If Brown Isn’t a Color, What Color are Brown Dwarfs?


We’ve talked about brown dwarfs here on Universe Today for years and years. These are the “failed stars”; objects with too little mass to fully ignite nuclear fusion in their cores. Instead of blazing with red, yellow or the white light of our own stars, they’re heated by the gravitational collapse of material. They’re called brown dwarfs, but you might be surprised to know that they aren’t actually brown. In fact, it’s impossible to have brown light. So what color are they?

The term “brown dwarf” was originally coined by Jill Tarter in 1975 to describe these objects, and there were other suggestions for names, like planetar and substar. But the name “brown dwarf” stuck. And here’s the problem, as described by Jill Tarter, “it was obvious that we needed a color to describe these dwarfs that was between red and black. I proposed brown and Joe (Silk) objected that brown was not a color.”

Brown isn’t a color?!

Not for astronomers. When they consider the color of a star, astronomers are talking about the wavelength of the light being emitted. Stars emit light at various wavelengths, and whatever photons are mostly being emitted are what we see. Yellow stars emit primarily yellow photons, red stars emit mostly red photons, etc. But you can’t have a star emit brown photons because the “color” brown is a de-saturated yellow. Brown dwarfs can’t be brown because it’s impossible to emit brown light. So what color are they?

Dr. Kenneth Brecher is a professor at Boston University and the primary investigator for Project LITE. This is a research project that uses a variety of experiments to understand how people see color. I highly recommend you check out the Project LITE website and take a look at the Flash experiments they have available. You’ve probably seen some of these optical illusions in the past, where spinning wheels of black-and-white can actually create different colors in our brains. Brecher demonstrated one of these color wheels for me – it’s a CD that can spin like a top. At rest, you see black-and-white, and then spin up the disk and you can see red, green and blue. Very cool stuff (totally unconnected from the color of brown dwarfs).

The color of a brown dwarf
The color of a brown dwarf

Brecher did a presentation at the American Astronomical Society Meeting about the actual color of brown dwarfs. He even had a flashlight that shines a light the color of brown dwarfs. Unfortunately, I didn’t catch a photo of it, but check out Nature’s blog, they got one. It’s sort of a dull orange color. But here’s the cool part. There’s no way to actually see the color of a brown dwarf unless you’re having the photons strike your eyeballs.

All you color theory folks might want to know the hexidecimal code: EB4B25. And here are the RGB values: R-235, G-75, B-37

So what color would an isolated brown dwarf look like? Dr. Brecher had a slide in his presentation that shows the color – we’ve extracted it and made it bigger. I think it looks kind of reddish orange, but then color is in the eye of the beholder.

17 Replies to “If Brown Isn’t a Color, What Color are Brown Dwarfs?”

  1. Oliver X: You’re right. Laymen would be confused by this article precisely because brown *is* a color, i.e., an artifact of human perception, a psychoneurological phenomenon. However, it *isn’t* a wavelength of light, i.e., *not* a spectral color. The color of something is due to the reflected light you receive from it after various wavelengths of incident light have been absorbed by that thing. Hence green, magenta, and cyan are the primary hues of light, while lavender, yellow, and chartreuse are light’s secondary hues; but red, blue, and yellow are the primary colors *as we see them, due to absorption of other wavelengths by objects we look at*, and green, orange, and purple are secondary colors. (BTW, purple is *not* a spectral color, though violet is; yet you’ll find both in one of the larger sets of Crayola crayons, which are compounded to conform to our color sense, and not to pure spectral colors. So: brown *is* a color — but not a spectral hue.

  2. Careful with your terminology here. There obviously are “mixtures of photons that can produce light that looks brown to our eyes”. Otherwise we would never see anything that was brown.

    I think the issue here is that astronomy has a simple “one-dimensional” notion of color which is simply “the dominant visible spectral wavelength”.

    This has very little relation to our everyday human notion of color which has three independent components. The components are derived from the receptivity of our three different types of photoreceptors to different parts of the spectrum.

    There’s no meaningful way to translate our notion of brown (partly greenish, partly reddish, a bit of bluish) to the astronomical notion of color (ie dominant wavelength of ~700nm, also known as red). If the color is not “in the rainbow”, it’s not a spectral color.

  3. Stars as hot as the Sun or hotter have very little if any molecular compounds in their photosphere and are close to being blackbody radiators, which limit their color range from bluish-white, to white, to a yellowish-white, to orange, perhaps orange-red for carbon stars.

    However, this is certainly not the case for brown dwarfs. The organic soup of these objects may and do alter their SED (spectral energy distribution) allowing brown to be a strong candidate for their color.

    I sure do like the site you linked to, Frasier. Thanks.

  4. In April of 2006, I was able to see DENIS PJ1441-0945, a 20th magnitude binary brown dwarf in Libra, with my 32″ reflector. This may have been the first visual sighting of a brown dwarf. I’ve been able to spot three others since then, but none have shown any hint of color, of course.

  5. quote:
    “But you can’t have a star emit brown photons because the “color” brown is a de-saturated yellow.”

    Sorry for nitpicking, but brown is not a de-saturated yellow. It’s dark yellow, or dark orange, or dark red. If yellow is 100% red, 100% green and 0% blue, then brown would be something like 50% red plus 50% green to 90% red plus 10% green, with blue at 0%. This color is still fully saturated though.

    Provided you wish to keep the lightness, de-saturation of yellow would mean adding twice as much blue as you take from green and red respectively. For instance 80% red, 80% green and 40% blue would be a de-saturated yellow and it would look something like light olive.

  6. If you look at sensitivities of the eye’s L, M, and S (Long, Medium, and Short wavelength) primaries, then you might think that the longer wavelengths would favour the L receptor. In fact, for wavelengths below 700nm, the sensitivity of the L recptor is falling off faster than the M receptor, so the colour we see is no longer a deep read but starts going back towards orange a bit. I have looked at wavelengths from 600nm to about 720nm in the dark, and I have seen it. If you want more on this phenomenon, see Lamb’s chapter from ‘Colour Vision’ (Gegenfurtner & Sharpe).

    Nevertheless, this exotic effect aside, as an object cools, the light it emits will go from orange to red, and then will go to a dimmer and dimmer red. If you were close to a brown dwarf and could see it as a disc, then it would be pretty dim even if it was acting as a perfect blackbody. It would be hard to spot by its own light. Probably this is why the artist added other stars nearby to light it.

    Giving the colour match as an RGB triplet is not brilliantly accurate if the colour is well off neutral. Most displays have a tone curve that departs from a uniform gamma at the bottom end, and CRTs and LCDs depart from gamma in different ways. However, in an imperfect world, it does give the right sort of dirty orange colour.

    I like the term ‘brown dwarf’. It will give off a very dull red glow. The red won’t be a deep LED red, but something duller and more orange. We want a word that describes an unexciting orange color, but it must also stress the low intensity. The word ‘brown’ comes about as close as we can get without having to invent another word. In fact, we are sort-of inventing a new color term because we are applying it to an emissive colour rather than a reflective one. ‘Brown’ also carries connotations of ‘brown-out’ – of something not working properly because there isn’t enough power, and so forth. The first time I met the term ‘brown dwarf’ I understood it straight away – I doubt if I would have done the same with ‘planetar’ or ‘substar’.

    We control words, not the other way around. Let there be brown light!

  7. Wow.

    I’m shocked that anybody wearing a tin foil hat has yet to comment on the supposed “brown” dwarf orbiting our Sun and how it’s being steered by advanced beings on a crash course with our planet. 😉

  8. When I look at the orange square in the article with eyelids only slightly ajar, or when I dim the monitor, I see it just nicely brown. So it in fact does not deny the “brown dwarf” definition, it confirms it.

  9. Brown is not a defined color. Basically it is any hue that is low saturated. One can say Red brown, Yellow brown, Green brown, Orange brown. Blue brown tends to be grey as well as purple brown. What color is is brown or grey? Have you ever tried to match clothes at a store? The words brown or grey do not really discribe any color, only its low satuation.

  10. if an object orbits a brown dwarf, as in the artist’s concept, is it a planet or a moon?

  11. Again, what Oliver X said. If brown is not the color of a vintage Fender Bassman amp, there is no universe!

  12. From Artist point of view…It is every color but ‘Brown’. ‘Brown is the ‘hue’ being reflected back to your eye. All other colors or wavelengths are being absorbed in the object. Just like a blue object is not blue. It is absorbing every ‘color’ but blue, and is reflecting blue back to your eye. When I got into fine art painting, I had to figure that one out to understand how to ‘mix’ the proper hue of colors I wanted. Either I have stumbled upon twisted logic, or my thinking is just different.

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