. Rates are estimated to be from 50-100
meteors per hour in prime observing conditions. But this is the so-called ZHR, or
Zenithal Hourly Rate, which is the number of meteors per hour which would be
seen by an experienced observer, with the radiant in the zenith, in a perfectly
clear dark sky. But unfortunately at least one of those conditions will not
pertain for us!
The peak is expected to be at 23.30 UT so as the radiant (in the 'Sickle' of
Leo) will not even have risen from most of Ireland by then, we will see very
few meteors, if any, at that time. And the radiant will still be very low even
at 01.00 (less than 10 degrees for most of Ireland), when this extra early
activity is likely to be tailing off, so we will be lucky to see much happening
from here at all. Observers about 50 - 70 degrees of longitude further East
than Ireland should have the best view, as the radiant will be high up for them.
If the meteors were likely to be bright we might see some, as they could be
visible even over the much greater distance which pertains when the radiant is
low. But, reluctant as I am to dampen expectations, I doubt if we will see
more than a few meteors per hour before about 00.30 or 01.00. Of course if the
passage through the stream occurs an hour or two later than predicted, when the
radiant if higher from here, we will see more - maybe about 10-20 per hour.
Since the meteors are likely to be faint, it will be essential to observe
from a very dark site to get the best view. In particular look for a clear &
dark East to Northeast horizon as the constellation of Leo will be rising in
this part of the sky.
The later in the night, the higher the radiant rises for us, but according to
the predictions the activity from this particular stream may be over by about
01.30 at the latest.
The 'normal' peak of the Leonids should produce a reasonable rate of meteors
(maybe 30-50 per hour actual observed rate in a dark sky for us) just before
dawn on the morning of Nov 17.
Anyway, meteor showers can often produce surprises, so it will certainly be
worth looking from about 23.30 onwards on Monday evening, through into the
small hours of Tuesday morning, if it's clear.
Good Luck,
Terry Moseley
aol.com Date: Fri, 5 Nov 2004 19:33:50 EST Subject: Extra Leonid activity in E Europe? Hi all, (NOT EXCLUSIVE to IAA) There is a good chance of some enhanced activity from the Leonid meteors, and over a week earlier than the main shower peak! Unfortunately we will NOT be particularly well placed to observe this: conditions will be best for observers in E. Europe & the Middle East. The following prediction has been calculated by Dr David Asher of Armagh Observatory, one of the world's leading authorities on meteor stream dynamics. On the late evening of Monday 8 November the Earth is predicted to pass through an old and diffuse trail of debris from the 1001AD perihelion passage of comet Tempel-Tuttle, the parent comet of the Leonid meteors, which normally peak around Nov 17. Since the stream is so old it will probably contain mainly the smaller particles, which produce fainter meteors. Rates are estimated to be from 50-100 meteors per hour in prime observing conditions. But this is the so-called ZHR, or Zenithal Hourly Rate, which is the number of meteors per hour which would be seen by an experienced observer, with the radiant in the zenith, in a perfectly clear dark sky. But unfortunately at least one of those conditions will not pertain for us! The peak is expected to be at 23.30 UT so as the radiant (in the 'Sickle' of Leo) will not even have risen from most of Ireland by then, we will see very few meteors, if any, at that time. And the radiant will still be very low even at 01.00 (less than 10 degrees for most of Ireland), when this extra early activity is likely to be tailing off, so we will be lucky to see much happening from here at all. Observers about 50 - 70 degrees of longitude further East than Ireland should have the best view, as the radiant will be high up for them. If the meteors were likely to be bright we might see some, as they could be visible even over the much greater distance which pertains when the radiant is low. But, reluctant as I am to dampen expectations, I doubt if we will see more than a few meteors per hour before about 00.30 or 01.00. Of course if the passage through the stream occurs an hour or two later than predicted, when the radiant if higher from here, we will see more - maybe about 10-20 per hour. Since the meteors are likely to be faint, it will be essential to observe from a very dark site to get the best view. In particular look for a clear & dark East to Northeast horizon as the constellation of Leo will be rising in this part of the sky. The later in the night, the higher the radiant rises for us, but according to the predictions the activity from this particular stream may be over by about 01.30 at the latest. The 'normal' peak of the Leonids should produce a reasonable rate of meteors (maybe 30-50 per hour actual observed rate in a dark sky for us) just before dawn on the morning of Nov 17. Anyway, meteor showers can often produce surprises, so it will certainly be worth looking from about 23.30 onwards on Monday evening, through into the small hours of Tuesday morning, if it's clear. Good Luck, Terry Moseley
