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Re: (meteorobs) Re: Best Time to See the Leonids
Lew queried, in his cloud tainted way: :->
>And that raises yet another question! :) Thanks to a shallow ecliptic
>angle at London's latitude, the LEO radiant at this year's max rises
>VERY slowly: between 10 and 11pm, it's elevation goes from -1o to 6o.
>Assuming a constant meteor storm(!!) of 1 meteor per second through-
>out that hour, how slowly would the perceived rate increase?
To put it succintly, as I understand it, who knows!
As you well know, correcting rates for radiant elevation is a messy enough
process when the radiant is higher...most correctors really only crunch the
numbers for elevations greater than 20 degrees....using a set of
assumptions that are valid at reasonable angles. (such as atmomospheric
extinction, hiding behind the horizon, area of meteor height covered by
your field of view, etc). However, again in the big yellow book, below 20
degrees, the validity of those assumtions is suspect. I believe (and I
could be wrong) that the IMO does not use data with elevations below 20
degrees for calculating ZHR due to the "nonlinear" extension of those
corrections. IOW, while we can make some reasonable assumtions above that
height, below there too many unknowns to make reliable corrections; hence
the inverse, trying to predict rates with a known ZHR would be just as
unreliable. If you want to get in the ballpark, you can just run the ZHR
corrections in reverse with those radiant elevations, but the accuracy of
those predictions would probably be MUCH worse than usual.
I'm sure some others will expand this discussion, so since I don't
have my references in front of me, I'll stop now before I get in too
deep...perhaps when I have the papers in front of me I'll throw out some of
the theory in more detail.
Wayne