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Re: (meteorobs) Re: Train, Trail and Wake Definitions by Dr. Jiri Borovicka


----- Original Message -----
From: <SidFerreira@aol.com>
Subject: (meteorobs) Re: Train, Trail and Wake Definitions by Dr. Jiri
Borovicka


.
   In regard to Short Duration Trains, your quote from that definitive
report
stated: "The luminosity is produced (very probably) by the atmospheric
oxygen."Could this luminosity be more easily viewed in areas with gentle
higher alt wind and little or no surface wind?Some of the Longer Persistent
Trains I've seen are visible through binoculars as tubular shaped remnants
even a minute after being created.Most notably,the few North Apex meteors
I've observed over the past few nights have had such lingering remnants and
the air has been very still=======================================
Sidney Ferreira

Sid:
    You must remember that meteoroids enter the earths atmosphere at very
high altitudes becoming visible as a meteor when ablation takes place.  The
atmospheric conditions that you mentioned above, are low altitude
phenomenon.  Cometary meteoroids like the Perseids for example start to be
visible at around 110 kms and burn out at around 80 kms.  At these high
altitudes the atmosphere is very thin, but winds do exist that will distort
a long duration meteor train.  You would not observe this effect by
observing the O I oxygen green line at 557.7 nm as this is a short duration
feature lasting around one second.  This line was first identified by
Canadian meteor astronomer, Dr. Ian Halliday in 1958.  The oxygen green line
appears about 10 km higher than other features in a meteor spectrum.  You
can see an example of this line by going to the AMS web page
(http://www.amsmeteors.org/spectra/majdenobs.html) and looking at the image
intensified video spectrum.  The O I oxygen line is the bright line that is
trailing the main spectrum.  For this line to be present the meteoroid must
be travelling at 40 km/sec or faster.  The mean height of maximum intensity
of this feature is 106 km according to Peter Millman.
    I should note that astronomical nomenclature is very important so
everyone is certain of what is being talked about in scientific papers and
discussions.  The IAU has a nomenclature committee that selects the
definitions that are the accepted standard.

Ed Majden


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