Date: Wed, 16 Oct 2002 13:31:19 -0600

Author: Jerry DiMarco

Subject: Re: Candles and Celestial Spheres

Post:

At 11:22 AM10/15/2002, you wrote:

>1. Is the light from a candle flame only from the blackbody emission
>spectrum? Thus, is the blue part of the flame hotter than the yellow
>part? (or as a faculty member stumped me-- Is this part of the flame
>really hotter than our Sun?) Or is there a contribution from emission
>spectra from electron transitions within given types of atoms? Flame
>viewed through a spectroscope with the eye appears to be a continuous
>spectrum. I know that you can use light emission/absorption to
>fingerprint salts held in the flame, but we're trying to figure out the
>optical properties of the original flame first.

This is an interesting question I haven't thought about very
much. But I do know the temperature of a candle flame is well
documented. The following webpage says it is 1400 C for the blue part and
800 C for the yellow part. http://webexhibits.org/causesofcolor/3B.html
That seems to be in the ballpark as compared to previous experience. That
page also has an interesting photo of a candle flame in zero gravity.
The colors in a flame must be due to spectral lines since the above
temperatures are not enough to cause even a faint blackbody glow in the
visible part of the spectrum. I don't know all the elements involved in
combustion but hydrocarbons are rich in carbon, and the standard spectrum
wall chart shows that the spectral lines for carbon (C2) are at the blue
end. There is a nice webpage showing spectra of several more elements at:
http://home.achilles.net/~jtalbot/data/elements/index.html

>2. Our intro astronomy prof would like a 'celestial sphere' that
>surrounds an Earth globe. We're looking for something of 0.5-1.0 m
>diameter that could be used in the classroom to show the tilt of the
>Earth's axis and the positions of stars above. Any suggestions for
>quality sources of this at reasonable prices?

We have a large (~1/2 m) celestial sphere which I thought we
purchased from MMI Corp (mmicorporation.com) but I couldn't find the
record. However, the other big catalog suppliers have them too...

Jerry


>Thanks again!
>
>bill
>
>--
>*****************************************
>William W. McNairy, Ph. D.
>Lecturer
>Room 104I (919)-660-2689
>Dept. of Physics, Duke University
>Box 90305 Durham, NC 27708
>*****************************************


<><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

Jerry DiMarco
Manager of Lecture Demonstrations and Instructional Labs
Montana State Univ., Physics Dept.
Bozeman, MT

Our Motto: "We don't use anything the way it was meant to be used."

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