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Re: (meteorobs) Leonids - colors?

Stephen Kaplan wrote

----- Original Message -----
From: Stephen Kaplan <SKaplan@Lakesideglobal.com>

> I'm a "newbie", so kindly excuse these questions if they are off base.
> Even though the duration is so short, does the temperature of the meteor
> change as it advances?  If so, can this have an affect on the color we
see.
>
> What led to this question was another example of  naturally occurring
color
> changes.  Several years ago I visited Yellowstone National Park.  One of
the
> many curiousities concerned the thermal pools.  Water temperatures are
near
> boiling, yet bacteria survive.  The rim of the pool is yellow and the
small
> stream flowing from the pool has varying colorations.  The further the
> stream advances from the pool, the more it cools.  The color of the
bacteria
> changes (mostly in a matter of a few feet) with the water temperature;
> starting with yellow, then orange, red, brown, and finally black.
Different
> color bacteria live exclusively in different water temperatures.
>

    The colour emissions of a meteor are not the same as heating up a piece
of iron with a blow torch where it goes through colour changes from red to
white as the temperature increases.  Meteors produce emission lines in a
spectral range from around 350.0 nm (near ultra violet) to around 900.0 nm
(near IR or red end).  Light is emitted when an electron suddenly changes
from a higher energy level orbit to a lower energy level orbit.  What colour
this ends up as, depends on the element involved.  For example, the H and K
lines of Ca II are strongest in the blue-violet, Na I or Mg I is strongest,
either in the orange-green or blue-violet, and Si II or N+ emits light in
the red around 630.0 nm.  A good physics text book will explain this process
much better than I can.  As stated in my previous message the color of a
fast meteor can shift from at the beginning of the path from red to blue
violet at the end but this is due to the general tendency for the excitation
and ionizatioin level to build up along the path.  Dr Jiri Borovicka from
the Astronomical Institute at Ondrejov Observatory has developed a two
temperature model for fireball spectra.  The temperature of the main
spectrum is about 4000 K and that of the second spectrum is about 10,000 K
which occurs in the head spectrum.  All this is very complex but if you want
to read more, see Borovicka's paper, "Two components in meteor Spectra",
published in Planet. Space Sci., Vol. 42, No. 2, pp. 145-150, 1994.  A good
science library at a university may have this publication.  As stated, this
is all very complex and not all is yet understood about the physics taking
place when this occurs.

Ed Majden - AMS Meteor Spectroscopy Project Coordinator

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