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(meteorobs) Re: zenithal attraction
Rob McNaught wrote:
> Do observers compensate for zenithal attraction in the radiant in >assigning a meteor to a radiant?
For the majority of cases zenithal attraction is not taken into account.
This correction is usually so small that it need not be taken into
consideration. Most of us watch showers when the radiant is at least 20
degrees in altitude and even for meteors as slow as 20 km/sec the
zenithal attraction is only 3 degrees at that altitude. This is still
smaller than the expected error from plots or direct shower association.
For those of you not familiar with zenithal attraction, it is a
deviation caused by the gravitational field of the Earth. Meteoroids
encountering the Earth are accelerated and deflected. This deflection
shifts the observed radiant toward the zenith (90 degrees altitude or
straight up). The amount of shift depends on the velocity of the
meteoroid. Slower meteoroids will be deflected to a greater degree and
will have a greater zenithal attraction. Showers such as the Perseids
and the Leonids suffer little zenithal attraction. On the other hand,
evening showers with low altitudes can see their radiant shift upwards
as much as 15 degrees.
Bob Lunsford
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