Explanation: What color is the universe? More precisely, if the entire sky were smeared out, what color would the final mix be? This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies. The answer, depicted above, is a conditionally perceived shade of beige. In computer parlance: #FFF8E7. To determine this, astronomers computationally averaged the light emitted by one of the larger samples of galaxies analyzed: the 200,000 galaxies of the 2dF survey. The resulting cosmic spectrum has some emission in all parts of the electromagnetic spectrum, but a single perceived composite color. This color has become much less blue over the past 10 billion years, indicating that redder stars are becoming more prevalent. In a contest to better name the color, notable entries included skyvory, univeige, and the winner: cosmic latte.
What is the context of the question? Is it asking the color from the surface of Earth? If so then day or night? If not the surface of Earth then where? If daytime on the surface of Earth then why is it not Blue? If nighttime on the surface of Earth then why is it not nearly Black? I think the question needs clarification. And saying it is the colors excluding Black space contradicts the entire sky were smeared out.
Confused wrote: ↑Sun Dec 27, 2020 7:06 am
What is the context of the question? Is it asking the color from the surface of Earth? If so then day or night? If not the surface of Earth then where? If daytime on the surface of Earth then why is it not Blue? If nighttime on the surface of Earth then why is it not nearly Black? I think the question needs clarification. And saying it is the colors excluding Black space contradicts the entire sky were smeared out.
Almost all of the light of the Universe comes from stars or from active black holes like quasars. Supernovas most certainly produce light, too, but they are very transient objects, and they are produced by stars anyway.
So the "latte color" of the Universe is the combined light of all stars, all quasars and all other light sources in the entire Universe. The combined color is latte.
The reason why the color of the Universe is latte is because the Universe is well past its most "ferocious" age of star formation. So let's try to understand stars, star formation adn star death.
The star formation of the Universe peaked some 11 billion years ago. Ever since then, the amount of star formation has kept dropping, so that by now it has dropped by 97%.
Every burst of star formation creates a relatively small number of massive blue stars, and a much larger number of small non-blue, often yellow and reddish, stars.
The massive blue stars are extremely bright. A star that is a hundred times as massive as the Sun can shine a million times as bright. Conversely, a star that contains a tenth of Sun's mass my produce one part in a thousand of the Sun's energy.
But the massive blue stars quickly burn out and die in brilliant supernovas. Stars like the Sun last 10 billion years. Only a small number of all the solar mass stars that were ever born in the Universe have reached the end of their life cycles and died as white dwarfs.
And not a single star like tiny red dwarf Proxima Centauri that was ever born in the Universe has ever died, unless it fell into a black hole or was eaten by a neutron star.
So the number of small red stars in the Universe keeps growing, while the number of bright blue stars keeps shrinking.
So every new burst of star formation creates new tiny red stars that won't die for maybe a trillion years. Many, but not all, bursts of star formation also create some brilliant blue stars which shine mightily, but soon die.
What are you left with?
A latte-colored Universe. More milk, please.
Ann
Last edited by Ann on Sun Dec 27, 2020 12:48 pm, edited 1 time in total.
So did they control for redshift? Or, perhaps, a more interesting question: does one even need to control for redshift if it's just as much a property of the universe as the color itself?
rj rl wrote: ↑Sun Dec 27, 2020 10:06 am
So did they control for redshift? Or, perhaps, a more interesting question: does one even need to control for redshift if it's just as much a property of the universe as the color itself?
I think that the color of the Universe has been "de-reddened" when astronomers worked to figure out the overall color of the Universe.
What would the alternative be? All distant objects of the Universe get reddened by the expansion and "stretching" of the Universe. But how do you calculate the "total redshift of the Universe as affecting the overall color of it"? I don't think you can do that. That's why I think that the overall color of the Universe refers to the overall color of all light sources in the Universe at the time and place where their light that now reaches us was originally emitted.
Consider GN-z11, the most distant galaxy discovered by humanity. Its light has reached us as infrared light in a heavily redshifted state.
Originally, however, GN-z11 would have been dominated by ultraviolet light. I think that the astronomers who calculated the color of the Universe would have counted galaxies like GN-z11 as predominantly ultraviolet sources, not as all infrared ones.
cosmiclatte_jhu_960.jpg (7.35 KiB) Viewed 10853 times
Just my own opinion but, I kindly disagree! That may be the average color of a galaxy! The universe contains all the (no light) between galaxies; which would make it a lot darker! I don't really care though!
"It is interesting to compute the perceived color of the cosmic spectrum to the human eye, using standard color matching functions CIE (1971,
1986). Integrating these through the cosmic spectrum we have computed RGB values of 0.269, 0.388, 0.342. This corresponds to a blue-green
color, the closest match in standard RGB color lists, with the same color balance (normalisation or brightness is of course arbitrary), is ‘pale
turquoise’. This is not a blackbody color, but this makes sense as the cosmic spectrum is a composite of young blue populations and old red
populations. It is robust against choice of redshift bins. See http://www.pha.jhu.edu/~kgb/cosspec for a rendering."
Explanation: What color is the universe? More precisely, if the entire sky were smeared out, what color would the final mix be? This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies. The answer, depicted above, is a conditionally perceived shade of beige. In computer parlance: #FFF8E7. To determine this, astronomers computationally averaged the light emitted by one of the larger samples of galaxies analyzed: the 200,000 galaxies of the 2dF survey. The resulting cosmic spectrum has some emission in all parts of the electromagnetic spectrum, but a single perceived composite color. This color has become much less blue over the past 10 billion years, indicating that redder stars are becoming more prevalent. In a contest to better name the color, notable entries included skyvory, univeige, and the winner: cosmic latte.
After spending a few extra annoyed seconds waiting for my slow computer to load the image, I scrolled down and realized it was actually done!
Since I'm neither a coffee nor a milk drinker, I take offense with the term "cosmic latte". Seems like astronomers trying to be too cute once again to appeal to the public. Cosmic Beige is clearly the correct term.
I also have yet to know what "2dF" stands for even after following half a dozen links. Yeah, it's the first part of 2dFGRS, where GRF stands for Galaxy Redshift Survey, but nowhere is "2dF" explained. <sigh>
And I echo others' posts bemoaning the ambiguity of the meaning of "average color of the universe". But this APOD certainly has given us much to think about and discuss on a lazy Sunday morning!
EDIT: one more thing: I find it very reassuring that this "cosmic beige" is probably my ideal background color for books both real and digital. Very easy on the eyes.
EDIT 2: and yet another thing: I think I disagree with Ann about redshift. It seems to me that it makes more sense to take the redshift into account (that is, to use the redshifted light, not how it was when it was emitted) when averaging the color of all light hitting an observer from all the galaxies in the universe. That way, the resulting average would be the same for all observers everywhere in the universe, dependent only on the time since the universe banged. Also, this average only makes sense if done in space outside of the influence of a planetary atmosphere, again, to make it the same for all observers anywhere in the universe.
EDit 3: <sigh> No sooner had I posted this when I realized that where one is in the universe DOES matter. For example, for someone near the core of a galaxy, their light would be dominated by the local star population, as opposed to someone in the outskirts of a galaxy or between galaxies. So, the average color can't be just time-dependent. Too bad.
-- "To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
johnnydeep wrote: ↑Sun Dec 27, 2020 3:47 pm
I also have yet to know what "2dF" stands for even after following half a dozen links. Yeah, it's the first part of 2dFGRS, where GRF stands for Galaxy Redshift Survey, but nowhere is "2dF" explained. <sigh>
Confused wrote: ↑Sun Dec 27, 2020 7:06 am
What is the context of the question? Is it asking the color from the surface of Earth? If so then day or night? If not the surface of Earth then where? If daytime on the surface of Earth then why is it not Blue? If nighttime on the surface of Earth then why is it not nearly Black? I think the question needs clarification. And saying it is the colors excluding Black space contradicts the entire sky were smeared out.
Almost all of the light of the Universe comes from stars or from active black holes like quasars. Supernovas most certainly produce light, too, but they are very transient objects, and they are produced by stars anyway.
So the "latte color" of the Universe is the combined light of all stars, all quasars and all other light sources in the entire Universe. The combined color is latte.
The reason why the color of the Universe is latte is because the Universe is well past its most "ferocious" age of star formation. So let's try to understand stars, star formation adn star death.
The star formation of the Universe peaked some 11 billion years ago. Ever since then, the amount of star formation has kept dropping, so that by now it has dropped by 97%.
Every burst of star formation creates a relatively small number of massive blue stars, and a much larger number of small non-blue, often yellow and reddish, stars.
The massive blue stars are extremely bright. A star that is a hundred times as massive as the Sun can shine a million times as bright. Conversely, a star that contains a tenth of Sun's mass my produce one part in a thousand of the Sun's energy.
But the massive blue stars quickly burn out and die in brilliant supernovas. Stars like the Sun last 10 billion years. Only a small number of all the solar mass stars that were ever born in the Universe have reached the end of their life cycles and died as white dwarfs.
And not a single star like tiny red dwarf Proxima Centauri that was ever born in the Universe has ever died, unless it fell into a black hole or was eaten by a neutron star.
So the number of small red stars in the Universe keeps growing, while the number of bright blue stars keeps shrinking.
So every new burst of star formation creates new tiny red stars that won't die for maybe a trillion years. Many, but not all, bursts of star formation also create some brilliant blue stars which shine mightily, but soon die.
What are you left with?
A latte-colored Universe. More milk, please.
Ann
A lovely clear and concise explanation! Thank you for both that and the images along with it.
Confused wrote: ↑Sun Dec 27, 2020 7:06 am
What is the context of the question? Is it asking the color from the surface of Earth? If so then day or night? If not the surface of Earth then where? If daytime on the surface of Earth then why is it not Blue? If nighttime on the surface of Earth then why is it not nearly Black? I think the question needs clarification. And saying it is the colors excluding Black space contradicts the entire sky were smeared out.
Yes, it's rather silly. Color is a physiological thing, not a physical thing. This image is not "the color of the Universe". In a limited way, it might represent the hue, but intensity is part of color, and clearly the intensity of this image does not match the average intensity of the Universe. To our eyes, the "average color" of the Universe would be very close to black.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
APOD Robot wrote: ↑Sun Dec 27, 2020 5:06 am Explanation: What color is the universe? More precisely, if the entire sky were smeared out, what color would the final mix be? This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies.
<<Although often used interchangeably, the words "#FFF8" and "destiny" have distinct connotations.
Traditional usage defines #FFF8 as a power or agency that predetermines and orders the course of events. #FFF8 defines events as ordered or "inevitable" and unavoidable. This is a concept based on the belief that there is a fixed natural order to the universe, and in some conceptions, the cosmos. Classical and European mythology feature personified "#FFF8 spinners," known as the Moirai in Greek mythology, the Parcae in Roman mythology, and the Norns in Norse mythology. They determine the events of the world through the mystic spinning of threads that represent individual human #FFF8s. #FFF8 is often conceived as being divinely inspired.
#FFF8 is about the present, where every decision an individual has made has led them to their present scenario. However, Destiny is the future scenario, which cannot be determined by decisions an individual will make.
Destiny is used with regard to the finality of events as they have worked themselves out; and to that same sense of "destination", projected into the future to become the flow of events as they will work themselves out.
Fatalism refers to the belief that events fixed by #FFF8 are unchangeable by any type of human agency. In other words, humans cannot alter their own #FFF8s or the #FFF8s of others.
In ancient Greece, many legends and tales teach the futility of trying to outmaneuver an inexorable #FFF8 that has been correctly predicted. This portrayal of #FFF8 is present in works such as Oedipus Rex (427 BCE), the Iliad, the Odyssey (800 BCE), and Theogony. Many ancient Chinese works have also portrayed the concept of #FFF8, most notably the Liezi, Mengzi, and the Zhuangzi. Similarly, and in Italy, the Spanish Duque de Rivas' play that Verdi transformed into La Forza del Destino ("The Force of Destiny") includes notions of #FFF8. In England, #FFF8 has played a notable literary role in Shakespeare's Macbeth (1606), Thomas Hardy's Tess of the d'Urbervilles (1891), Samuel Beckett's Endgame (1957), and W.W Jacobs' popular short story "The Monkey's Paw" (1902). In America, Thornton Wilder's book The Bridge of San Luis Rey (1927) portrays the conception of #FFF8. In Germany, #FFF8 is a recurring theme in the literature of Hermann Hesse (1877–1962), including Siddharta (1922) and his magnum opus, Das Glasperlenspiel, also published as The Glass Bead Game (1943). And by Hollywood through such characters as Neo in The Matrix. The common theme of these works involves a protagonist who cannot escape their destiny, however hard they try. In Neil Gaiman's graphic novel series The Sandman, destiny is one of the Endless, depicted as a blind man carrying a book that contains all the past and all the future. "Destiny is the oldest of the Endless; in the Beginning was the Word, and it was traced by hand on the first page of his book, before ever it was spoken aloud.">>
Last edited by neufer on Mon Dec 28, 2020 2:07 pm, edited 1 time in total.
johnnydeep wrote: ↑Sun Dec 27, 2020 3:47 pm
I also have yet to know what "2dF" stands for even after following half a dozen links. Yeah, it's the first part of 2dFGRS, where GRF stands for Galaxy Redshift Survey, but nowhere is "2dF" explained. <sigh>
So it was bluer in the past. Is there a version of this with time along the X-axis to show how the colour has changed over the life of the Universe so far and, if possible, project it into the future?
rj rl wrote: ↑Sun Dec 27, 2020 10:06 am
So did they control for redshift? Or, perhaps, a more interesting question: does one even need to control for redshift if it's just as much a property of the universe as the color itself?
My apologies to you! Yes, redshift is indeed incredibly important when calculating the color of the Universe. Ivan K. Baldry et al. discuss it at length in this arXiv-paper from August 15, 2018. Unfortunately, the text is so math-heavy that I can't make sense of it at all!
"It is interesting to compute the perceived color of the cosmic spectrum to the human eye, using standard color matching functions CIE (1971,
1986). Integrating these through the cosmic spectrum we have computed RGB values of 0.269, 0.388, 0.342. This corresponds to a blue-green
color, the closest match in standard RGB color lists, with the same color balance (normalisation or brightness is of course arbitrary), is ‘pale
turquoise’. This is not a blackbody color, but this makes sense as the cosmic spectrum is a composite of young blue populations and old red
populations. It is robust against choice of redshift bins. See http://www.pha.jhu.edu/~kgb/cosspec for a rendering."
New Scientist wrote a little about it back in 2002 and posted two pictures, one of the original but now discarded Universal Turquoise, the other of the subsequently accepted Cosmic Latte:
In January, the true colour of the Universe was declared as somewhere between pale turquoise and aquamarine, by Ivan Baldry and Karl Glazebrook at Johns Hopkins University in Baltimore Maryland.
They determined the cosmic colour by combining light from over 200,000 galaxies within two billion light years of Earth. The data came from the Australian 2dF Galaxy Redshift Survey at the Anglo-Australian Observatory in New South Wales, Australia.
Glazebrook now says the true colour this data gives is closer to beige. “I’m very embarrassed,” he says, “I don’t like being wrong.”
The mistake was caused by a bug in the software Glazebrook had used to convert the cosmic spectrum into the colour the human eye would see if it was exposed to it. “There’s no error in the science, the error was in the perception,” says Glazebrook.
Wrong shade of white
Glazebrook has now teamed up with Mark Fairchild of the Munsell Color Science Laboratory at the University of Rochester in New York, who pointed out his mistake last month.
Fairchild realized the software Glazebrook was using actually took a slightly pinky looking colour as white. “There was a huge green shift due to the erroneous white point,” he says.
When this was corrected, the colour was actually on the pinky side of white, a slight beige colour...
DL MARTIN wrote: ↑Sun Dec 27, 2020 6:36 pm
I was told time doesn't matter. That there was no 'ago' just 'away'. Funny how when something suits the debate it becomes relevant.
Nobody told you that time doesn't matter.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
One important reason why the Universe is getting redder is that star formation is winding down. Why has that happened?
We may compare the early Universe with the Orion Nebula: small, compact, chock full of gas and in the process of forming new stars. We may compare our present-day Universe with the Lambda Orionis Nebula: large, bloated, distended and mostly "spent".
Consider, too, that most stars in the Universe may be red dwarfs. What is such a multitude of small ruddy dwarfs doing to the Universe's ability to make new stars?
Red dwarf stars make up the largest population of stars in the galaxy, but they hide in the shadows, too dim to be seen with the naked eye from Earth. Their limited radiance helps to extend their lifetimes, which are far greater than that of the sun.
Scientists think that 20 out of the 30 stars near Earth are red dwarfs...
Red dwarfs include the smallest of the stars, weighing between 7.5% and 50% the mass of the sun....
Their low temperature also means that they burn through their supply of hydrogen less rapidly. While other, more massive stars burn through only the hydrogen at their core before coming to the end of their lifetimes, red dwarfs consume all of their hydrogen, inside and outside their core. This stretches out the lifetime of red dwarfs to trillions of years; far beyond the 10-billion-year lifetime of sun-like stars.
What if two thirds of all stars in the nearby Universe are red dwarfs? And what if the average mass of red dwarfs is 30% solar? If that is the case, then a very large fraction of all the gas that has ever been converted into stars in the Universe is found inside red dwarfs.
And these little red stars will live for trillions of years, and during all that time, they will hoard almost all the mass that went into making them in the first place, and they will give almost nothing back to the Universe to make new stars of.
Compare the gas-hoarding characteristics of red dwarfs with the properties of the most massive stars, the O-type stars. They will all explode as supernovas in just a few million years, and even before that, their strong stellar winds will blow much of their original mass out into their surroundings.
These massive stars may give back perhaps four fifths or more of all the mass that originally went into making them. The gas they give back to the Universe will be prime material for new star formation. But massive stars are rare and getting rarer, and red dwarfs are common indeed and getting even more common.
Two major factors are causing star formation to wind down in the Universe:
1) The Universe itself has gone from being small and compact to large and distended.
2) Most of the stars that the Universe has ever formed are small red dwarfs. And these stars hoard their gas for trillions of years and give nothing back for new star formation.
Much of the gas that was once available for star formation in the Universe has been locked up inside trillions and quadrillions of small red dwarfs.
Ah, but for the most part, the universe is nearly transparent.
My suggestion of a nomme for that color is: "univeclear". ("uniclear" is shorter, but seems too close to the word "unclear".)
... This color will not render well on any page or computer screen. Instead, look at a color you like from a distance of 6 feet and just imagine how the color has changed as it has travelled to your eyes.
I like this APOD, because it got us all thinking and discussing. The main thing it taught me is that there are probably lots of different versions of this question, each with its own answer (well, perhaps some of the versions of the question don't even have an answer). And a number of them are rather fun to think about.
Cosmic Latte: The Average Color of the Universe
Ever since then, 
Stars like the Sun last 10 billion years.
Only a small number of all the solar mass stars that were ever born in the Universe have reached the end of their life cycles and died as white dwarfs.
More milk, please.
I don't really care though!
