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Re: (meteorobs) Radiant position question



>> Is there a known minor shift affecting shower radiant's position
>> over a certain amount of years? If yes, how significant is this?
>> Pierre Martin
>
>Hi, did anyone ever find a suitable answer for Pierre's question? I'd be very
>curious to hear myself! Gary K., are you aware of any historical evidence for
>radiant drifts? It'd seem like the progression of nodes (or whatever the sky
>motion associated with precession is called) would have SOME measurable
>effect
>over a century or more, let along possible drifts in the meteoroid streams
>themselves... How about it, anyone?
>
>Lew

Yes, there can be a gradual shift in radiant position and date of activity,
with the latter being most likely.

Precession generally affects all meteor streams. For instance, we now see
the Perseids on the night of August 11/12, but it was around August 9/10
when it was first studied during the 1840s.

Gravitational perturbations can adjust a meteor stream's orbit, with those
with low orbital inclinations suffering the greatest effects. Just look at
the diffuse nature of the various radiants in the Leo region during
February and March, the Virginid region in April and May, and the
Capricornid-Aquarid region during July and August. In every case there are
several closely-related radiants, with rather long durations, and
relatively flat maximums.

Perturbations tend to have a scattering affect rather than producing an
overall shift in the radiant position or date of activity. For example, if
we had a nice evenly distributed stream that occasionally passed close to
Jupiter, only those meteors that were close to Jupiter at the time of the
encounter would be pulled into a different orbit. After the first encounter
we would have the old meteor stream, plus a new stream which may or may not
still encounter Earth. If the perturbation is minor, then another radiant
might appear or the date of maximum might be shifted by a few hours or
days.

Gary



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