Heliochromology: Agreed terms help sensible discussion

Jun 1, 2020
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Well perhaps this will serve this highly limited, but colorful, subject. :)

Heliochromology - The study to determine the Sun's color. It studies the many objective lines of evidence to determine its "true color" -- as would be visually observed in space and attenuated to a comfortable level to accommodate the eye's photopic vision range.

The majority of the public, and in the recent past, even science forum members, favored the view that the Sun is actually a yellow-white star. A fewer number assume a varying range of colors for the Sun.

The Sun's true color, however, is demonstrably not yellow, not even with a hint of a tint.

History:
Within astronomy, the Sun is known as a yellow dwarf G2V class star. The yellow color term was originally used by the early pioneers of stellar spectroscopy. The "Father of spectral spectroscopy", Fr. Angelo Secchi, introduced four (three originally) major star types based on their spectrum. The Sun, in his determination, was a close spectral match to Capella, known to have a yellow tint, so the Sun was categorized into the yellow type of stars.

Interestingly, todays system is far more advanced. It came from the remarkable work from astronomers, especially, Annie Jump Cannon, who classified over 200,000 stars. Yet all of these classifications were from black and white spectrums, thus without much color consideration.

Since the Sun often appears yellow during sunsets -- it is too bright to determine its color directly --the yellow color view likely reinforced any idea that the Sun actually is yellow.

Further, other yellow-color reinforcement may have come from things like our use of Crayolas when, on white paper, the Sun was colored commonly with the yellow crayon.

More importantly, perhaps, is the ubiquitous coloring of the Sun in publications and textbooks. It is extremely rare to see it depicted as white.

Determination:
There are multiple lines of evidence that favor a white-only Sun. [All these are terrestrial views.] These include:

1) The bright white seen from the reflection of sunlight off snow. [Depending on flakes sizes, up to ~ 98% of the reflection is an even distribution of its spectral colors. ]

2) Clouds are white (Mie Scattering), which also reflects evenly.

3) Pin-hole projection and other accurate color projections of a noon-time Sun present no evidence for yellow as a tint.

4) A photon flux distribution demonstrates that the colors are very evenly distributed. [The common spectral irradiance distributions show the Sun, from space, has a strong peak in the blue portion of the spectrum, but there are almost 1/2 as many "blue" photons, for example, than there are "red" photons since more energy is required for the shorter wavelength photons.]

5) Adjusting the terrestrial spectral irradiance of the Sun to match its spectral irradiance as seen in space (i.e. AM0), will result in a white-only result (by hypothesis).

6) The McMath-Pierce solar observatory's projection (unfiltered) of the Sun presents an all white image, from limb to center. Since (via Rayleigh Scattering) the atmosphere removes far more of the shorter wavelengths (e.g. blue colors) than the other wavelengths, then to match what would be seen in space one would need to add more of the blue-end colors to the white result. Yet, adding a little more blue could never produce a yellow result for the Sun's disk, even along the limb of the Sun, which has a much lower temperature. Hence, the Sun's true color has not hint of yellow.

All evidence so far favors that the Sun is an all-white (colorless) star.

Seen from space, astronauts have mentioned that it is bright white. But when the color cones of the eye encounter intensities exceeding its upper threshold limit, a white result is the result if all the colors exceed this threshold. Thus, even if one color was greater than the others, the eye-brain (retinex) would fail to recognize a color, assuming the intensity was properly attenuated.
 
Last edited:
Dec 9, 2020
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An informative article; thanks. As I recall using Wien's Law and the Sun's surface temperature of 5800K, our Sun should have a green tint, but that calculation is an approximation and our atmosphere scatters out lower wave length light, thus a yellow Sun is what we get on Earth which is a pleasant, non-offensive color especially on gifting days in the form of jewelry.
 
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Jul 4, 2021
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Well perhaps this will serve this highly limited, but colorful, subject. :)

Heliochromology - The study to determine the Sun's color. It studies the many objective lines of evidence to determine its "true color" -- as would be visually observed in space and attenuated to a comfortable level to accommodate the eye's photopic vision range.

The majority of the public, and in the recent past, even science forum members, favored the view that the Sun is actually a yellow-white star. A fewer number assume a varying range of colors for the Sun.

The Sun's true color, however, is demonstrably not yellow, not even with a hint of a tint.

History:
Within astronomy, the Sun is known as a yellow dwarf G2V class star. The yellow color term was originally used by the early pioneers of stellar spectroscopy. The "Father of spectral spectroscopy", Fr. Angelo Secchi, introduced four (three originally) major star types based on their spectrum. The Sun, in his determination, was a close spectral match to Capella, known to have a yellow tint, so the Sun was categorized into the yellow type of stars.

Interestingly, todays system is far more advanced. It came from the remarkable work from astronomers, especially, Annie Jump Cannon, who classified over 200,000 stars. Yet all of these classifications were from black and white spectrums, thus without much color consideration.

Since the Sun often appears yellow during sunsets -- it is too bright to determine its color directly --the yellow color view likely reinforced any idea that the Sun actually is yellow.

Further, other yellow-color reinforcement may have come from things like our use of Crayolas when, on white paper, the Sun was colored commonly with the yellow crayon.

More importantly, perhaps, is the ubiquitous coloring of the Sun in publications and textbooks. It is extremely rare to see it depicted as white.

Determination:
There are multiple lines of evidence that favor a white-only Sun. [All these are terrestrial views.] These include:

1) The bright white seen from the reflection of sunlight off snow. [Depending on flakes sizes, up to ~ 98% of the reflection is an even distribution of its spectral colors. ]

2) Clouds are white (Mie Scattering), which also reflects evenly.

3) Pin-hole projection and other accurate color projections of a noon-time Sun present no evidence for yellow as a tint.

4) A photon flux distribution demonstrates that the colors are very evenly distributed. [The common spectral irradiance distributions show the Sun, from space, has a strong peak in the blue portion of the spectrum, but there are almost 1/2 as many "blue" photons, for example, than there are "red" photons since more energy is required for the shorter wavelength photons.]

5) Adjusting the terrestrial spectral irradiance of the Sun to match its spectral irradiance as seen in space (i.e. AM0), will result in a white-only result (by hypothesis).

6) The McMath-Pierce solar observatory's projection (unfiltered) of the Sun presents an all white image, from limb to center. Since (via Rayleigh Scattering) the atmosphere removes far more of the shorter wavelengths (e.g. blue colors) than the other wavelengths, then to match what would be seen in space one would need to add more of the blue-end colors to the white result. Yet, adding a little more blue could never produce a yellow result for the Sun's disk, even along the limb of the Sun, which has a much lower temperature. Hence, the Sun's true color has not hint of yellow.

All evidence so far favors that the Sun is an all-white (colorless) star.

Seen from space, astronauts have mentioned that it is bright white. But when the color cones of the eye encounter intensities exceeding its upper threshold limit, a white result is the result if all the colors exceed this threshold. Thus, even if one color was greater than the others, the eye-brain (retinex) would fail to recognize a color, assuming the intensity was properly attenuated.
Is the sun's chromosphere useful when determining the sun's color during a total eclipse?
 

Catastrophe

The devil is in the detail
Sorry, I get carried away sometimes.
No problem. :) :) :)
Before Helio arrives, I found this for a start:
"The chromosphere ("sphere of color") is the second of the three main layers in the Sun's atmosphere and is roughly 3,000 to 5,000 kilometers deep. Its rosy red color is only apparent during eclipses. The chromosphere sits just above the photosphere and below the solar transition region."
 
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