[AZ-Observing] Re: Meteor Colors

  • From: "Dan Heim" <dan@xxxxxxxxxxxxx>
  • To: <az-observing@xxxxxxxxxxxxx>
  • Date: Fri, 30 Jan 2009 09:20:32 -0700

The color most often seen comes predominately from the ionization of gases
in the upper atmosphere, which is mostly nitrogen.  Hence the typical
light-bluish-violet streaks of small, short, quick, meteors.  Same color as
lightning, or the electric spark you see when static electricity jumps from
your finger to a light switch.  How much energy does this take?  For that
molecule (N2) the energy required for ionization is 14.5 eV (or,
alternatively, 1402 kJ/mole).

Consider a "typical" visible meteor, about the size of a BB.  It has a mass
of, say, half a gram, depending on composition.  It's speed is, say, 15
km/s.  That gives it a kinetic energy on the order of 50,000 joules.  That's
sufficient to ionize a 20-30 moles of nitrogen via direct collision, in a
small channel about the diameter of a BB but very long.  How long is tough
to calculate, since the standard we all learned in chemistry (22.4
liters/mole) applies at STP, and the upper atmosphere is not at STP.  In
fact, the meteor penetrates through a large range of altitudes within which
pressure and temperature vary continuously, so it becomes a calculus
problem, and I didn't feel like doing any calculus this morning.  :)  Of
course, we all know that "typical" meteor trails can be a few 10s of
kilometers long.

So you can think of this "light-bluish-violet" as the base color ... it will
always be there.  Sometimes though, other colors are superimposed over that
due to ionization of the meteor itself.  Recall the "flame test" from
chemistry class, wherein different elements held in the flame of a bunsen
burner produced various colors.  Sodium = yellow, strontium = red, etc.
Meteors that are high in one specific elemental content, have a rougher
surface, or enter at a specific speed or angle, may produce sufficient
additional colors to overwhelm the base color of nitrogen.  Some swarms are
known to preferentially produce this effect, for example, the Leonids are
often described as "yellow."  In general though, only the "larger" ones will
be able to provide sufficient ablated material to overwhelm the color of
ionized nitrogen.  By "larger" I mean the size of peanuts to walnuts.  And
the larger they are, the longer the trail, and, in general, the slower the
average speed.

And that's why most meteors are the same light-bluish-violet color, at least
to the naked eye.  But a spectrometer would always see a few other colors in
there.

Dan Heim
President
Desert Foothills Astronomy Club
http://www.dfacaz.org




----- Original Message ----- 
From: "Keith Parizek" <keithparizek@xxxxxxx>
To: <az-observing@xxxxxxxxxxxxx>
Sent: Friday, January 30, 2009 6:14 AM
Subject: [AZ-Observing] Re: Meteor Colors


> Hi Dan- When a meteor enters our atmosphere where does the color come
from?
> Does it all come from the friction burning of the meteor mass itself or
does
> the meteor passing thru our upper atmosphere ionize the atmosphere?  Maybe
> some of both.  What energy or force does it take to ionize the atmosphere?
>
> Regards
> Keith Parizek
> ----- Original Message ----- 
> From: "Dan Heim" <dan@xxxxxxxxxxxxx>
> To: <az-observing@xxxxxxxxxxxxx>
> Sent: Thursday, January 29, 2009 9:42 PM
> Subject: [AZ-Observing] Re: Meteor Colors
>
>
> Way back in the early 80s, shortly after I moved to PHX, there was a great
> Perseid shower.  It was during that shower when I saw my first (there was
> another many years later) "skipping" meteor.  It came in nearly parallel
to
> the north horizon, growing brighter slowly, then curved up and got dimmer,
> then it came down again and increased in brightness a final time before
> extinction.  The trajectory veered up and down by no more than 5°.  The
> color was orange to red, and, to corroborate AJ's comment, it was a slow
> meteor.
>
> Dan Heim
> President
> Desert Foothills Astronomy Club
> http://www.dfacaz.org
>
> ----- Original Message ----- 
> From: "AJ Crayon" <acrayon@xxxxxxx>
> To: <az-observing@xxxxxxxxxxxxx>
> Sent: Thursday, January 29, 2009 8:45 PM
> Subject: [AZ-Observing] Re: Meteor Colors
>
>
> > From a web search the following, short versions, were found -
> >     slow meteors can be seen as red or orange
> >     silicon atoms and molecules of atmospheric nitrogen give a red light
> >     silicate meteors produce fiery red colors
> >
> > There's lots more out there about this topic.
> >
> > AJ Crayon
> > Phoenix, AZ
> >
> > ----- Original Message ----- 
> > From: "Jimmy Ray" <jimmy_ray@xxxxxxx>
> > To: <az-observing@xxxxxxxxxxxxx>
> > Sent: Thursday, January 29, 2009 8:23 PM
> > Subject: [AZ-Observing] Meteor Colors
> >
> >
> > To All,
> >
> > Happened to be outside at 00:45 Hours this morning looking out to the
SSW
> > when a small, fast meteor streaked east to west in the area of Canis
> Minor.
> > It left a momentarily persistent trail and was gone. It would have
> normally
> > been rather unmemorable except the color, which was an a dark
orange-red,
> > which was a first for me. The sky seemed clear (no perceptible smoke or
> > such) and was about 45 degrees above the horizon. I have seen plenty of
> > Green, blue, and white ones, exploding ones and even a "head on" one but
> > orange-red? Any thoughts?
> >
> > Jimmy Ray
> >
> > --
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> >
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> >
>
>
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