What color is the sun?

[Admin]

The color of the sun reveals a range of information about our star including the stages of its life and the nature of light and how it interacts with the atmosphere of Earth.

What color is the sun? : Read more

 

[Unclear Engineer]

Umm . . . Why does this article follow the Headine

"What color is the sun? Spoiler alert: It's not yellow."

with the statement

"The sun is officially classified as a yellow dwarf star or a G2 V star."

[Emphases mine]

 

[Helio]

“The sun emits light across all the visible colors in the electromagnetic spectrum fairly evenly.”

Since most distributions of solar spectral emissions use an energy distribution, then it's not at all even. Just glance at these common graphs here.

But, if we use a photon flux distribution model, the distribution is very flat. [Here's one I did years ago to compare the two plot methods.]

When these come together united in sunlight the sun appears white.

I've never heard it expressed quite that way, but I do like it! But it should be made clear that combining the colors is not an answer to a white result. [I've seen many claim the Sun is white because it has all the colors.] The light from"red" and "blue" stars -- these too have all the colors -- can be combined as well. Are they white?

This is useful because if this balance was thrown off colors less favored would be difficult to see.

It's plausible, however, that evolution would easily adjust to "unbalanced" colors. Yet, evolution is passive, so many evolved creatures see things a lot differently. Some see farily well in infrared. Others can see in some UV (white tail deer), and with only two color cones vs. our three. Birds have four color cone types, which would be cool to grasp what they might see.

The sun is officially classified as a yellow dwarf star or a G2 V star.

I've seen technical work suggesting the "yellow" adjective is not any sort of an official element of the Sun's classification. But, I think this might be a ducking action to avoid the fact that it's not yellow.

The first effective star classification system came from Fr. Secchi who did use color as a general guide. But his primary effort in his classification system came from the stellar spectra. Since Secchi considered the Sun to be similar in spectra to Capella (a yellowish white star), then the Sun fell into his "yellow" class. I suspect this began the long erroneuous trek in all of astronomy to assume our Sun is yellow, or some hint of yellow. But, the "Sun Ain't Yeller!" Not even a hint of a tint (as seen from space without atmospheric color distortion).

 

[Unclear Engineer]

We have been through this before, so I am not going to repeat. I was just commenting on the article's obvious self-contradiction.

But, the article does make it look like "yellow" is hotter than "red" and cooler than "blue", which does make it seem reasonable to classify our Sun as a "yellow star" if we consider its temperature in comparison to the range of other stars' temperatures.

As we have discussed before, "yellow" is a matter of perception with high variability among individuals. And, it is subjective even by any particular individual depending on what else it is seen with - our minds shift color perceptions to redefine "white" under varying sources of illumination with differing color spectra, once we have an object that we expect to be white.

So, this argument seems pretty silly to me. The sun's spectrum is rather flat in the frequency range that humans can see, and "yellow" is pretty much right in the middle of that range.

 

[Helio]

I somehow failed to notice that the article extended past the information on the author. Normally I see the author info at the end of the article. I did think three paragraphs was short,.

But, the article does make it look like "yellow" is hotter than "red" and cooler than "blue", which does make it seem reasonable to classify our Sun as a "yellow star" if we consider its temperature in comparison to the range of other stars' temperatures.

Yes, it was suspected early on that star color and temperature correlated, but the absorption lines told the greater story, followed by spectral energy distributions. Color is almost always a side feature.

But color only worked as a guide if white is ignored. White stars originally were in their own class, per Secchi and others, but, somehow, yellow got too attached to many stars, including the Sun.

Given how easy it is to falsify a yellow color, it's quite surprising to me that so little effort was given to it. I have to believe solar physicists quickly realized this as their projections were so white, and, notably, after the blue-end atmospheric extinctions. I'm still curious how this "yellow" perpetuation happened, though I think my guess (stated earlier) might be accurate enough.

As we have discussed before, "yellow" is a matter of perception with high variability among individuals. And, it is subjective even by any particular individual depending on what else it is seen with - our minds shift color perceptions to redefine "white" under varying sources of illumination with differing color spectra, once we have an object that we expect to be white.

Yes. "Color constancy" plays a key role in causing us to see white when a computer model says it is, say, peachy pink *cough*.

It would be interesting to find a bright and, if possible, whiter reference light source near a dim solar projection to see if any color shift occurs. My guess is that the source would have to be too high a temperature causing it to be too blue, perhaps.

Regardless, color should be treated for what it is, not how we can use and abuse it. It's simply what the vast majority would see, so not all that subjective in my opinion. [There are tint puzzles that test one's ability to see small variations in color.] A white star, as seen evenly attenuated in space, should be labeled a white star, especially when the other color hypotheses have been falsified.

So, this argument seems pretty silly to me. The sun's spectrum is rather flat in the frequency range that humans can see, and "yellow" is pretty much right in the middle of that range.

Agreed. Even the HR diagram includes a white star region (far too narrow a region, IMO), so I don't get why "yellow" is so appealing. Correcting from a "yellow dwarf", however, to a "white dwarf" means that the dwarf designation should also be tweaked. Perhaps it's just "too much squeeze for the juice" to toss this up at the IAU meetings.

 

[billslugg]

The whitest diamonds are "Exceptional white plus". They are judged against a background of magnesium oxide, illuminated by light from the northern sky*, with the Sun more than ten degrees above the horizon in the south in a room with white walls.(1)

To me, this is the best definition of "white" that there is, magnesium oxide illuminated by the northern sky. Thus, the Sun is white.

*Direct sunlight cannot be used to judge diamond color because the UV component flouresces the diamond in the blue range, cancelling out some of the yellow.

1 - "Diamonds" Eric Bruton, 2nd Ed, 1978, p264

 

[Helio]

The whitest diamonds are "Exceptional white plus". They are judged against a background of magnesium oxide, illuminated by light from the northern sky*, with the Sun more than ten degrees above the horizon in the south in a room with white walls.(1)

That is a min. of 5.7 air masses, so a slight yellow tint is likely. So if a compound absorbs a little of the reds it should appear quite white. If whiter than the source light then it could be the eye’s reference white. A sp. irr. of it would be interesting.

To me, this is the best definition of "white" that there is, magnesium oxide illuminated by the northern sky. Thus, the Sun is white.

*Direct sunlight cannot be used to judge diamond color because the UV component flouresces the diamond in the blue range, cancelling out some of the yellow.

Ideally, a host of known white sources, with known SEDs, shown to a large group in a black room would best define white,I suspect. “White” should be treated as a color, which is story told only by eyes.

Given how flat a photon flux distribution is for the Sun, it would be easy, perhaps, to just use a flat one for a “white” def.

 

[Helio]

Here’s a question I can never seem to avoid asking myself when reading these color articles…

How many incorrect color choices are illustrated for the Sun vs. correct ones?

 

[Pogo]

Probably most of them. Almost all artwork that I see depicts the Sun very yellow, which it certainly is not.
Also, it is the perception of the human eye given its evolutionary history. An intelligent being from another world let’s say orbiting something like Betelgeuse, given an eye history which is likely quite different, would likely define white differently.

 

[Helio]

Imagine an article about, say, tree color, and 16 different colors of trees were illustrated…none green. This is the case here, but it’s typical of almost every such article on the Sun.

Planets are usually shown in their natural color, hosted by a false color image of the big bright thing they circle.

 

[Unclear Engineer]

I just don't see why this bothers some of you so much. Yes, we see an even distribution of all the colors that our eyes can detect as "white", and those colors are the ones that our Sun produces the most of. Not surprising, because evolution formed us to take maximum advantage of the light from our particular star. Living, seeing beings on planets circling different stars would probably have different definitions of "white".

But, if you include the entire electromagnetic frequency spectrum, from radio waves through visible light into extreme cosmic gamma rays, then oud Sun is not emitting the all in an even distribution. What is roughly the center frequency of its rather broad distribution peak in the range we can see? Yellow is the answer.

So, I have no problem with astronomers categorizing our Sun as a "yellow" star for comparison to hotter "blue" stars and cooler "red" stars.

Nor do I have any problem with artists depicting the difference between the shadow and sunlit areas as bluer and yellower, because our brains are what are making that distinction and the artists are simply using pigments to make our brains "see" the same color contrasts under "indoor" (maybe artificial) light that we would see for the real scene under natural light.

As an aside, I have been converting some old florescent light fixtures to LED bulbs. The old florescent light bulbs produce light with a decidedly greenish tint. But the new LED bulbs come in 4 choices of "color temperatures": 3900K, 4500K, 5500K and 6500K. Of course, those are not full spectrum color distributions for the black body emissions at those temperatures, because they are really the result of different phosphor materials with limited spectrums. Anyway, we tried each LED type, noting the differences. Then tried one of each at the same time in the 4 receptacles of one fixture. That one-of-each color spectrum was far more like natural light than when 4 of any of the individual "temperature" bulbs were used. But, none of them looked "yellow" or "blue" or "green" when viewed individually, because or brains adjusted the color perception to make our white appliances look white under all conditions. Even so, when taking pictures of scale model scenes that are made to look like the real thing, we know that doing so under any form of artificial light is no where near as convincing as doing it under actual sunlight, outside, where the blue light from the sky and the direct light from the sun naturally illuminate different parts of the models just as the would the real, full scale things being modeled.

 

[Helio]

But, if you include the entire electromagnetic frequency spectrum, from radio waves through visible light into extreme cosmic gamma rays, then oud Sun is not emitting the all in an even distribution. What is roughly the center frequency of its rather broad distribution peak in the range we can see? Yellow is the answer.

So what color are the yellow stars , which are cooler than your “yellow” that appear white?

Science is self-correcting, but this issue is interesting partly because it is somewhat trivial. Nevertheless, any grade school kid knows that white objects aren’t yellow. Either the Sun is yellow or it’s not.

“White” is not required to be in the spectrum to best define white stars. Cooler yellow stars are yellow for a reason. The Sun is not among them.

Nor do I have any problem with artists depicting the difference between the shadow and sunlit areas as bluer and yellower, because our brains are what are making that distinction and the artists are simply using pigments to make our brains "see" the same color contrasts under "indoor" (maybe artificial) light that we would see for the real scene under natural light.

I have no complaint for an artistic touch for the Sun, but to almost never see it in its natural color is just strange, especially when the topic is the Sun’s color.

As an aside, I have been converting some old florescent light fixtures to LED bulbs. The old florescent light bulbs produce light with a decidedly greenish tint. But the new LED bulbs come in 4 choices of "color temperatures": 3900K, 4500K, 5500K and 6500K. Of course, those are not full spectrum color distributions for the black body emissions at those temperatures, because they are really the result of different phosphor materials with limited spectrums. Anyway, we tried each LED type, noting the differences. Then tried one of each at the same time in the 4 receptacles of one fixture. That one-of-each color spectrum was far more like natural light than when 4 of any of the individual "temperature" bulbs were used. But, none of them looked "yellow" or "blue" or "green" when viewed individually, because or brains adjusted the color perception to make our white appliances look white under all conditions. Even so, when taking pictures of scale model scenes that are made to look like the real thing, we know that doing so under any form of artificial light is no where near as convincing as doing it under actual sunlight, outside, where the blue light from the sky and the direct light from the sun naturally illuminate different parts of the models just as the would the real, full scale things being modeled.

I’d enjoy seeing your models under any light.

 

[Unclear Engineer]

I have no complaint for an artistic touch for the Sun, but to almost never see it in its natural color is just strange, especially when the topic is the Sun’s color.

Well, if you stop and think about how a picture of a white sun would look on a sheet of white paper or a white background computer screen, you would realize that it would need an outline of some sort to even be noticeable. (And then we could argue that the sun's "atmosphere" and even its "spots" are not really black.)

 

[Helio]

Well, if you stop and think about how a picture of a white sun would look on a sheet of white paper or a white background computer screen, you would realize that it would need an outline of some sort to even be noticeable.

Right. Tha Crayola choices likely has contributed to the color conundrum. I’m not criticizing the use of color, but the lack of demonstration of its natural color. The imbalance is surprising.

Many authors in recent years state the Sun is white, unlike a decade or more ago. So there is a slow, improving trend.

 

[Helio]

One thing I can count on every time we jump into the color conundrum is that an article will soon surface for yet more clear evidence of color used to garner attention rather than represent, say,….color.

It’s like sitting at a tee box awaiting some big name to set-up the ball as if coaxing a pest like me to launch it down the fairway. But it’s more like a driving range with hundreds of balls awaiting pickup.

Here’s a fun ball…https://skyandtelescope.org/sky-and-telescope-magazine/inside-the-december-2022-issue/

It’s a wonderful story behind finding and understanding the first “ white dwarf”. But the yellow artwork on the cover is to represent Eridani B, surface temperature…17,500K, Type A2.

On iPhone awaiting flight.

 

[Pogo]

I also think that closeup images of the Sun showing spots and other details, the general color is more from the filters and recording equipment than the surface color itself.

 

[Helio]

I also think that closeup images of the Sun showing spots and other details, the general color is more from the filters and recording equipment than the surface color itself.

Right. The color slices in the OP article each represent a set temperature result. I am fairly sure they are very consistent with these temperature —false color correlations to avoid ambiguity.

SDO does include a white (white gray) image representing the more natural solar color of the photosphere.

So this story is far more “about degree, not kind”. The plethora of yellow images and other erroneous colors are way off balance. Calling the Sun white should warrant a bright white image now and then, right?

My avatar is such an image and it does, of course, demonstrate the CLV.