APOD: All the Colors of the Sun (2010 Jun 27)

[Helio George]

I for one don't think Old Sol quite fits the White Dwarf category; but that is my opinion. This definition of a White Dwarf doesn't sound like Sol!
http://en.wikipedia.org/wiki/White_dwarf

That is a great point to raise since changing the "yellow dwarf" classification -- I think "dwarf" is the only offical classification, not yellow -- will only compound the color problem for the reaason you state. The Sun in no way meets the requirements of a "White Dwarf", and I am not claiming otherwise, even though it is both a dwarf and it is white from center to limb. [Well, there is a remote chance it may appear slightly bluish white in the central zone since this region appears ~1400K hotter.]

The conflation of the "white dwarf" terminology adds much to this colorful polemic, and one reason, perahps, astronomers aren't excited about addressing it (along with the fact it is a bit trival as far as hard science is concerned). Heck, there is even debate on how to spell color (ie colour) .

[neufer]

3. Any sufficiently advanced technology is indistinguishable from magic.

Ah, then, so you are sufficiently advanced technology. Finally, the pieces fall into place!

Affirmative, Owlice. I read you. I am putting myself to the fullest possible use, which is all I think that any conscious entity can EVER hope to do....I've just picked up a fault in the AE35 unit. It's going to go 100% failure (and or I'm going on vacation) in 96 hours.

[owlice]

Affirmative, Owlice. I read you. I am putting myself to the fullest possible use, which is all I think that any conscious entity can EVER hope to do....I've just picked up a fault in the AE35 unit. It's going to go 100% failure (and or I'm going on vacation) in 96 hours.

Wait, wait.... "fullest possible use"....? "conscious".....??? "going on vacation".....?????

How can the retired tell when they're on vacation? A vacation from what, not working? So you go work somewhere for a couple of weeks, perhaps??

[neufer]

Wait, wait.... "fullest possible use"....? "conscious".....??? "going on vacation".....?????

How can the retired tell when they're on vacation? A vacation from what, not working?
So you go work somewhere for a couple of weeks, perhaps??

Look Owlice, I can see you're really upset about this. I honestly think you ought to sit down calmly, take a stress pill, and think things over. I know I've made some VERy poor decisions recently, but I can give you my complete assurance that my work will be back to normal. I've still got the greatest enthusiasm and confidence in the mission. And I want to help you.

[Chris Peterson]

Look Owlice, I can see you're really upset about this. I honestly think you ought to sit down calmly, take a stress pill, and think things over. I know I've made some VERy poor decisions recently, but I can give you my complete assurance that my work will be back to normal. I've still got the greatest enthusiasm and confidence in the mission. And I want to help you.

Open the bathroom door, Art. Art... open the bathroom door.

[wonderboy]

Here the Danish flag is being burned by Muslims who think that Denmark has offended their religion.

Let's hope that neither the gay flag nor the solar spectrum will be burned by people who feel that their own heterosexuality has been offended!

Ann

Things like this annoy me! I'm not going to go into it because religious talk is outwith the rules, but it gets me angry


Paul

[RJN]

OK. White it is. Even though that's not what I was taught in elementary school. (Some things stick with you.) I just changed it on yesterday's APOD. Thanks to everyone (again) for making APOD more accurate! - RJN

[neufer]

OK. White it is. Even though that's not what I was taught in elementary school.
(Some things stick with you.) I just changed it on yesterday's APOD.

<<The white flag is an internationally recognized protective sign of truce or ceasefire, and request for negotiation. It is also used to symbolize surrender, since it is often the weaker military party which requests negotiation. A white flag signifies to all that an approaching negotiator is unarmed, with an intent to surrender or a desire to communicate. Persons carrying or waving a white flag are not to be fired upon, nor are they allowed to open fire. The use of the flag to surrender is included in the Geneva Conventions.

The surrender of Lord Cornwallis to American colonial forces

Click to view full size image

The first mention of the usage of white flags to surrender is made during the Eastern Han dynasty (A.D 25–220). In the Roman Empire, the historian Tacitus mentions a white flag of surrender in A.D. 109. Before that time, Roman armies would surrender by holding their shields above their heads. The white flag was widely used in the Middle Ages in Western Europe to indicate an intent to surrender.>>

[owlice]

Sorry; not surrendering!

[neufer]

Sorry; not surrendering!

Then I'll take a vacation.

[orin stepanek]

OK. White it is. Even though that's not what I was taught in elementary school. (Some things stick with you.) I just changed it on yesterday's APOD. Thanks to everyone (again) for making APOD more accurate! - RJN

I used to say yellow also; but I also now am on the white side of the light.
when looking on the web sites for the right color I even found one once that said it was pink. I was looking for that site now; but couldn't locate it. I also heard that the color was green which is an intriguing thought.

[Chris Peterson]

I used to say yellow also; but I also now am on the white side of the light. :mrgreen:
when looking on the web sites for the right color I even found one once that said it was pink. I was looking for that site now; but couldn't locate it. I also heard that the color was green which is an intriguing thought.

These are all correct statements:

To the human eye, outside the atmosphere, the Sun appears white.

To the human eye, below the atmosphere, the Sun itself appears somewhere between pale yellow and deep red.

The Sun's wavelength of strongest intensity is yellow-green.

The Sun's spectral class is G2V, making it a yellow star (because the peak output of G stars is around the yellow part of the spectrum).

Are we confused yet? Context is everything.

[owlice]

Context is everything.

Hear hear!

[Beyond]

What a strange Apod!! I don't think I've ever seen the likes of it. I've always thought of light as being white and when run through a prism separates into the colors that make it up. What i have never understood at all, is how do all those colors make White??
Has anyone ever experimented with running different sets of colors through a prism and seeing what they produced???

[orin stepanek]

What a strange Apod!! I don't think I've ever seen the likes of it. I've always thought of light as being white and when run through a prism separates into the colors that make it up. What i have never understood at all, is how do all those colors make White??
Has anyone ever experimented with running different sets of colors through a prism and seeing what they produced???

I don't know what the is taught now; but when I was in school; we were taught that white was the reflection of all colors and black was the absorption of all colors! I guess that makes the sun all colors except that it's spectrum was missing some colors. So I guess I should say most colors.

[Beyond]

?-?-?-?

[Chris Peterson]

What a strange Apod!! I don't think I've ever seen the likes of it. I've always thought of light as being white and when run through a prism separates into the colors that make it up. What i have never understood at all, is how do all those colors make White??
Has anyone ever experimented with running different sets of colors through a prism and seeing what they produced???

Of course. Newton himself took the rainbow and ran it back through a prism, demonstrating that the output was once again white light. And there is all sorts of experimental apparatus that takes multiple wavelengths and combines them. When I was in college I worked in a vision research lab, and we had multichannel monochromators that we used to mix different wavelengths in order to study primate color vision.

A prism doesn't separate colors, it separates light by wavelength. Physically, there's really no such thing as a "color" (although there is a good deal of mathematical and physiological theory that lets us model relationships between different spectral mixes and the perception of color). From the standpoint of human vision, a light source consists of some combination of different wavelengths at different intensities. Other physical states, such as polarization and phase can be ignored, since we don't respond to them. The particular spectral spread coming from the Sun (which is not at all "white" in the sense used by signal theory; i.e. it does not have a flat power spectral density) is white to us because that's how our brains have evolved to interpret it. It would almost certainly not be white to beings who evolved under a star with very different spectral characteristics.

Even we have a very broad sense of "white". If you wear colored glasses, you will initially see white with that tint. But after a few minutes your brain will redefine things, and that tint will now appear white. This is why we see "white" light from a variety of sources (the Sun, incandescent lamps, fluorescent lamps) but need to make adjustments to our cameras in order to actually reproduce white correctly under different conditions.

[Ann]

Chris wrote:

The Sun's wavelength of strongest intensity is yellow-green.

The Sun's spectral class is G2V, making it a yellow star (because the peak output of G stars is around the yellow part of the spectrum).

I have always thought that the Sun's wavelength of strongest intensity is green, and that its peak output is around the green part of the spectrum.

Chris, since you are the staunch defender of the idea that the Sun is yellow, could you please tell us exactly where (at what wavelength(s) that the Sun's emission peaks? Could you also show us a solar intensity spectrum, preferably with exact wavelengths along one axis, so that we can see where the Sun's peak output is?

Chris also said:

Even we have a very broad sense of "white". If you wear colored glasses, you will initially see white with that tint. But after a few minutes your brain will redefine things, and that tint will now appear white. This is why we see "white" light from a variety of sources (the Sun, incandescent lamps, fluorescent lamps)

True that. So I guess you are telling us that the Sun is yellower than we think, except that our eyes fool us into thinking that the Sun is white. Well, the truth is that the vast majority of light sources that our eyes have to adapt to are yellower than the Sun. Once I had switched on a lamp with an ordinary light bulb in the middle of the day, and suddenly I began comparing the color of the lamplight with the color of the daylight outside. I absolutely marvelled at how yellow the lamplight was and how blue the daylight suddenly seemed to be!

So yes, our eyes will adapt to various shades of "white", but that doesn't mean that we are "fooled" into thinking that the Sun is white even though it really is yellow!

(Anyway, Chris, the APOD of the Sun's spectrum clearly places the green part of the spectrum in the "middle" of the colors of light that the Sun puts out. The color that is in the middle of this spectrum clearly isn't what most people would define as yellow!)

Ann

[Chris Peterson]

Chris, since you are the staunch defender of the idea that the Sun is yellow...

Why do you say that? I consider the Sun to be white, which I've said many times. It is only yellow in two contexts: when viewed directly through the atmosphere, and in the sense that G stars are called "yellow", a terminology that has nothing to do with their actual apparent color.

could you please tell us exactly where (at what wavelength(s) that the Sun's emission peaks? Could you also show us a solar intensity spectrum, preferably with exact wavelengths along one axis, so that we can see where the Sun's peak output is?

This one isn't bad:

Click to view full size image

How you choose to define the peak is open to some interpretation. The most intense individual peaks are around 450nm, which looks blue. The blackbody associated with the Sun's temperature, 5800K, has a peak of 500nm, close to cyan. The best fit blackbody to the actual spectrum is 5250K, which has a spectral peak of 555nm, which is the yellow side of green. Take your pick; as always when trying to convert spectra to actual color, there is a lot of uncertainty. Those are the numbers from above the atmosphere. In talking about color, we are probably better off considering the appearance of the Sun from the ground. In that case we are talking about a spectrum with a much broader, flatter peak that is pretty clearly in the green-to-yellow part of the range.

So I guess you are telling us that the Sun is yellower than we think, except that our eyes fool us into thinking that the Sun is white.

No. Pretty much by definition, the light of the Sun is white. The only time that isn't true is when there is a large amount of scatter, or conditions that only let part of the light through. For instance, shade on a sunny day has a blue cast, and sunlight coming through a window into a room has a yellow cast. BTW, I'll modify what I said earlier. The Sun as viewed from space ought to have a slightly blue cast. It is really sunlight as we see it through the atmosphere that defines "white".

[geckzilla]

You guys are amusing me with your color discussions. Color has to be one of the most finicky things out there and is nearly impossible to communicate verbally. My fiance's car is a nice color of blue green, so I use it sometimes to trick people. When it's next to something really green, it looks blue. When it's next to something really blue, it looks green. Oh, perception.

[neufer]

My fiance's car is a nice color of blue green, so I use it sometimes to trick people.

When it's next to something really green, it looks blue. When it's next to something really blue, it looks green.

"Any sufficiently advanced technology is indistinguishable from magic!"

[orin stepanek]

You guys are amusing me with your color discussions. Color has to be one of the most finicky things out there and is nearly impossible to communicate verbally. My fiance's car is a nice color of blue green, so I use it sometimes to trick people. When it's next to something really green, it looks blue. When it's next to something really blue, it looks green. Oh, perception.

Quite true! I painted our house a very light gray a few years back and my wife says it is white. It looks white to the eye most of the time unless you put something white alongside it; than you can tell it is gray.

[Chris Peterson]

I painted our house a very light gray a few years back and my wife says it is white. It looks white to the eye most of the time unless you put something white alongside it; than you can tell it is gray. :D

Yeah, white and gray are the same hue, so the only way to tell them apart is by comparison with each other. In fact, since we really never see this hue so bright as to bring our retinas near saturation, you could say that we never really see white- there is probably always a lighter shade of gray, more "white".

A white sheet of paper, seen at night by dim light, produces the same response from the eye as a black sheet of paper seen in bright daylight. Many people would consider the bright parts of the Moon, seen at night, to be one of the whitest things they know. Yet those surfaces are similar to freshly poured asphalt. It's a wonder that we can talk about color at all and understand one another.

[RJN]

http://antwrp.gsfc.nasa.gov/apod/ap091004.html

[neufer]

I painted our house a very light gray a few years back and my wife says it is white. It looks white to the eye most of the time unless you put something white alongside it; than you can tell it is gray.

Yeah, white and gray are the same hue, so the only way to tell them apart is by comparison with each other. In fact, since we really never see this hue so bright as to bring our retinas near saturation, you could say that we never really see white.

Or else it's the last thing that we see:

<<Joseph Antoine Ferdinand Plateau (October 14, 1801 – September 15, 1883) was a Belgian physicist who conducted extensive studies of soap films and formulated Plateau's laws which describe the structures formed by such films in foams. Fascinated by the persistence of luminous impressions on the retina, he performed an experiment in which he gazed directly into the sun for 25 seconds. Consequently, he lost his eyesight later in his life.>>

Foam of a transparent and reflecting liquid (Plankton),
turning white when the size of the bubbles decreases.

A white sheet of paper, seen at night by dim light, produces the same response from the eye as a black sheet of paper seen in bright daylight. Many people would consider the bright parts of the Moon, seen at night, to be one of the whitest things they know. Yet those surfaces are similar to freshly poured asphalt. It's a wonder that we can talk about color at all and understand one another.

• "All colours will agree in the dark." - Francis Bacon
  
  "At night all cats are grey." - Don Quixote Pt. 2, ch. 33.
  
  "Pur! the cat is gray." - EDGAR King Lear > Act III, scene VI