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(meteorobs) Re: Green meteors

    I enjoyed reading Jim Bedients comments and useful references about
meteor colors.  This is indeed a complex topic and controlled study of this
might produce interesting information.  Meteor spectra have been obtained in
a spectral region from around 350.0 nm, near UV to 900.0 nm, near IR.  With
normal non extended red sensitive film, the region covered is from around
350.0 nm to 650.nm.  The eyes peak sensitivity centers on 550 nm or the
green region of the spectrum.
    It is difficult to say how much a dominant spectral line contributes to
the visual color of the meteor.  The path of the meteor is a blend of all
the lines present in the spectrum.  If the H & K lines of Ca+ at the blue
end of the spectrum are the brightest lines recorded, the adding up of the
other lines present will often be brighter than the Ca+ lines alone.  The
resulting color is a combination of all of the lines.  I question even this!
High velocity meteors such as the Perseids often record a strong neutral
oxygen line at 557.7 nm.  This line is sometimes refered to as the forbidden
auroral green line.  This line appears somewhat higher than the main
spectrum and is often present by itself, or at least part of it is, and the
color of the upper end of it is not confused by the blending of the other
features measured in the spectrum.  It is also a persisent radiation lasting
as long as 1 second.  If the color of the meteor is only dependent on the
color of the spectral line, then such a meteor should start out yellow/green
and then change to the color of all the blended features.  I have never seen
this, have any of you?
    I understand that an IMO group is experimenting with photographing the
same meteor through different filters to see if the color index of the
meteor can be determind.  It will be interesting to see the results they
come up with.  I would also suggest using a high speed chopping shutter,
just above the film, so the meteor is chopped up into nearly point sources.
Each point could be measured to see if the color index changes along the
path of the meteor.  Any comments about the color of meteors by
professionals would be of interest to meteorobs readers.  Let's have some
comments from them!

Ed Majden

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