The whole issue of meteor color is complex. We now have many examples of
high resolution meteor spectra... but "color" is a physiological
phenomenon that isn't always easy to relate to physical spectra.
The light of meteors consists mostly of thermally broadened atomic
emission lines- lots of them- from both the meteoritic material and the
atmosphere. As has been noted, the atmospheric contributions tend to
dominate. But there are often strong lines from meteoritic material, as
well. In the case of large fireballs (where we have much less
spectroscopic data) there may be a blackbody contribution as well,
either from the ablating surface or from a supercompressed plasma. And
since this is mostly driven by thermal effects, the speed of the body
makes a big difference in perceived color. Throw into all of this the
complexities of human vision- differences in retinal response,
persistence effects, psychological effects given typically short
observation times- and it's little wonder this entire area remains
poorly understood.
After large fireballs, when I get many witness reports submitted, I
review color. It's common for about half the witnesses who report color
to agree on one in particular (green is by far the most common), while
the other half see red, orange, yellow, or blue.
My takeaway is that we should generally assume that most color is coming
from atmospheric contributions, probably modified slightly by meteoritic
components (often too subtly for people to report accurately), and that
above all, it's almost impossible to make any assumptions about
meteoroid composition from color.
Chris
*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
On 11/4/2015 5:21 AM, Beatty, Kelly via Meteorite-list wrote:
Marco, Rob...
this discussion is timely. what you've noted is exactly my understanding. just
yesterday I came across a high-profile blog about these fireballs, and the
writer stated that most of the light comes from the superheated vaporized
particle as it ablates. suspecting this was wrong, I looked in several places
for the correct information -- IMO, AMS, RASC Handbook, etc -- and yet I didn't
really find the physics spelled out explicitly. (maybe I was looking in the
wrong places?) the closest I came was this post by Peter Jenniskens
(http://leonid.arc.nasa.gov/meteor.html), which was equivocal.
clear skies,
Kelly
*******************************
J. Kelly Beatty
Senior Editor, Sky & Telescope
SkyandTelescope.com
(a division of F+W, a Content + eCommerce Company)
617-864-7360 x22168
@NightSkyGuy
-----Original Message-----
From: Meteorite-list [mailto:[email protected]] On
Behalf Of Rob Matson via Meteorite-list
Sent: Wednesday, November 04, 2015 3:54 AM
To: 'meteorite-list'
Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween
Night
HI All,
Marco took the words out of my mouth. Getting tired of hearing that a green
meteor tells you anything about its composition. I know that it's natural for
people to think the most important thing they can report about a meteor is its
color, but I wish various broadcast media would do the public a service and
disabuse them of this notion. It would be far better if witnesses could be
trained to get in the habit of counting the duration accurately, and noting the
exact time of the meteor to the nearest minute. Seeing as how almost everyone
has a cell phone these days, and all cell phones have accurate clocks, there
really is no excuse to get the time wrong. Yet even a casual browse of the AMS
fireball site reveals that people clearly don't think getting the time right is
important. And even more obvious is that most people have no business reporting
anything about fireball starting and ending bearings and elevation angles.
--Rob
-----Original Message-----
From: Meteorite-list [mailto:[email protected]] On
Behalf Of Marco Langbroek via Meteorite-list
Sent: Wednesday, November 04, 2015 12:06 AM
To: [email protected]; [email protected]
Subject: Re: [meteorite-list] Very Bright Fireball Over Europe on Halloween
Night
A lot of folks say it looked green to them, which means it may have
been metallic;
It is a perpetuated misunderstanding that meteor colours are primarily due to
their composition. It's a science myth inspired by High School Bunsen burner
experiments that appears hard to kill.
While composition in some cases does have some influence on the colour, it is
actually the composition of the atmosphere that is usually dominant for our
perception of meteor colours.
That certainly is true for green colours. Meteor spectra show that meteors usually are
very strong at the "forbidden" Oxygen line at 5577 Angstrom (557.7 nm). This
line is due to atmospheric Oxygen, the same atmospheric Oxygen exitation line also
responsible for the green colours of Aurora.
So green meteor colours are likely atmospheric in origin and say little about
the meteoroids' composition.
- Marco
-----
Dr Marco (asteroid 183294) Langbroek
Dutch Meteor Society (DMS)
e-mail: [email protected]
http://www.marcolangbroek.nl
______________________________________________
Visit our Facebook page https://www.facebook.com/meteoritecentral and the
Archives at http://www.meteorite-list-archives.com
Meteorite-list mailing list
[email protected]
https://pairlist3.pair.net/mailman/listinfo/meteorite-list
______________________________________________
Visit our Facebook page https://www.facebook.com/meteoritecentral and the
Archives at http://www.meteorite-list-archives.com
Meteorite-list mailing list
[email protected]
https://pairlist3.pair.net/mailman/listinfo/meteorite-list
______________________________________________
Visit our Facebook page https://www.facebook.com/meteoritecentral and the
Archives at http://www.meteorite-list-archives.com
Meteorite-list mailing list
[email protected]
https://pairlist3.pair.net/mailman/listinfo/meteorite-list
