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Re: Fireball colors?


     To Matt and the List,
     
     The following is extracted from a recent forwarding from Ron Baalke:
     
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     
     >Forwarded from Jim Bedient (wh6ef@pixi.com)
     >Subject: FAQ - Fireballs and Meteorite Dropping Fireballs
     
     >--------------------------------------------------------------------- 
     -
     >The American Meteor Society, Ltd.
     
     >Frequently Asked Questions (FAQ)
     >About Fireballs and Meteorite Dropping Fireballs
     
     >Version 1.2
     
     >Question List:
     ---SNIP!---
     >  5. Can fireballs appear in different colors? 
     ---SNIP!---
     
     >5. Can fireballs appear in different colors?
     
     >Vivid colors are more often reported by fireball observers because 
     >the brightness is great enough to fall well within the range of human 
     >color vision. These must be treated with some caution, however, 
     >because of well-known effects associated with the persistence of 
     >vision. Reported colors range across the spectrum, from red to bright 
     >blue, and (rarely) violet. The dominant composition of a meteoroid 
     >can play an important part in the observed colors of a fireball, with 
     >certain elements displaying signature colors when vaporized. For 
     >example, sodium produces a bright yellow color, nickel shows as 
     >green, and magnesium as blue-white. The
     >velocity of the meteor also plays an important role, since a higher 
     >level of kinetic energy will intensify certain colors compared to 
     >others. Among fainter objects, it seems to be reported that slow 
     >meteors are red or orange, while fast meteors frequently have a blue 
     >color, but for fireballs the situation seems more complex than that, 
     >but perhaps only because of the curiousities of color vision as 
     >mentioned above.
     
     >The difficulties of specifying meteor color arise because meteor >light 
     is dominated by an emission, rather than a continuous, >spectrum. The 
     majority of light from a fireball radiates from a >compact cloud of 
     material immediately surrounding the meteoroid or >closely trailing it. 
     95% of this cloud consists of atoms from the >surrounding atmosphere; the 
     balance consists of atoms of vaporized >elements from the meteoroid 
     itself. These excited particles will emit >light at wavelengths 
     characteristic for each element. The most common >emission lines observed 
     in the visual portion of the spectrum from >ablated material in the 
     fireball head originate from iron >(Fe),magnesium (Mg), and sodium (Na). 
     Silicon (Si) may be >under-represented due to incomplete dissociation of 
     SiO2 molecules. >Manganese (Mn), Chromium (Cr), Copper (Cu) have been 
     observed >infireball spectra, along with rarer elements. The refractory 
     >elements Aluminum (Al), Calcium (Ca), and Titanium (Ti) tend to be 
     >incompletely vaporized and thus also under-represented in
     >fireball spectra.
     
     This passage supports George Zaye's contention that fireball color is 
     dominated by ionized nitrogen as stated in previous postings to this 
     List.
     
     Regards,
     Bob V.
     
______________________________ Reply Separator _________________________________
Subject: Fireball colors?
Author:  mhmeteorites@geocities.com at Internet 
Date:    6/19/98 7:35 AM
     
     
Hi list:
I was talking with Jack Murphy at the Denver Museum yesterday and we 
started discussing the recent fireball activity. He asked me if I could 
correlate fireball color to meteorite type.  I thought about it, but I 
could not answer his question. I assume the color is based on the 
chemical composition of the meteoroid. Does anyone know which 
chemical/chemicals/minerals burn green, blue, or red for instance? 
Thanks,
--
Matt Morgan
Mile High Meteorites
http://www.mhmeteorites.com
P.O.Box 151293
Lakewood, CO 80215-9293
"For a geologist, life is a field trip"