A hex on star colors

By Phil Plait | March 10, 2010 7:22 am

The website called Today I Found Out has an interesting post on Sun factoids, including its color as designated in hex code: #FFF5F2. That code is actually taken from the site vendian.org, put together by Mitchell Charity. He has other star colors listed as well. I found the codes for different stellar types interesting.

starcolorsThe star type is listed, along with the RGB and hex values. The stars go from hottest at the top to coolest at the bottom, and the Sun is roughly a G2V.

The colors are relatively good, in that they are blue at the top and reddish at the bottom. But I was surprised at the lack of color saturation, and that the cooler stars aren’t as red as I would think.

I have spent a lot of time at the eyepiece. Vega, an A0 dwarf star, is distinctly and brilliantly blue, almost a sapphire to the eye. Betelgeuse, an M1 supergiant, is a ruddy orange. I’ve seen a handful of cooler red giants, and to the eye they are very red, not the pastel orangey thing seen here.

Why is this? There are lots of reasons that come to my mind. One is that the way stars shine is inherently different than the way colors are represented on your screen. Stars are hot balls of luminous plasma, glowing like a blackbody. Unless you heat your monitor to that same temperature, you can only approximate the way a star shines, and the colors will be off.

Our eye perceives color oddly, too. Seeing a star against a black sky will give you a different sense of its color than if you see it on your monitor. Even putting a differently colored star in the same field wrecks your color sense. I’ll note that Charity’s star color page has a hex code for the color of planetary nebulae, and that’s a whole nuther can o’ worms.

In my opinion, doing this is an interesting exercise, and a wonderful "teaching moment" on how stars emit light and how we perceive color. But as an exercise in actually trying to mimic star colors, it’s a whole lot tougher than you might think. I’m not saying Charity’s colors are wrong, but I am saying that trying to get hex codes for star colors is like writing down the notes to Beethoven’s Ninth Symphony on paper. It’s a code, and has the right information in it, but it’s not the same as hearing the orchestra.

I’ll also note that the whole point of the first site’s article is that the Sun is white. This is actually an extremely difficult topic to understand — it’s not just scattered blue light that makes the Sun look yellow to us, and I’m still not convinced the Sun does look yellow to us. Charity links to a page about the Sun’s color written by my friend the astronomer Andrew Hamilton, which has some more info on it.

I think the real lesson here is that something we think of as simple — color — is not at all simple! The way colors are emitted by an object, the way our eyes detect color, and most importantly the way our brains interpret that signal, are actually extraordinarily complex processes. I think that’s a very important concept to keep in mind when pondering pretty much any issue: what we take for granted as simple is almost never any such thing.

Tip o’ the artist’s beret to Philippe Hamel.

CATEGORIZED UNDER: Astronomy, Geekery, Piece of mind, Science
MORE ABOUT: color, stellar types, Sun

Comments (53)

  1. Chas, PE SE

    I always enjoyed looking at Beta Cygni (Albireo) because of the lovely contrast. Also: I had thought that the reason Sol was “white” was that we had evolved in its light — if we were a species who had evolved on a planet orbiting a red star, “red” would look “white” to our eye-stalks, and Sol would appear blue in our karah–beh’s (telescopes)…???

  2. Steve

    Great post. To this day, the most mindblowing science lesson I’ve ever had was my 7th grade science teacher showing us that the objects around us don’t have any intrinsic color, that it’s all in our perception.

    I still find myself thinking how amazing colors are now and then. Think of how complex painting actually is in light of all this, pun intended.

  3. Bigfoot

    The single best demonstration I have ever seen on color perception and how relative it all is is the trio of illusions featured here.

    http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html

    Note that this site does not work well with Google Chrome, but it works fine with Internet Explorer.

    If you don’t believe the illusion (if your mind is still trying to trick you), use an opaque piece of paper with a small cutout to mask the surrounding screen when you slide the controls, and you will see the pixels in the focus areas really do not change when the sliders move. Amazing!

  4. Plutonium being from Pluto

    Neat item here. :-)

    For me perhaps the most interesting colour case is Zubeneschamali (Beta Librae) being percieved as green – its spectral & luminosity type is B8 V (blue – or green – dwarf) which looks very blue here but Zubeneschamali historically (and sometimes today) is described as a green star. For instance : the English observer T.W. Webb, who remarked on its “beautiful pale green colour.” (Patrick Moore, ‘The Atlas of the Universe’, Phillips, 1994.)

    However, others are skeptical such as Patrick Moore himself who writes :

    “It [Zubeneschamali] is said to be the only single naked-eye star with a greenish hue, but most people will call it white, and I have never been able to see any colour in it.”

    ( Stars of the Southern Skies, Patrick Moore, 1994.)

    Thus many astronomers such as stellar expert James Kaler take a middle road noting the subjectivity of the issue :

    “Zubeneschamali .. has a long-standing reputation of being not just green but deep green, nineteenth century astronomers flowering over its hue. .. The stars colour seems more to be a matter of personal perception since only some can see it.”

    (Kaler,‘The Hundred Greatest Stars’, Copernicus books, 2002.)

    However, while rare, Zubeneschamali is far from being alone in the “green star” class as other examples exist – although often, as with Antares B, Rasalgethi B and Almach (Gamma Andromedae) these stars are B or early A type companions to red giant and supergiant stars, appearing green mainly due to the effects of contrast. Or is that the full story?

    As Fred Schaaf (2008) notes :

    “The true test of the companion’s colour should be what it looks like when it emerges [during occultations – ed] from behind the dark side of the Moon before Antares [A] bursts back into view. Do observers then see it as green? The answer appears to be a qualified yes. At least some observers see it as distinctly greenish even when Antares itself is still hidden by the Moon. … in 1856, one of the greatest double star observers of all time, W. R. Dawes, watched the companion emerge from behind the Moon and thought it looked greenish.”

    Pages 219-220, Schaaf, ‘The Brightest Stars’, Wiley, 2008.

    Most recently in 2003, Steve Alber, described as a skilled observer by Schaaf also noted Antares B looked greenish when seen alone during another lunar occultation. Interestingly enough, both Antares B and Zubeneschamali share the same spectral class both being B8 blue – or should that be green – dwarfs!

    See : http://stars.astro.illinois.edu/sow/zubenes.html

    I know the BA’s posted ongreen stars – and their absence before here too (related link please?)

  5. Colour is as much physiology and psychology as it is physics. Schrödinger did a lot of work on this before moving to wave mechanics.

    As Feynman noted, there are no green stars!

  6. Off topic: but you guys might have fun with the Cosmologists Caption contest going on here: http://secularcafe.org/showthread.php?p=115939#post115939

    If you’re not a member at SC, I can post something on the thread on your behalf if you have a funny comment.

    Back on topic: the colo(u)r topic is pretty interesting — but aren’t we seeing the entire spectra of visible light produced by each star (as the atmosphere absorbs most UV and shorter wavelengths, and we can’t see wavelengths above red anyway), and the perceived colour is that which our brain registers as dominant? It seems that the perceived colour has to be somewhat subjective.

  7. drow

    “your eyes can deceive you, don’t trust them.”

  8. Jerry

    The hex colours have a white point which is arbitrary, but supposed to be something like the whiteness of, say, a piece of paper. Stars are luminous and much brighter than a piece of paper, so while the hue and saturation may be OK, the luminance is going to be way off.

  9. Plutonium being from Pluto

    Some more points, ideas & theories on Zubeneschamali’s (Beta Librae’s) renowned greenness here :

    * In contrast to many of the “green stars” that are in binary or multiple systems, Zubeneschamali is a single star having no known companions and is located 160 light years away – double the distance of its constellation mate Zubenelgenubi (Alpha Librae) – with four times our Sun’s mass and shining with 300 times our Sun’s luminosity. (Kaler, ’The Hundred Greatest Stars’, Copernicus books, 2002.)

    * Sadly, while B8 dwarf class stars contain notable examples of green stars, they also include a number of counter examples: B8 type stars that are not seen as green but instead as white or bluish-white include the prominent examples Alpheratz, also known as Sirrah, (Alpha Andromedae), which is one of the four main stars composing the square of Pegasus, Gomeisa (Beta Canis Minoris), and the blue supergiant Rigel A which is usually seen as blue or white. (But Rigel is a supergiant not a main-sequence dwarf if that’s significent?)

    * Assuming some of these stars are green, at least to some degree, what could be causing this?

    1. One possible, if maybe rather ad hoc explanation, for why some B8 stars might be prominently green whilst others are not could have to do with the angle they’re viewed from. We already know that many B type stars are spinning extremely rapidly and thus distorted in shape – and that as a result the equators of these stars are darker and their poles hotter and brighter. (Eg. Achernar, Regulus & A0 thus *nearly* B-type Vega.) Maybe this factor is somehow at play here with some stars angled to show their green areas and others not?

    2.Alternatively, perhaps the greenness arises from our seeing spots or patches of metallic elements that we know dapple some stars, for instance Gamma-2 Arietis? (Gamma Arietis as a whole has the proper name of Mesarthim : http://stars.astro.illinois.edu/sow/mesarthim.html ) Chemistry tells us that some elements such as radon, barium, samarium and chromium can create green colouration. (Lapp, Ralph E., ‘Matter’, Time Inc., 1965.) Are there then, perhaps “greening” elements concentrated into starspot-like patches on Beta Librae’s surface?

    3. Another theory speculated for Zubeneschamali’s greenness is that its colouring results from the stars light actually being from a combined ‘blue dwarf & yellow giant seen at right angles’ producing its green~ness. (Clemishaw, “Your Views” in ‘Astronomy Now’ magazine, August 1996.)

    * Zubeneschamali is also a secular or historical variable. If the historical records are accurate, the “secular” variability – the supposed change of apparent magnitude in some stars over historical times – of Zubeneschamali was truly spectacular. Zubeneschamali’s change was from possibly as high a magnitude as zero or brighter equal to Antares in the 3rd century BC down to its current apparent magnitude of 2.6. Could the same factor be behind both the secular variablility and the odd colour of Zubeneschamali? Could it be a thin shell of gas or a shift in chemically concentrated patches on the star?

    Any more ideas or explanations – & does anyone know if the spectrum of Zubeneschamali has been analysed for answers to this puzzle as you may expect would happen?

    NB. Info. here taken & slightly edited to suit from an article I wrote for the SA Astronomical Society Bulletin newsletter (Zubeneschamali : An Emerald of the Sky?, S. Raine, July 1995.)

    – Plutonium being from Pluto aka StevoR.

  10. Tim

    Presumably that assumes something like sRGB colour-space?

    At least I can use that as a palette for my next website design :)

  11. clh

    A technique I found useful is to sample the blackbody spectrum at the red, green, blue and indigo wavelengths (add the indigo back into the red, because the red receptors in the eye spike at both wavelengths), then divide those numbers through by the same numbers for the blackbody spectrum of the sun.

  12. Pi-needles

    @5. drow Says:

    “your eyes can deceive you, don’t trust them.”

    So, on occasion, can your mind play tricks on you and your other senses mislead as well.

    @ 4. Phillip Helbig Says:

    … As Feynman noted, there are no green stars!

    Oh I’m sure some of them are eco-friendly! ;-)

    Would Steven Seagal, REM or Sting count as green stars? ;-)

    & “Colour is as much physiology and psychology as it is physics.”

    Very true. Oddly the colours we associate pyschologically & artistically with “warmth” (red, orange, yellow) vs those we generally associate with cold (white, blue) are actually the exact opposite of what is physically actually the case! Reds are technically *colder* and blues *hotter* but we don’t metaphorically / pyschologically / artistically take them that way. As everyone probably already knew.

  13. I came across this table with HEX colors for tons of star types, you might find it illuminating: http://pnt.me/QIubf4

  14. MoonShark

    I bet just putting these hex colors on a black background (as Phil says) would make a huge difference. Eyes are funny like that. The white of this page is basically light pollution.

    Oddly the colours we associate pyschologically & artistically with “warmth” (red, orange, yellow) vs those we generally associate with cold (white, blue) are actually the exact opposite of what is physically actually the case! Reds are technically *colder* and blues *hotter* but we don’t metaphorically / pyschologically / artistically take them that way.

    Yes, for the scale of blackbody radiation or spectroscopy, which humans don’t experience as much on an intimate basis (scientific knowledge on both is relatively new). But the cultural perception doesn’t seem like a big mystery. The sky and oceans cool your body and appear blue, whereas woodfire and blood are warm & red :)

    So, on occasion, can your mind play tricks on you and your other senses mislead as well.

    Yep, I’m writing a paper for my behavioral genetics class on synesthesia. Some people can not only experience sound or touch hallucinations, but they cognitively mix and match senses as well. E.g. Color-taste, pitch-color, even time-space.

    An example of the latter would be people who (usually not deliberately) visualize months as if they appeared on a geometric shape like a grid or an ellipse. These people consistently perform faster than average when tested to do something like “name every third month starting with October” or “recite the months backward skipping ones that start with J”.

  15. Chris A.

    No doubt in my mind–the reddest of Charity’s colors pale (pun intended) in comparison with the reddest (carbon) stars. Check out R Lep or V Hya at minimum brightness (and thus, maximum redness)–positively crimson!

    This blog entry reminds me of the attempt, several years ago, to come up with the “average color of the universe,” which, at first, was supposed to be a pale green, but then someone realized they had goofed, and it was revised to a sort of beige (#FFF8E7, dubbed “cosmic latte”).

  16. wolfblass

    Everyone knows that Sun’s color is #666699. Recent attempts to colorize it #ff0000 notwithstanding.

    (I apologize for injecting CS geek humor into an astronomy crowd.)

  17. Personally, I’ve never perceived the sun as yellow, at least not when it’s high in the sky. It’s always looked white to me. This might be that I grew up in a scientifically minded household and was told from a very young age that the sun is white and thus I have come to interpret it as such or it could be because my vision is terrible.

  18. Jason

    @7
    I don’t think it is so odd. For much of Human history, and even now in our normal experience warm/hot=red and cool cold equal holds.

    For a significant portion of human history and even now, most heat sources we are likely to have direct physical experience with are going to to be on the reddish end of the spectrum. Yes Gas flames are blue, but they don’t generally heat things to blue-white hot. Additionally we bodies of water as blue and usually cool feeling. Add to that the cultural surroundings that re-enforce the imagery and its no wonder we see things that way. And if you go back in time historically it was even rarer to experience heat at blue-white levels.

  19. Navneeth

    I’m surprised, Phil, at your usage of the word factoid in the vein of many newscasters and the lot of people who generally don’t verify the authenticity of piece of information before claiming it as a fact. ;)

  20. Captn Tommy

    I find this interesting because I had catract surgry and lost the yellow pigmented natural lenses we all are born with… so when I mention the wonderful pink sunset to my wife she quite naturally contradicts me with ‘it’s orange dear’. Which of course I do not see. I refuse to argue back. We sees whats we sees by gumpcha. Aye thats we do!

    enjoy

  21. Charlie Young

    #9 Chris A. maybe that’s why we see beige as a nice, neutral color to paint a room.

  22. Scott de B.

    “I am saying that trying to get hex codes for star colors is like writing down the notes to Beethoven’s Ninth Symphony on paper. It’s a code, and has the right information in it, but it’s not the same as hearing the orchestra.”

    An interesting comment given that Beethoven was deaf when he wrote the Ninth Symphony.

  23. JoBrad

    Very cool.
    You mentioned that we see colors differently based on contrast. Beau Lotto has a very cool TED talk which highlights (in the first 2 minutes) how our brain shows colors in contrast to varying backgrounds. Just in case the URL doesn’t work, it can be found at TED dot com, and is titled: Optical Illusions show how we see.
    http://www.ted.com/talks/lang/eng/beau_lotto_optical_illusions_show_how_we_see.html

  24. Jim Salacain

    I think the reason we perceive the sun as Yellow is that when we look towards it (not at it “Ahhh, my eyes!”) our field of view is filled with the blue of the sky and , because the human visual system is not a colorimeter, tried to drive the perceived scene to a neutral and therefore the perception of the sun is that it is blue’s conjugate, or yellow…

    The other thing that’s interesting about trying to come up with RGB values for blackbody radiators is that color space (that which we perceive) is not two dimensional, but three. Our perception of color changes depending on the intensity of the light as well as our “dark adaptation. ” In the dark we become much more sensitive to red and during in the light, to green. Perhaps this explains why stars seem “more” red through the telescope than on out monitors.

  25. Some of us can look at notes on paper and hear the music. It requires training, however.

  26. jcm

    Are these hexadecimal (hex) colors an accurate representation?

  27. andy

    Interesting point you mention there about Vega being blue. Historically, Vega was used as a reference point, and it seems the description of star colours, in terms such as “red dwarfs” and “yellow dwarfs” seem to be implicitly assuming a system where Vega is white.

  28. What gamut and gamma response? What K white point? These numbers are as meaningless as the red/yellow/blue color wheel.

  29. Mike

    “a whole nuther”
    :(

    OTHER
    OTHER
    OTHER

  30. MikeC

    What fluffy said. Hex values are just device settings. They’ll look different on every monitor. If you want a real color, we need to use an actual color value system, like Lab*.

  31. flums

    Color spaces are pretty complicated things.
    The RGB color space is pretty limited in what it can represent. CMYK has a way bigger range and for example LAB can represent more colors then the human eye. So, don’t wonder if this images looks kinda flat.

  32. Keith Harwood

    Dave Malin, late of the AAO, used to give a talk on star colours. One of the points he made was that the filament in his slide projector was at the same temperature as the surface of a red dwarf and both pretty much black bodies, so what we see with no slide is (almost) the colour of a red dwarf. To us in a darkened room it looked white.

    I suspect that, regardless of what you read in science fiction, on the surface of any planet around a star from M to A, the star would look white. (I suspect that for B and points north the star would be so far away from a habitable planet that it would look like a welding arc and therefore appear blue.)

    One exception would be the M carbon stars. The absorbing carbon pushes the colour a long way from black body and I suspect such a star would look distinctly orange.

    The “almost” above came, Dave said, because there was a heat filter in the projector that he couldn’t remove and that added a faint greenish tinge. I couldn’t see it myself.

  33. MW

    When I was an undergraduate, I had a number of badges I made up by printing them on a (at that time rare) laser printer, sticking them to cardboard and cutting them out. My collection included things like “Religion is Myth Information” (original to me) “Only Bored Astronomers Find Gratification Knowing Mnemonics” (not original.)

    Some of these badges were printed on pastel-coloured paper rather than white. I noticed once when walking home at night (with light only from distant street lamps) that the badge I was wearing appeared white, but I knew it was coloured. I pulled out a bit of white paper and put it next to the badge, and suddenly the badge changed to show its true colour. This was of course all due to my brain’s post-processing of the eye’s data, adjusting its ‘white balance’.

  34. Wayne Robinson

    When we see stars that are seeing (I actually mean twinkling, but I wanted to be able to say “see stars that are seeing”) don’t the colours also change due to the chromatic aberration of the turbulent atmosphere? Ethan Siegal on “Starts With a Bang” had 2 whole posts on why Sirius was on the list of red stars compiled by ancient Greek astronomers, although it is the whitest star around (the Sun excluded).

  35. MRC

    To Steve, I came across a really interesting journal about vision and perception–www.glimpsejournal.com. Back to back issues about the perception of color and space. Really informative :)

  36. Bill Brown

    The color issue extends everywhere. Printing has the same issues. Same with internet.
    Print: Ink, paper, light are all factors.
    Computer: monitor, calibration, color gamut, etc.
    Computers haven’t gotten it dialed yet. But they will.
    Soon they will auto-read all influences, and do color seamlessly.

  37. Jamey

    I visited the referenced site – and dug into the part where it shows a map of the spectrum of the Sum (above the atmosphere) vs. a blackbody curve of the appropriate temperature – and to my eye, they didn’t match *THAT* well – there was a lot of deficiency in the red, and excess in the yellow segment. I did notice, however, that a lot of the data used to compute this stuff was very old – the 2 deg field tables were from the 1930s? Perhaps we could draw better data on the color response curves of the three types of cones (and why doesn’t anyone measure the color responsiveness of the rods? Perhaps humans really *are* tetrachromats, with the fourth primary usually being over-loaded or just averaged in?) using MRI and PET type technologies?

    I wonder just how far from the blackbody spectrum most stars really are – and how much that affects their color. For that matter, does anyone know where I might find RGB hex values to approximate various wavelengths along the monochromatic spectrum? Say every 10 nanometers, or specific emission wavelengths?

    Ahhh, the joys of color – and for more fun, let’s look into *naming* colors in various languages!

  38. Chris Winter

    Perhaps when we get OLED screens on our laptops and monitors, we’ll see star colors displayed more realistically.

    Pi-needles wrote: “Oh I’m sure some of them are eco-friendly! ;-)

    Would Steven Seagal, REM or Sting count as green stars?”

    Ed Begley Jr. definitely would.

  39. JupiterIsBig

    I saw on a documentary that some antives in Madasgascar or maybe Mauritius don’t have a colour orange – it’s all red.
    They didn’t go into whether they don’t see it or the don’t differentiate, or what.

    Of course it was on TV, so who knows if it’s even true.

  40. Mike C.

    “The Sun is White Not Yellow”? My world has been turned upside down by your links once again. Fascinating stuff.

  41. timothyalvin

    I don’t think the Sun looks yellow when you look at it. If you try to (not recommended) it’s just very bright, and overloads all your rods/cones. More the experience of being blinded than any particular color. In other words, people in general are not determining that the Sun is yellow by direct observation.

    However, I think we perceive sunLIGHT as looking yellow, by contrast with outdoor shaded areas which are extremely blue in comparison. This causes people to infer a yellow sun although they cannot determine its color directly.

  42. James McCann

    I will second the loveliness of Albireo especially in a smallish telescope. The brightness, contrast and nearness with the right eyepiece is stunning.

  43. Marcello

    that’s an interesting reading, but i have one doubt.

    while i can generally get how determining the color of stars work there’s something i can’t really grok: how’s the color of the universe determined? and, more specifically, how’s that it turns out to be pink/yellowish?

    ok, didn’t see the link ;)
    here’s the answer: http://www.pha.jhu.edu/~kgb/cosspec/

  44. Johan Stuyts

    Forget about being about to communicate a color to somebody over the internet. Unless somebody has created a color profile for his monitor and converted the image to this color profile, the colors will most likely not look like what they really are.

    I just made a screenshot and pasted it in Photoshop with color management (for the web) enabled. The colors I see in my browser are too pale. And I can’t trust the image in Photoshop because I used hueyPro for creating a color profile. It does a reasonable job but cannot be used to create a high-quality color profile.

  45. Jesper

    Interesting, but it’s not this simple.

    You (or the website you found this on) are pretending that the hex codes of colors are absolute values that exactly define a color. But that ofcourse isn’t true. #ffc690 on my monitor may look completely different on your monitor. Do you have multiple computers (or monitors)? Show a color with a given hex code on both and they will most likely look different.

    Maybe the red colors look less saturated than you expected because of the way your monitor displays colors.

    To make your monitor display colors really accurately, you’ll need a device to calibrate your monitor and you need color management aware software.

  46. Bryan

    There’s also the fact that the RGB color space represents the relative apparent luminance of three wavelengths of visible light within a range. Not only are you not hindered by that range when looking through a telescope, but changing what “100%” means within RGB can have a significant effect on the resultant apparent color.

    Another thing that kinda gets me is that “FF” is used – if your camera’s set up properly, you should only get values from 6% to 94% (Roughly 11 to EE, in hex) for any given pixel. If you’re looking at stars, that implies that, well, the brightest value you should have should be in the range of EE. To see FF’s implies to me that either this color chart was normalized (which doesn’t appear to be the case), or that the “high” value has been clipped to the maximum (i.e., the color has been washed).

  47. -jeffB

    “Another theory speculated for Zubeneschamali’s greenness is that its colouring results from the stars light actually being from a combined ‘blue dwarf & yellow giant seen at right angles’ producing its green~ness. (Clemishaw, “Your Views” in ‘Astronomy Now’ magazine, August 1996.)”

    This is a misconception. Blue light combined with yellow light makes WHITE light; in fact, that’s how “white” LEDs generally are made. “Blue + yellow = green” is only true of subtractive color, not additive color.

    You can’t get green light by combining non-green light sources. You can only get it by starting with light that has a green component, and making sure that green component is dominant, either by omitting or filtering out other colors.

  48. George

    Heliochromology addresses this topic nicely. Ok, it’s not in any curriculum, but it has been a lot of fun, at least for me.

    In a nutshell, unfiltered solar projections, when the Sun is relatively high in the sky, are white… very white. Now think about what colors are missing from these white, terrestrial observations of the Sun’s disk. These missing colors (extinctions) are primarily the blues, with less and less of the greens to reds.

    If you add blue to a white object will it ever appear yellow??? Nope! Will it look green? Nope!

    It’s very, very likely that the Sun will always appear white across its entire disk, assuming we are observing the Sun from space (free from atmospheric effects) and at a greatly reduced intensity.

    What about the Sun having a peak intensity of green? It does and it doesn’t. If you use the Sun’s “effective temperature” (5777K) — the blackbody temperature that radiates the same amount of energy as the Sun’s surface — then the peak for this temperature will be found at 501.6 nanometers (5016 Angstroms). This is just in the green color range. But this will not give us a true color result since the eye will weigh all the other energy levels to produce a net color result.

    Some articles state the Sun is white because white is the result when all the colors of the visible spectrum are present. This is incorrect as all stars radiate across the visible spectrum. Color is simpy the product of the spectral irradiance of the object and the spectral sensitivity of our eye. The entire spectrum must be weighed in order to determine the color.

    Some have said the peak is in the yellow. It is but it isn’t. If one converts the spectral energy values to a spectral photon flux, then, for some data sets, the peak is in the yellow, surprisingly. But it ain’t a peak; it’s a pimple! Once again the color observed requires weighing the entire photon flux of the visible spectrum. In this case, our Sun has a very flat photon flux distribution, which may be a nice way to define white as a color, ignoring the semantic issues.

    For almost daily sp. irr. data go to SORCE….http://lasp.colorado.edu/sorce/index.htm
    [The peak wavelength of the Wehrli ’85 data set is 450.5 nm, which is bumping into the violet! But this is a smaller pimple than the photon flux pimple.]

    Here is a fun blog on this topic that I hope yyou will like…
    http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_revelation

    The bautforum has many threads on this colorful *cough* topic.

    George, your friendly neighborhood heliochromologist

  49. Jamey

    Oddly enough, I’ve often thought it was – roughly speaking – a matter of combinations. All cones fire = white, no cones fire = black, primaries are one type of cone peaking, secondaries are two kinds of cones peaking.

    Tetrachromacity would be interesting, then – White, 4 primaries, 6 secondaries, 4 tertiaries, and black… What a strange view of the world!

  50. Plutonium being from Pluto

    @ 47. -jeffB Says:

    “Another theory speculated for Zubeneschamali’s greenness is that its colouring results from the stars light actually being from a combined ‘blue dwarf & yellow giant seen at right angles’ producing its green~ness. (Clemishaw, “Your Views” in ‘Astronomy Now’ magazine, August 1996.)” This is a misconception. Blue light combined with yellow light makes WHITE light; in fact, that’s how “white” LEDs generally are made. “Blue + yellow = green” is only true of subtractive color, not additive color. You can’t get green light by combining non-green light sources. You can only get it by starting with light that has a green component, and making sure that green component is dominant, either by omitting or filtering out other colors.

    Fair enough. Scratch that hypothesis then. ;-)

    I wasn’t necessarily condoning that idea just mentioning it as something that’s been suggested. I had also figured that it was an unlikely explanation because you’d think it would show up in the spectrum and other traits of Zubeneschamali somewhere anyhow were it true.

    Thanks for that though. :-)

  51. Gary Ansorge

    25. feralboy12

    For some people(like me or Phil Lesh) music is also a visual phenomena. It’s referred to as synesthesia(incorrectly, in my opinion, since I just interpolate the music visually. Don’t know about Phil). Personally, I think it makes music really cool.

    Gary 7

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