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Color Our World

Astronomers pinpoint true hue of the universe

TUESDAY, Jan. 15, 2002 (HealthDayNews) -- It's not the color of money or the Color Purple. It's more of a greenish purple.

That, according to astronomers, is the true color of the universe.

Researchers at Johns Hopkins University have been having some fun in the research lab. By combining the average value of all the light in thousands of galaxies, they have determined that the overall color of the universe lies somewhere between "medium aquamarine" and "pale turquoise."

Mind you, this is not an actual color you would be able to see from some special, far-distant vantage point in space. It's just the color you would see if all the visible light in the universe could be viewed together.

"It's the color you'd see if you could see all the nearby universes in one go," says Ivan Baldry, one of the researchers and a postdoctoral fellow at Johns Hopkins University. "That represents the average spectrum of universe."

Over the course of evolutionary history, the human eye has adapted to a very limited band of the particular spectrum of light our star, the Sun, produces.

As a result, the average human eye can only see a specific range of colors between red and violet, experts say. Anything outside that spectrum is invisible to us.

You can, however, see the effect of the sun on color if you go scuba diving: The deeper you go, the more monochromatic the scenery becomes. That's because light waves that fall in certain parts of the visible spectrum are unable to penetrate an increasingly thick curtain of water.

"Our eyes are accustomed to seeing the sunlight, which is why we see the range of wavelengths we do around red, yellow, green and blue," says Baldry. "Conceivably, if we lived near another star, then our eyesight would evolve in a different way."

Any life that may exist in other star systems would presumably also evolve to take advantage of the specific spectrums their own stars produced.

In other words, what's visible to us may not be visible to others from an alien world. Sorry, "Star Trek" fans.

For this experiment, Baldry and Karl Glazebrook, an assistant professor of astronomy in the Krieger School of Arts and Sciences at Hopkins, combined 500 individual colors, everything from red to a tiny bit of ultraviolet that cannot be seen by the human eye.

They then took this "cosmic spectrum" and used a computer to determine how the human eye would perceive all the light. The researchers presented their findings last week to the American Astronomical Society.

There actually was a serious intent behind the work: the researchers were using colors to get information on star-formation rates.

"The cosmic spectrum gives us information about what types of stars are present in today's universe," says Baldry. "It's telling us that we're at an age where the number of stars forming is declining, so most of the stars [that ever existed] formed between five and 12 billion years ago."

Judging from the data, the Hopkins astronomers say, the universe probably started with a "blue period," which took its color from the preponderance of young blue stars. A "green period" ensued as the number of older red stars increased. Upcoming is a "red period," as older, redder stars dominate the celestial canvas, they add.

What To Do

To see the color of the universe on your computer, go to Karl Glazebrook's home page at Johns Hopkins University and scroll down to the third illustration.

Check out Universe Today for the latest scientific news on happenings in the universe.

SOURCE: Interview with Ivan Baldry, Ph.D., postdoctoral fellow, Johns Hopkins University, Baltimore; Jan. 10, 2002, Johns Hopkins University press release
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