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Re: (meteorobs) Radiant rising time
> Robert: "Zenithal attraction" is a new term to me. Can you take a minute
> to explain it? Should this effect be taken into consideration if one is
> determining the time of a radiant's rising for the purpose of watching for
> tangential meteors or "skippers?" If so, what is its value, or how is its
> value determined?
> George Kelley
George, my response will be lightening quick, so please email back if this
answer doesn't make sense! Zenithal attraction is the tendency for all apparent
meteor radiants to be shifted a short distance (usually degrees or tenths of a
degree) toward your zenith. This is because all meteoroids, as they fall into
our atmosphere, are suddenly deflected from their true orbits (which are what
determine their "true radiant" in the sky) by Earth's gravity. This effect is
generally very tiny for fast meteors, but becomes more significant the slower
the meteoroid is moving relative to earth. (For folks who know about vectors,
this is based on vector addition of the earth's velocity and the particle's!)
And yes, this WILL become important when you're trying to catch grazers! This is
especially true for the slower showers, like the Virginids currently in our
skies, or the Southern observers' Pi Puppids, soon to grace April skies.
Clear skies all, and welcome back indeed. :)))
Lew
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