Is brown a color?

An amusing question for those who like to think about primary vs. secondary qualities, an issue that caused a bit of nuisance for astronomers.

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?

Saturation is at least an objective feature of the spectrum, having to do with how much of it is spread into other colors.  As the Wikipedia entry on “brown” shows, what appears brown to us also depends on the contrast of neighboring colors.

3 Responses

  1. This is really interesting stuff, Bonald. You should post about astrophysics more often.

  2. Is grue a color? Голубой? синий? pink?

    What is meant by “to be a color?” Clearly, not solely to be a trait of all things that reflect light at a single numerical wavelength, or within a single range of wavelengths.

  3. Eh, given that astronomy already defines some common words in uncommon ways (“metal” springs to mind, as well as “black hole”)), using brown for “brown dwarfs” doesn’t seem out of line.

    Heck, blue stars are pretty far from what would be called “blue” in other contexts, too.

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