BALTIMORE, March 7 -- The universe has come in for a color correction, and home decorators may approve.
Astronomers who announced in January (see http://www.photonics.com/XQ/ASP/url.readarticle/artid.89/QX/readart.htm) that they'd determined the color of the universe will publish a paper on their broader results in April. When they do, the footnote describing the color of the universe finding will cite beige, not the originally announced turquoise.
"It's our fault for not taking the color science seriously enough," said an apologetic Karl Glazebrook, an assistant professor of astronomy in the Krieger School of Arts and Sciences at The Johns Hopkins University. "I'm very embarrassed. I don't like being wrong, but once I found out I was, I knew I had to get the word out."
Glazebrook noted that before the color finding's odd nature led to widespread public interest, it was originally just a footnote to a comprehensive survey of the spectrum of light emitted by 200,000 galaxies. He and co-author Ivan Baldry, a Hopkins postdoctoral fellow, had set out to simply compile a "cosmic spectrum" based on data gathered by the Australian 2dF Galaxy Redshift Survey.
The cosmic spectrum initially took the standard scientific form of a graph, but researchers then transformed it into an array of colors, replacing each wavelength with the color the human eye sees at that wavelength and varying the intensity of the color in proportion to that wavelength's intensity in the universe. Glazebrook said he decided on a lark to try to calculate how the spectrum would appear to a human eye -- to determine, in essence, what color the universe would appear to be to someone "standing" outside it and seeing all its light. The answer: a color a few percent greener than pale turquoise.
Shortly after the turquoise finding made news, Mark Fairchild at the Munsell Color Science Laboratories at the Rochester Institute of Technology in Rochester, N.Y., contacted the Hopkins astronomers. Fairchild and his colleagues helped the Hopkins astronomers determine that
the freeware computer program they'd used to calculate the color of the universe had inappropriately set a feature known as the "white point." The white point is the point at which light appears white given the environment in which the light is viewed.
"Tungsten lights, for example, can make the white point a little bit yellowish," explains Francis Imai, a senior color scientist at Munsell. "Some monitors have a bluish-white point. Your visual system tries to adapt, so that you assume that color is white, but it's actually yellowish or bluish."
Fairchild literally wrote the book (Color Appearance Models, Addison-Wesley, Reading, Mass., 1998) on determining how colors appear to the human eye.
"As it turns out, if you look at all the light in the universe from a room that has a red neon light, then it may appear turquoise," joked Baldry. "But that's not a standard perspective."
With the white point adjusted to calculate the perceptions of an observer looking at the light in a darkened environment, the color of the universe came out beige. When the viewing environment was adjusted to daylight, the color was a faint red; in indoor light, the color shifted to blue.
"The spectrum data's up on our site" (www.pha.jhu.edu/~kgb/cosspec/), said Glazebrook. "Anyone is welcome to try to calculate the color."
A conclusive resolution may have to wait for this summer. Imai says the Munsell Color Laboratories have tentative plans to put together a lab that will let them generate with scientific accuracy the wavelengths of the color of the universe. Then they can put humans in front of the light and get a final opinion.