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Re: (meteorobs) Two question regarding meteor rates?

This has been a fascinating thread, folks - thank you to David
Entwistle for posting his original question! For one thing, it
is great to have any excuse to reread Peter Jenniskens' seminal
"Meteor stream activity" papers again - I through VI... :)

And I have to say with a little embarrassment, that I learned
some important things myself, from Geert and Marco's answers:
as a matter of fact, my vague recollection was that at least
part of the annual sporadic rate variation was best explained
by the inclination of Jupiter's orbital plane to our own! (So
I would have expected, for example, that Bob Lunsford's loose
Northern Apex "sporadic radiant", should have actually had a
superimposed component of seasonal variation UNRELATED to its
peak nightly horizon angle at any given location...)

Did anybody else share this same recollection? I ask because
I wonder where it came from - in other words, which reference
over the years I had managed to misinterpret or misremember,
to come up with this idea! :)


>The ITU-R recommendation P.843.1, which covers meteor burst
>propagation, suggests a northern hemisphere sporadic rate for
>August, which is four times the February rate.

There are a lot of minor showers active during parts of August,
David, in addition to the mighty Perseids. Is it possible that
this ITU-R document includes in "sporadic" rates, any meteors
which are not from the small handful of major annual showers?


Clear skies,
Lew Gramer



> -----Original Message-----
> From: owner-meteorobs@atmob.org
> [mailto:owner-meteorobs@atmob.org] On Behalf Of David Entwistle
> Sent: Monday, April 26, 2004 2:09 PM
> To: meteorobs@atmob.org
> Subject: Re: (meteorobs) Two question regarding meteor rates?
>
>
> In message <000f01c42af1$1d0c3240$9600000a@HAL>, Marco Langbroek
> <marco.langbroek@wanadoodot nl> writes
> >
> >The latter. See P. Jenniskens: Meteor stream activity I. The
> annual streams.
> >Astron Astroph. 287 (1994), 990-1013
> >
>
> Marco,
>
> Thanks for the excellent references. I've got hold of a copy of the
> first from here:
>
> http://adsabs.harvarddot edu/cgi-bin/nph-bib_query?1994A&A...287..990J
>
> Discussing sporadic rates, it states, 'This annual variation is mainly
> due to the position of the ecliptic, with sporadic activity
> being higher
> for a higher position of the ecliptic on the sky'.
>
> That's pretty clear and I think I see why I'm slightly confused.
>
> If I'm understanding the information plotted correctly, peak
> night-time
> (22:00 to 04:00 local time) sporadic rates, for the northern
> hemisphere,
> are expected at solar longitude 260 - 270 degrees (December)
> and minimum
> night-time sporadic rates are expected at solar longitude 80 - 90
> degrees (June).
>
> However,  it may also be correct to expect maximum day-time sporadic
> rates (of interest to the radio observer) to occur in June,
> with a day-
> time sporadic minimum in January. Total sporadic rates, including both
> day-time and night-time, should be fairly constant.
>
> The ITU-R recommendation P.843.1, which covers meteor burst
> propagation,
> suggests a northern hemisphere sporadic rate for August, which is four
> times the February rate. This presumably covers both day-time
> and night-
> time activity. They don't provide any reference for this
> conclusion and
> it could simply be incorrect.



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