- #1
Cool4Kat
- 45
- 13
So I was taught in school that heated low density gases produce spectral lines and cool low density gases absorb their spectral lines. I mentioned this to my husband and he asked me what the definition of hot and cool were and I had no idea. The more I thought about it, the more confused I became. Sodium that is heated in a lab emits the spectral lines and sodium on the surface of the sun (which is way hotter) absorbs the light. Also, the gasses in the atmosphere don't seem to make absorption lines in sunlight. [Edit: it turns out that the atmosphere can make absorption lines, especially at sunset or sunrise, but doesn't do it very much]
Then, I was studying how Kirchhoff accidentally discovered how spectrum analysis could be used to study the sun. In October of 1859, Kirchhoff was playing with looking at heated sodium with his spectrometer when, as a lark, he tried placing bright lamp light through it as well as the heated sodium. He was expecting a rainbow with brighter yellow doublet, instead the sodium absorbed the doublet, mimicking the sodium shadows in sunlight. So here was an example of a *heated* gas absorbing radiation!
Therefore, I have come to the conclusion that the "cool gasses absorb" statement is not correct. So what is really going on? I have a theory, and I wonder if any of you wise folks can tell me if I am on the right track or totally confused.
Theory: After a certain temperature threshold, low density gasses all emit their spectrum of light. They also, at this temperature, can absorb their spectrum of light. If they are irradiated with external radiation at these frequencies, the transmitted light has that spectrum absorbed because the emitted radiation from the gas is scattered and reflects towards the external radiation source. In Kirchhoff's experiment, the sodium gas acts like a mirror and reflects the yellow doublet back towards the lamp. If he had studied the sodium gas from an other angle the yellow doublet would be brighter as it would contain the light of the sodium and the reflected yellow light from the lamp.
Am I close? Am I full of it? Thank you a million times for your wise counsel.
Kathy
Then, I was studying how Kirchhoff accidentally discovered how spectrum analysis could be used to study the sun. In October of 1859, Kirchhoff was playing with looking at heated sodium with his spectrometer when, as a lark, he tried placing bright lamp light through it as well as the heated sodium. He was expecting a rainbow with brighter yellow doublet, instead the sodium absorbed the doublet, mimicking the sodium shadows in sunlight. So here was an example of a *heated* gas absorbing radiation!
Therefore, I have come to the conclusion that the "cool gasses absorb" statement is not correct. So what is really going on? I have a theory, and I wonder if any of you wise folks can tell me if I am on the right track or totally confused.
Theory: After a certain temperature threshold, low density gasses all emit their spectrum of light. They also, at this temperature, can absorb their spectrum of light. If they are irradiated with external radiation at these frequencies, the transmitted light has that spectrum absorbed because the emitted radiation from the gas is scattered and reflects towards the external radiation source. In Kirchhoff's experiment, the sodium gas acts like a mirror and reflects the yellow doublet back towards the lamp. If he had studied the sodium gas from an other angle the yellow doublet would be brighter as it would contain the light of the sodium and the reflected yellow light from the lamp.
Am I close? Am I full of it? Thank you a million times for your wise counsel.
Kathy
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