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Re: (meteorobs) Re: Excerpts from "CCNet 97/2000 - 28 September 2000"



Phil--

John Lewis and Jim Oberg are correct for LARGE objects. However, for most
(smaller) meteoroids where the atmospheric mean free path is larger than the
characteristic size of the body no air cap forms as the flow is free molecular
(as opposed to continuum). In this case individual air molecules may collide
with the meteoroid, casuing sputtering and ablation. Most of the light
emission is due to excitation (and some ionization) of liberated meteoric
atoms in collision with air molecules.
See

Meteor Phenomena and Bodies
 Authors:

                   Ceplecha, Zdene , K.; Borovicka, Jir , Í.; Elford, W.
Graham; Revelle, Douglas O.; Hawkes, Robert L.; Porubcan, Vladimír; Simek,
Milos
 Affiliation:

                   AA(Ondrejov Observatory, Astronomical Insitute, Academy of
Sciences, Czech Republic), AB(Ondrejov Observatory, Astronomical Insitute,
Academy of
                   Sciences, Czech Republic), AC(Department of Physics and
Mathematical Physics, University of Adelaide, Australia), AD(Los Alamos
National Laboratories,
                   U.S.A.), AE(Department of Physics, Engineering, and
Geology, Mount Allison University, Sackville, Canada), AF(Astronomical
Institute, Slovak Academy of
                   Sciences, Slovakia), AG(Ondrejov Observatory, Astronomical
Insitute, Academy of Sciences, Czech Republic)
 Journal:

                   Space Science Reviews, v. 84, Issue 3/4, p. 327-471 (1998).
(SSRv Homepage)

Regards,
Peter

"Phil Plait (via Lew Gramer)" wrote:

> Hello--
>
> My comment on CCNet about compressional heating is what I determined after
> a lengthy talk with John Lewis as well as reading Opik and a few other
> texts. Oberg's comments are basically correct; also, meteorites tend to
> have ablated material cooled and hardened on their 'back' side, indicating
> a relatively low amount of friction with oncoming air.
>
> If anyone has more, I'd love to hear it. Dispensing astronomy myths
> is literally my business! ;-)
>
> - -Phil Plait
>
> *    *    *    *    *    The Bad Astronomer    *    *    *    *
>
> Phil Plait                    badastro@badastronomy.com
> The Bad Astronomy Web Page: http://www.badastronomy.com
>
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--
*********************************************************************
Dr. Peter Brown
Assistant Professor
Meteor Physics Group
Department of Physics and Astronomy
University of Western Ontario
London, Ontario
N6A 3K7
Canada

http://phobos.astro.uwodot ca/~pbrown
Voice:1-519-661-2111 x86458
Fax:1-519-661-4085
email:pbrown@julian.uwodot ca
Meteor Astronomy Lab : 1-519-661-2111 x84744
Meteor Physics Lab :   1-519-850-2385
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