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Re: Lyrid Meteor Shower Reminder

In a message dated 98-04-19 12:55:53 EDT, you write:

GeoZay<< 
 > Just a note .... The ZHR for the Geminids has been adjusted upwards in
 > recent
 > years by the International Meteor Organization. It is now at 120.

 bernd>>Your email prompted me to browse some Sky & Telescope Calendar Notes.
In
 the Dec 1996, p. 79 issue, you find that, according to the IMO, the
 maximum ZHR reached 140 in 1993, 'whereas in the late 1980s, 100 was
 more common'.
 
 Question 1: Has this specific ZHR caused the upward adjustment or has
 there been observed a steady increase ever since 1993?<<

Steady increase since 1993. Around 1995 or 1996, The International Meteor
Organization did some updating of the various showers for things such as
ZHR's, activity periods and peak nights etc. This was all based on the
previous 10 years of meteor reports from observers around the world. 
 
 bernd>>Question 2: What does this increase imply?<<

That the earth is crossing thru a thicker area of the Geminid stream than it
has in the past. Perhaps someday it will once again diminish? I believe the
Geminids are suppose to disappear in about 200 years when the stream moves in
such a position that the earth will no longer encounter it....at least for a
period. 

 bernd>>- If a comet was responsible
 for the debris, we might conclude that this comet is on its inbound leg
 and approaching Earth but, as you say, it's asteroid 3200 Phaethon and
 not a comet.<<

Yes asteroid 3200 Phaethon. The earth satellite IRAS determined this about 15
years ago? Until then it's source was unknown.
 
bernd>> The same Sky & Telescope Calendar Notes continue with another
 interesting note: 'Rates increase steadily for several days before
 maximum, then drop off quickly. THE METEORS THAT DO APPEAR AFTER MAXIMUM
 ARE OFTEN ESPECIALLY BRIGHT '.<<

I don't know about very bright meteors occuring after maximum...The brightest
I've seen usually occurs with the maximum. In my meteor reports I figured the
Mean Magnitudes of major showers and almost exclusively I will have brighter
meteors occuring with the max night with dimmer meteors occuring nights before
and after peak. What I saw of the 1993 Geminids for two nights of heavy
geminid activity on the peak nights included 25 fireballs and a mean magnitude
of 1.74 for Dec 12/13 and 1.04 for the night of Dec 13/14. Unfortunately I
wasn't able to observe any nights prior and after those dates to compare here.
 
 bernd>>Question 3: Does this mean that the particles the Earth encounters
 during the Geminid maximum are smaller than the ones that enter Earth's
 atmosphere after maximum? - If so:<<

As stated that's what it would mean. But I think the timing is off in this
statement. The earth probably would encounter a cloud of smaller particles
prior to entering the area with larger material due to a sorting effect from
solar wind.  But I think right at maximum you will find the largest or
brightest meteors for a period of about 2 days than you would find after the
broad two day peak. 
 
 bernd>>Question 4: Does that mean that the Earth and the Geminid meteors meet
 at exactly the same time each year in spite of possible perturbations by
 other planetary bodies?<<

They will meet at the same solar longitude which corresponds to near the same
day...don't forget to take into consideration of leap year. If you knew the
peak hour (UT) for a meteor shower for one year, you can add roughly 6 hours
to it to find a good approximate predicted peak hour for next year. 
 George Zay