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rövidesen. Kérném szépen ebben az angolul jól fordítók szíves segítségét!

Tepi)



From: Peter Jenniskens
Subject: New shower from comet C/1999J3 ?


Will there by a meteor outburst from comet C/1999J3 this year?


There has been some excitement about the possible meteor outburst activity
of long period comet C/1999J3. The comet is expected to pass fairly
close to Earth´s orbit, at 0.0115 AU outside of the Earth´s orbit, and
at a location that we will pass on November 11.82 UT.

This is a long-period comet, with a period of some 63,000 years long.
This type of comets cause "far-comet" type outbursts, i.e. outbursts that
do not correlate with the return of the comet to perihelion. Instead,
the planets cause a dust trail in the comet orbit to move in the Earth´s
path once in a while. Typically once or twice every sixty years.
The showers are brief (less than 1-2 hours) and they occur close to the
node of the comet orbit.

The reason why the showers do not correlate with the return of the comet
is because the long period orbit causes large differences in orbital
period for individual grains that are ejected with a range of ejection
velocities. Hence, the dust spreads rapidly along the comet orbit during
even a single orbit, and quickly dillutes so much as to be hardly detectable.

A shower from this comet may have occurred in the past, which should have
been much at the same solar longitude as the decending node of the
comet orbit. The maximum effect of planetary perturbations is needed to
move the trail by 0.0115 AU. Hence, the years when the planets
Jupiter and Saturn lined up in the right direction will have had best chance.

Hence, it is unlikely that there will be activity from comet C/1999J3
this year, unless the planets happen to favor a position of the dust
trail that is right in Earth´s path. That is unlikely.

Nevertheless, keep an eye out for the unexpected! Also, this type of
"far-comet" outbursts must occur relatively frequently all throughout the
year, many showers of which remain to be discovered.


Peter Jenniskens



                    Tepliczky Istvan  - tepi@mcse.hu