Depicting the Colors of Space

The large Whirlpool Galaxy, left, is known for its sharply defined spiral arms.

The Cat’s Eye Nebula — a dying star in the constellation Draco — may appear in images in psychedelic shades of pink and green or in soothing tones of beige and aquamarine. But scientists apply more than artistic license when it comes to assigning colors to distant cosmic bodies that are telescopically photographed.

“The colors we see in images are real colors in the sense of what’s blue is really blue out there; we just might not be able to see it with our eyes,” said Zoltan Levay, who is part of the imaging team at the Space Telescope Science Institute that processes many of the Hubble telescope’s photographs.

Telescopes take photos similar to the way normal cameras do. In place of a lens, telescopes rely upon a mirror that collects light and focuses it onto a detector. In a standard camera, detectors break that light into three colors. But this comes at the expense of image resolution. To retain as much detail as possible, telescopes operate only in black and white. Astronomers take multiple photos using different filters that collect light from the entire range of the spectrum, including areas undetectable to the human eye. From there, they combine the images, which can be used to create a colored photo based on the parts of the spectrum each filter represents.

Even then, the assigned colors serve specific purposes, like bringing out a nebula’s chemical structures or improving visibility in light and dark areas.

“In general, we boost the colors quite a bit to bring out the features we’re seeking,” Mr. Levay said. “But we don’t make this stuff up — the colors are real.” 

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