Sun Emission Spectrum: Redshift/Blueshift & Visible Light

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Discussion Overview

The discussion centers around the nature of the Sun's emission spectrum, specifically addressing whether the continuous spectrum observed is a result of redshift and blueshift effects, or if it is primarily due to other mechanisms such as thermal motion and atomic collisions. The scope includes theoretical explanations and conceptual clarifications regarding light emission processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions if the continuous spectrum of the Sun is due to redshift/blueshift of radiation, noting the quantized nature of hydrogen's emission spectrum.
  • Another participant explains that light can be produced through various mechanisms, including atomic collisions, which contribute to a wide spectrum of radiation at a given temperature.
  • A participant suggests that the Sun can be treated as a blackbody, emitting radiation according to the blackbody spectrum, while also acknowledging the presence of spectral lines.
  • Data from NIST is referenced, indicating specific intensities of solar hydrogen spectral lines and discussing how the motion of hydrogen atoms affects the observed photon energies through redshift and blueshift.
  • One participant argues against the idea that redshift/blueshift explains the continuous spectrum, asserting that Doppler broadening is insufficient and that thermal motion is the primary source of photon production.
  • A later reply acknowledges the correction regarding the importance of thermal motion in producing the spectrum.

Areas of Agreement / Disagreement

Participants express differing views on the role of redshift/blueshift in the Sun's emission spectrum, with some emphasizing the significance of thermal motion and atomic collisions, while others initially propose redshift/blueshift as a contributing factor. The discussion remains unresolved regarding the extent to which each factor contributes to the observed spectrum.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the mechanisms of light production and the definitions of terms like "continuous spectrum." The mathematical details of the spectral lines and their broadening effects are not fully explored.

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Is the rather continuous spectrum of the Sun due to redshift/blueshift of the radiation emenating from the Sun? I understand that the emission spectrum of Hydrogen in the visible range is quantized to four discrete values, but I'm trying to understand how all frequencies of visible light are available for us to use.
 
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Light is produced in many ways besides the excitation of individual atomic spectral lines. For example it can be produced when atoms collide. Quoting Wikipedia,

When the temperature of the body is greater than absolute zero, interatomic collisions cause the kinetic energy of the atoms or molecules to change. This results in charge-acceleration and/or dipole oscillation which produces electromagnetic radiation, and the wide spectrum of radiation reflects the wide spectrum of energies and accelerations that occur even at a single temperature.
 
The sun can be treated as a blackbody ... it is a very hot body, and thus emits radiation following the blackbody spectrum.

You can see definite lines in the solar spectrum; these are well explained here:
http://www.astro.washington.edu/courses/labs/clearinghouse/labs/Solarspec2/sunspec.html
 
Last edited by a moderator:
NIST data (http://www.nist.gov/pml/data/asd.cfm) give Solar Hydrogen Spectral Lines intensity in terms of energy: 250,000@12.09eV, 840,000@10.20eV, 90,000@2.86eV, 180,000@2.55, 500,000@1.89eV. The 1.89 eVolt energy is the most common one we can see.

We see all sorts of other photon energies that are generated since the hydrogen on the sun surface is moving around. If the hydrogen atom is moving away from us, we will see a photon with less than 1.89eV (red shifted), if moving towards us, it will have more than 1.89eV energy (blue shifted)
 
edguy99 said:
We see all sorts of other photon energies that are generated since the hydrogen on the sun surface is moving around. If the hydrogen atom is moving away from us, we will see a photon with less than 1.89eV (red shifted), if moving towards us, it will have more than 1.89eV energy (blue shifted)
No. As pointed out above, this is absolutely not the explanation. Doppler broadening of the spectral lines is present, but much too small to produce a continuous spectrum. And the majority of the photons are produced in other ways, simply from the thermal motion of the atoms.
 
Last edited:
Bill_K said:
... much too small to produce a continuous spectrum. And the majority of the photons are produced in other ways, simply from the thermal motion of the atoms.

Thank you for the correction, I agree the thermal motion is the most important.
 

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