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(meteorobs) Curved meteors



In light of the recent discussion about curved meteors or meteors changing
directions, the following excerpt from WGN is reprinted below for all who are
interested about the subject.
George Z----

From "Letters to WGN", the following was submitted by Ralf Koschack in
September 1991.  

ON BENDED METEOR TRACKS.

In the August issue (WGN 19:4), p.136, Gotfred Kristensen (Denmark)
reported his observation of a bended meteor track.  In an editorial comment
it was added that a meteor entering the atmosphere under a very low angle can
bounce back on a denser layer of air, thus causing a bended meteor track.
From Ralf Koschack (Germany) we received the following criticism to this
suggestion.

The editorial remark concerning the unusual meteor track is generally true,
but such an effect can only be the result of a meteoroid moving parallel to
and in the vicinity of the horizon.  Otherwise the perspective does not allow
to detect the slight change of direction.  In the reported case the meteor
moved nearly exactly along an azimuth great circle.  For such meteor changes
in the altitude above the Earth's surface, cannot possibly be detected as
changes in the direction.

Generally, dramatic changes in a meteor's direction are impossible.  This
follows from the simple rules of mechanics. In the reported case, the
original direction of flight became zero as the meteor changed it's direction
by 90 degrees.  Let us estimate the necessary force.  The change of direction
took place within about 0.05 seconds.  In this time span a force must have
been exerted.  For a meteor of magnitude +2.5, the mass is about 0.05 grams
for a velocity of 30km/s and 0.0025 grams for a velocity of 60 km/s.  In the
first case a force of 30 N and in the second case one of 3N would have been
necessary.  We see there are many impossibilities:

1)  Where should a well defined, short activing force of this order come
from?
2)  A particle would not survive the action of such as force.

This means that only very slight changes in meteor direction can be
considered possible.  More dramatic changes in the direction have their
origin in the perception by the observer.  A short, reflex-like closing of
the eyes for instance can cause parallel shifts (as reported) or tilts.