APOD: All the Colors of the Sun (2015 Jun 28)

[APOD Robot]

All the Colors of the Sun

Explanation: It is still not known why the Sun's light is missing some colors. Here are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device. The spectrum was created at the McMath-Pierce Solar Observatory and shows, first off, that although our white-appearing Sun emits light of nearly every color, it does indeed appear brightest in yellow-green light. The dark patches in the above spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below. Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun. Helium, for example, was first discovered in 1870 on a solar spectrum and only later found here on Earth. Today, the majority of spectral absorption lines have been identified - but not all.

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[Beecroft]

Apparently the sun supports marriage equality! (With a few colors unrecognized...)

[Slawomir]

I am wondering whether sunlight being predominantly yellow-green has something to do with chlorophyll having green colour as well.

[rj rl]

Why are the missing patches all blurry? I thought the absorption occurs only at very certain wave-lengths and not at wave-length +/- couple nanometers.

[Cousin Ricky]

I am wondering whether sunlight being predominantly yellow-green has something to do with chlorophyll having green colour as well.

It doesn’t. It is not to a plant’s advantage to reflect away the predominant wavelengths of its energy source, so the colors are probably just a coincidence. Most plants have such a low albedo anyway, that the fact that they reflect slightly more green than other wavelengths is of little consequence.

[JohnD]

Agree about chlorophyll, but another coincidence is that the rods (non-colour receptors) of the human eye are most sensitive to light at 498 nanometers, which is only a little bluer than the maximally energetic wavelength of sunlight.
In low light,"Scoptopic" situations, even cats see best the same wavelength. They have the 'tapetum lucidum' reflective layer in the retina to optimise low light vision.
Coincidence? Or evolutionary adaptation?

John

[neufer]

I am wondering whether sunlight being predominantly yellow-green has something to do with chlorophyll having green colour as well.

It doesn’t. It is not to a plant’s advantage to reflect away the predominant wavelengths of its energy source, so the colors are probably just a coincidence. Most plants have such a low albedo anyway, that the fact that they reflect slightly more green than other wavelengths is of little consequence.

• Sunlight being predominantly yellow-green may have something to do
  with flowers & fruits having attractive blue/violet & yellow/red colors:

[b][color=#0000FF]Superposition of spectra of chlorophyll a and b with oenin, a typical anthocyanin, in an acidic solution. While chlorophylls absorb in the blue and yellow/red parts of the visible spectrum, oenin absorbs mainly in the green part of the spectrum, where chlorophylls do not absorb at all.[/color][/b]

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<<Anthocyanins (from Greek: ἀνθός (anthos) = flower + κυανός (kyanos) = blue) are water-soluble vacuolar pigments that may appear red, purple, or blue depending on the pH. They belong to a parent class of molecules called flavonoids synthesized via the phenylpropanoid pathway; they are odorless and nearly flavorless, contributing to taste as a moderately astringent sensation. Anthocyanins occur in all tissues of higher plants, including leaves, stems, roots, flowers, and fruits.

In flowers, bright-reds and -purples are adaptive for attracting pollinators. In fruits, the colorful skins also attract the attention of animals, which may eat the fruits and disperse the seeds. In photosynthetic tissues (such as leaves and sometimes stems), anthocyanins have been shown to act as a "sunscreen", protecting cells from high-light damage by absorbing blue-green and ultraviolet light, thereby protecting the tissues from photoinhibition, or high-light stress. This has been shown to occur in red juvenile leaves, autumn leaves, and broad-leaf evergreen leaves that turn red during the winter. The red coloration of leaves has been proposed to possibly camouflage leaves from herbivores blind to red wavelengths, or signal unpalatability, since anthocyanin synthesis often coincides with synthesis of unpalatable phenolic compounds

In addition to their role as light-attenuators, anthocyanins also act as powerful antioxidants. However, it is not clear whether anthocyanins can significantly contribute to scavenging of free radicals produced through metabolic processes in leaves, since they are located in the vacuole and, thus, spatially separated from metabolic reactive oxygen species. Some studies have shown hydrogen peroxide produced in other organelles can be neutralized by vacuolar anthocyanin.
Light absorbance

The absorbance pattern responsible for the red color of anthocyanins may be complementary to that of green chlorophyll in photosynthetically active tissues such as young Quercus coccifera leaves. It may protect the leaves from attacks by plant eaters that may be attracted by green color.>>

[smitty]

Perfect!

[Chris Peterson]

Why are the missing patches all blurry? I thought the absorption occurs only at very certain wave-lengths and not at wave-length +/- couple nanometers.

While atomic absorption and emission spectra are associated with specific electron transitions which result in extremely narrow lines, in the real world we're usually looking at thermal sources, and the atoms involved have a lot of motion. So the lines are broadened by the Doppler effect- the actual emission or absorption observed depends on the velocity of the atom towards or away from us. This blurs the lines.

[Ron-Astro Pharmacist]

Of course I would like the missing spectral lines to be something like dark photons but that is just from someone who has no business contemplating physics at that level.

For me it probably comes from too much exposure to black light as a teenager or some other unreasonable explanation. Other quandaries have shown up over the years as outlined in SA's article entitled "All the Light that Ever Was." Oblers' paradox provides a more validated history regarding the mystery of light. Ron's paradox is that he just insn't bright enough. But he keeps trying.

[rj rl]

Great point, Chris! Didn't think of that at all.

[Dad is watching]

Why are the missing patches all blurry? I thought the absorption occurs only at very certain wave-lengths and not at wave-length +/- couple nanometers.

While atomic absorption and emission spectra are associated with specific electron transitions which result in extremely narrow lines, in the real world we're usually looking at thermal sources, and the atoms involved have a lot of motion. So the lines are broadened by the Doppler effect- the actual emission or absorption observed depends on the velocity of the atom towards or away from us. This blurs the lines.

Does this mean that the makeup various layer of the suns atmosphere (photosphere) can be determined by the blurring of the absorption lines? Wherein the more volatile and active layers (blurred absorption lines) can show which elements are located at which various 'altitudes' of regions?

[Chris Peterson]

While atomic absorption and emission spectra are associated with specific electron transitions which result in extremely narrow lines, in the real world we're usually looking at thermal sources, and the atoms involved have a lot of motion. So the lines are broadened by the Doppler effect- the actual emission or absorption observed depends on the velocity of the atom towards or away from us. This blurs the lines.

Does this mean that the makeup various layer of the suns atmosphere (photosphere) can be determined by the blurring of the absorption lines? Wherein the more volatile and active layers (blurred absorption lines) can show which elements are located at which various 'altitudes' of regions?

Not really. The surface of the Sun is essentially opaque. We don't see down inside. And the thermal continuum washes out emission lines. So all we have are the absorption lines from layers above the photosphere. We learn something about the thermal characteristics of that tenuous atmosphere, but not much else.

[aileen]

I really like the chlorophyll idea. Maybe in the past plants had all different colors, but only the green/yellow ones were supported by most energy and were selected by evolution. But this is just a bold guess.

Here is my two cents: maybe the spectrum is also dependent on where the sunlight is collected and measured. If the experiment was run on the earth, then the sunlight had already travelled a very long distance and some frequencies might have been attenuated (sunlight was filtered by the substances in space). And that's why we are not seeing all the colors. But if we collect sunlight on the sun, then spectrum might be more complete.

[Slawomir]

I am wondering whether sunlight being predominantly yellow-green has something to do with chlorophyll having green colour as well.

It doesn’t. It is not to a plant’s advantage to reflect away the predominant wavelengths of its energy source, so the colors are probably just a coincidence. Most plants have such a low albedo anyway, that the fact that they reflect slightly more green than other wavelengths is of little consequence.

Thank you for your reply Ricky. However, it is quite difficult for me to accept that chlorophyll's green colour is just a coincidence and not a result of evolutionary processes that give plants a better chance of survival. Maybe reflecting predominant wavelengths has something to do with efficiency of photosynthesis? I like to think that the Universe is "Newtonian" and that nothing is without a consequence.

[Chris Peterson]

I really like the chlorophyll idea. Maybe in the past plants had all different colors, but only the green/yellow ones were supported by most energy and were selected by evolution. But this is just a bold guess.

Certainly, you need to consider evolutionary processes. But such processes rarely yield ideal solutions. Photosynthesis is a complex process and probably only evolved once. And the process using chlorophyll primarily uses red light. Different plant colors have evolved, in part to help make more efficient use of other parts of the spectrum. But the underlying process for all is not optimized for the color of the Sun.

Here is my two cents: maybe the spectrum is also dependent on where the sunlight is collected and measured. If the experiment was run on the earth, then the sunlight had already travelled a very long distance and some frequencies might have been attenuated (sunlight was filtered by the substances in space). And that's why we are not seeing all the colors. But if we collect sunlight on the sun, then spectrum might be more complete.

The spectral structure of light is unaffected by distance traveled (except for cosmological distances, where the expansion of space itself creates redshift). There's no difference in the color of the Sun above its photosphere and the color of the Sun at the top of our atmosphere. There are slight shifts introduced by our atmosphere, but they are pretty minor.

[neufer]

I really like the chlorophyll idea. Maybe in the past plants had all different colors, but only the green/yellow ones were supported by most energy and were selected by evolution. But this is just a bold guess.

Certainly, you need to consider evolutionary processes. But such processes rarely yield ideal solutions. Photosynthesis is a complex process and probably only evolved once. And the process using chlorophyll primarily uses red light. Different plant colors have evolved, in part to help make more efficient use of other parts of the spectrum. But the underlying process for all is not optimized for the color of the Sun.

http://www.livescience.com/1398-early-e ... gests.html

[Chris Peterson]

Certainly, you need to consider evolutionary processes. But such processes rarely yield ideal solutions. Photosynthesis is a complex process and probably only evolved once. And the process using chlorophyll primarily uses red light. Different plant colors have evolved, in part to help make more efficient use of other parts of the spectrum. But the underlying process for all is not optimized for the color of the Sun.

http://www.livescience.com/1398-early-e ... gests.html

Yes, it's certainly likely that there were other photosynthetic chemistries. But what I meant is that the chlorophyll system appears to have only developed once (quite early), and it is very limited in terms of its ability to change under evolutionary pressure.

[Animal of Stone]

Apparently the sun supports marriage equality! (With a few colors unrecognized...)

You bet. Apparently the sun supports all life on this planet. And congratulations to the Americans and APODs timing is perfect !!

[geckzilla]

Apparently the sun supports marriage equality! (With a few colors unrecognized...)

You bet. Apparently the sun supports all life on this planet. And congratulations to the Americans and APODs timing is perfect !!

There are some exceptions to this living around deep ocean hydrothermal vents. Edit: hydrothermal? Geothermal? Volcanic thingies...

[Chris Peterson]

You bet. Apparently the sun supports all life on this planet. And congratulations to the Americans and APODs timing is perfect !!

There are some exceptions to this living around deep ocean hydrothermal vents. Edit: hydrothermal? Geothermal? Volcanic thingies...

Maybe. But only in the sense of direct dependence for energy. In other respects, even life around hydrothermal vents is probably still dependent on the Sun, and it is more likely than not that life itself developed in an environment dependent on the Sun, and then migrated to and evolved in spots where the Sun plays little or no role in the biotic energy cycles.

[mollwollfumble]

This image has been on APOD before, even the text is copied either verbatim or almost verbatim from the earlier APOD. The link is to the same 1995 article where some lines in the Sun's spectrum have still not been reliably identified, some may be higher ionisations of Fe, but other remain a complete mystery. What this APOD totally misses is a brand new scientific paper from June 2015 that says that we can't even make sense of the spectral lines of Oxygen in the Sun's atmosphere. We haven't a clue how much oxygen is in the Sun. Spectral line evidence is grossly inconsistent, and even more inconsistent unless we have the Sun’s nickel content wrong, and helio-seismicity doesn’t clarify the issue. http://arxiv.org/pdf/1506.00931.pdf "The photospheric solar oxygen project".