Color-Challenged Astronomers Are Lost in a Latte' Universe

God was sitting up late one night designing the universe. He took care of simple things first. Gravity would construct stars, galaxies and planets. Biological evolution would ensure a robust diversity of life forms.

But what color to make the universe?  God looked down into his foamy cup of latte' and decided that the color beige would be just perfect. In reality God hadn't invented the other colors yet so He didn't have much of a choice at the time.

Last Monday the Astronomy Picture of the Day displayed nothing but a plain eggshell white panel. The caption declared that is how the entire sky would look if the light from all the stars and galaxies were smeared out into a homogeneous glow.

This snoozer-looser of a color interpretation was first popularized in 2002 by Karl Glazebrook of The Johns Hopkins University. He based “beige” on averaging the color spectrum of the light emitted by a whopping sample of 200,000 galaxies in a sky survey.

When the notion that the universe had a Pantone color was first popularized, the news media loved it. This was one of the biggest novelty stories ever to come out of astronomical research. It was a cinch to sell to science-adverse newspaper editors, and there were many popular articles.

But beige is not a color found in the rainbow. You don’t buy beige filters for your SLR camera. In looking at Hubble Space Telescope’s colorful photos of the universe we’ve never said, “it needs more beige!”

Color, by definition, is really all in the mind. Three sets of color receptor cells in the retina each cover 1/3^rd of the visible spectrum and assemble a full color image in the brain's vision center. The three additive colors parsed by the eye -- red, green, and blue -- create every hue perceived in the universe.

The problem is that many astronomers are color-illiterate according to my colleague Ken Brecher of Boston University. Any art or photography student will describe color as having three dimensions: hue, shade and intensity. But to an astronomers color is simply a matter of the wavelength where visible radiation falls on the electromagnetic spectrum.

An astronomer himself, Ken can be found at astronomy conferences doing impromptu floor demonstrations of how we perceive color and how easily it is misunderstood, even by inquiring minds.

Beige is only a desaturated yellow. It is produced by subtractive colors: the pigments cyan, magenta and yellow that are mixed together and reflect only certain wavelengths of light. So you’ll find beige in the Home Depot paint aisle, or a Crayola box of crayons, but not among the stars.

This color-illiteracy is painfully obvious in any number of space illustrations that show red giant or red dwarf stars as, well, cherry red. Wrong! Though the brighter stars have a perceptible hue when seen as points of light. But if viewed close up they would all be blindingly white. Why? Because a star is radiating across the visible spectrum and the intensity of light would be so bright it would fire up all of your color receptors.  hence the brain would perceive white. What's more, our sun's output peaks in the green portion of the spectrum, but that's meaningless when it comes to human color perception. 

The term “brown dwarf” is just as misleading. Brown’s another color not found in the radiant universe. In the world of pigments, it’s a desaturated orange. A better term for these stillborn stars in "ultra-red dwarf."

Glazebrook was simply trying to give an everyday interpretation to his cumulative spectrum of stars.  On a graphical plot average starlight color rises slightly at longer wavelengths because the quantity of blue stars is decreasing as the rate of star formation throttles back in an aging universe. Hence he says the data show the universe is evolving from blueish to caramel.

But the homogenized stellar spectrum is much flatter or “whiter” than that of an incandescent light bulb for example, which steeply rises to peak output at red wavelengths. Therefore, if a light bulb doesn’t look beige, neither does the universe. The sum of starlight is, perceptually, white.

But don’t feel so bad about losing “cosmic latte'.” Glazebrook’s initial interpretation of the survey data lead to a press release that reported that the universe was an Smurfee turquoise. The New York Times even ran a pistachio blue-green color patch on the front page to announce the "official" color of the universe. 

Yuck! How could God ever have such bad taste!