What Causes Distinct Absorption Bands in the Sun's Spectrum During Sunset?

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    Absorption Atmospheric
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Discussion Overview

The discussion centers around the distinct absorption bands observed in the spectrum of the setting Sun, particularly in the yellow and orange regions. Participants explore potential causes for these bands, considering factors such as atmospheric conditions and pollutants, while also discussing the limitations of their observational equipment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes the observation of distinct absorption bands in the yellow/orange region of the Sun's spectrum during sunset, questioning their origin.
  • Another participant inquires about the number of bands visible and suggests they may not be sodium lines from the Sun.
  • A participant expresses doubt about the resolution of their spectroscope being sufficient to detect absorption lines, while also noting the absence of obvious candidates among common pollutants.
  • One participant humorously suggests shaking the spectroscope to ensure its accuracy, implying skepticism about the equipment's reliability.
  • Another participant speculates that the observed bands may relate to a brown spectrum, suggesting a connection to specific pigments or pollutants.

Areas of Agreement / Disagreement

Participants express varying degrees of skepticism about the observations and the capabilities of the spectroscope, but there is no consensus on the cause of the absorption bands or their significance. Multiple competing views and hypotheses remain unresolved.

Contextual Notes

The discussion highlights limitations related to the observational equipment's resolution and the potential influence of local atmospheric conditions, such as pollution, on the observed spectrum.

sophiecentaur
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I recently bought a cheap and cheerful hand held spectroscope. Great fun to look at CFL lamps and the modern LEDs. Those LEDs are really good, btw. Also, the 'scope gives a pretty even spread of brightness over the whole visible range. (an equipment check).
I have been looking at the spectrum of the setting Sun on a regular basis. I see distinct absorption bands in the yellow / orange region. Blue is a bit attenuated, perhaps and red is continuous again. I would like to know what the bands are due to. I am looking at the Sun, low over the London conurbation and I suspect it could be something to do with that.
Any ideas?
I must remember to take the scope with me next time I can see a sunset over a clean horizon. Does that justify a short break in Cornwall??
 
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sophiecentaur said:
I see distinct absorption bands in the yellow / orange region.

How many bands can you see? I assume they aren't the sodium lines from the Sun itself?
 
Drakkith said:
How many bands can you see? I assume they aren't the sodium lines from the Sun itself?
A question worth asking but the clean solar spectrum is line-free in my scope. I would doubt that the scope resolution would be good enough to spot an absorption line, in any case.
I have been looking at absorption bands from common pollutants and there don't seem to be any obvious candidates. There is much more info on IR absorption, which is what most of the google hits contain.
My observations are very qualitative but I would say that there is a region (say 550 nm to 580nm [Edit Correction- to a bit over 600nm]) where there seem to be two or three ragged bands of dark and the whole of the spectrum there is much dimmer. My eyes and the scope behave themselves fine for the rest of the day. (just been outside and checked again).
 
sophiecentaur said:
A question worth asking but the clean solar spectrum is line-free in my scope. I would doubt that the scope resolution would be good enough to spot an absorption line, in any case.

To be safe, I'd give your scope a good shake or two to make sure it isn't lying to you. Let it know you mean business and all that.
 
It would need to be far too intelligent to know just when to play up and when not to! I reckon what I am seeing is genuine but it doesn't seem to fit anything I have read about so far. Perhaps there is a cloud of BS over London?
 
Brown spectrum( from an M&M coating) matches your description. I think you are definitely on to something. Try your spectroscope over Parliament ! If it matches bilirubin (brown pigment in feces) spectrum you have proof positive.

http://www.trinity.edu/fwalmsle/MandMPictures/BrownSolutionSpectrum.bmp
 

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