[HSMS] Re: Loenid Showers Activity.

From:  Shelby Ennis, W8WN 
Subject: [HSMS] Fwd: Leonid Meteors

>From:  Joe Rao 
>Date: Wed, 19 Nov 1997 11:56:45 -0500 (EST)
>Subject: Fwd: Leonid Meteors
>Forwarded message:
Subj:    Leonid Meteors
Date:    97-11-19 11:35:02 EST
From:    Skywayinc

It appears that there was some enhanced activity with this year's Leonid
shower, although nowhere near what one would catogorize as "storm"
conditions.  Basically, from reports that I have received from a number of
observers, it appears that the Eastern U.S. saw a Leonid shower that produced
approximately 5 to 15 meteors per hour in the few hours just before dawn. . .
while the Western U.S. saw a stronger and brighter display of Leonids, with
average rates of between 15 and 30 per hour (though some with a higher
"coefficient of perception" saw rates closer to 50 per hour).  

The visual data that I have looked at from the "more experienced" observers
(John Bortle, George Zay, etc. . . ) would demonstrate clearly that any ZHR
values obtained under the bright (89% illuminated) waning gibbous Moon are
mea>ningless as absolute figures.  In addition, observations obtained under a
bright moonlit sky does not permit one to compute a reliable r-value
(population index...the overall numbers of bright versus faint meteors)  and
hence ZHR value.   I will guess that when all is over, said and done and a
more complete analysis is made, that a largely qualitative -- as opposed to
quantitative -- picture of the 1997 Leonids will be made.

Radio observations from some ham operators experienced in VHF radio scatter
techniques indicate two "peaks" of activity.  A  long-time (30+ year)
listener of  the Leonids, Shelby Ennis of Elizabethtown, Kentucky and Paul
Kelly of Milo, Maine, both report strong activity between approximately 9:55
and 10:33 UTC and again between approximately 12:22 and 13:52 UTC.
 Interestingly, the first peak came as we were approaching that point in our
orbit where the famous 1966 meteor storm occurred, while the second peak
coincided with the Earth passing the descending node of the parent comet
55P/Tempel-Tuttle.  Both Ennis and Kelly indicate that the activity,
particularly of the first peak, seemed to approach. . . though not surpass. .
  the great Perseid activity heard in 1991 and 1992.

While fireball activity was visible most everywhere, it appears that an
"outbust" of  brilliant meteors. . . in the -4 to -9 magnitude range. . .
occurred for West Coast observers, chiefly in the rough time frame of 4 to 6
a.m. PST.  During that time, many reported seeing spectacular fireballs and
bolides at intervals of just a few minutes apart.  This activity coincides
with the second radio peak noted above. . . and as such also with the time of
the nodal crossing of 55P/Tempel-Tuttle.

The undersigned suggests that there is a filament rich in large particles
that is moving ahead of the comet; dusty material ejected fairly recently
 (within the past one to three revolutions).  This densest part of this
filament  might be only as wide as 0.003 a.u. or less.  Earth may have
interacted directly with this filament in 1799 and 1832, producing
spectacular meteor storms. . . but with our being much farther removed from
the comet orbit this year (0.008 a.u.) we did not get a true storm, although
we did encounter large particles located immediately outside of this supposed
dense filament on Monday morning.

It is hard to access exactly what will happen in 1998 and 1999 with the
Leonids, especially since we will begin to sample material to the rear and
not the front of the parent comet.  At this juncture, the only thing that can
be said is that it "appears" that significant activity will occur near the
nodal crossing time next year (19:43 UTC on November 17) with another surge
coming about 2-3 hours earlier (lining up with the solar longitude of the
1966 storm). As to whether we get a stupendous storm of meteors or merely a
moderatly strong shower consisting of fireballs and bolides (as was the case
with the 1965 Leonids) is a question whose answer we all find out just under
one year from now. . . 

   -- Joe Rao
    Skyway, Inc.   


Comments: Rein, W6/PA0ZN

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