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Re: (meteorobs) Are the geminids really disappearing?

In a message dated 12/12/01 4:53:30 PM Eastern Standard Time, 
kikosideral@yahoo.com.br writes:

<< I have an old Astronomy issue (dec/90) that carries an article advising:
 "Observe the geminids before they disappear" (by Phillp Bagnall). Some
 excerpts say:
 
 "The geminid swarm has difted past Earth over the last 150 years. Today
 our orbit still intersects the densest part of the meteor swarm, but by
 the early 21st we will miss this core entirely. The way the shower has
 picked has also changed over the years, with today's shower rising
 slowly to maximum and dropping off sharply"... "This situation is
 exactly the opposite of that witnessed during the 1930's"... "If the
 computer model is correct, we will miss the core completely by the turn
 of the century and rates will plummet."
 
 Have there been any changes to this model since 1990?
 
 Are the geminids ZHR really dropping off in the last few years?
 
  >>
    In Gary Kronk's indispensable "Meteor Showers/A Descriptive Catalog" you 
might partially find the answer to your question.  It seems that a Czech 
astronomer by the name of Miroslav Plavec investigated the orbit of the 
Geminid stream back in 1950.  The most interesting part of his study was 
determining the intersection point between the stream's orbit and the 
ecliptic.  For the year 1700 it was found that the intersection point was 
placed 0.1337 AU inside the Earth's orbit.  For 1900, the intersection point 
was located 0.0178 AU inside the Earth's orbit, while in 2100, the point 
would be 0.1066 AU outside of Earth's orbit.  

    As Gary noted: "Thus, Plavec not only showed why the activity of the 
Geminids was steadily increasing, but he also demonstrated that the activity 
would eventually decline and that sometime in the future Earth would no 
longer contact the stream's orbit."

    As for Phillip Bagnall's reasoning for calling for Geminid rates to 
plummet at the turn of the century, I can only guess that he was 
interpolating from Plavec's findings: 

    Since the first observations of Geminid activity did not occur until 
1862, by simple interpolation from Plavec's numbers we find that the Geminid 
stream was positioned roughly 0.040 AU inside Earth's orbit at that 
particular time. If you were to continue to extrapolate, then the Earth and 
the Geminid orbit would have nearly coincided by the late 1920's and would 
again be roughly 0.040 AU from Earth's orbit (but outside of it) by about the 
end of the 20th century.  Thus, going by these numbers alone, one would have 
every reason to suspect that a significant downturn in Geminid activity would 
be occurring about now.

    However . . . if for nothing else, Geminid activity has actually become 
stronger, with rates increasing from ~50/hr. in the 1950s to the current 
~100/hr.  If we are currently experiencing the absolute peak of the Geminids 
at this point in history, one would like to hope that their "impending 
demise" will be somewhat delayed. 

    Although as rapid has been their increase over the past half century, 
perhaps an even more rapid decline may be about to set in during the next 
half century. Who can say for sure?  We can only take advantage of the fact 
that . . . for this moment in time . . . we can all enjoy a strong and 
reliable annual meteor shower that is rich in bright meteors!

-- joe rao      

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