Last week, astronomers released an arresting color picture of a pair of colliding galaxies, combined from separate images from three of NASA’s Great Observatories in space.

The picture looks too good to be real. Or is it?

SLIDE SHOW: NASA’s Hubble Space Telescope has snapped images from the far corners of the known universe. Take a look at our favorite Hubble images of 2009.

This is the most common question I get in e-mails and from audiences in science presentations. An urban legend has developed over the years that the colors in modern astronomical photos are made up in a paint-by-numbers game by publicity-hungry astronomers.

 True, if you’ve ever had an opportunity to look at a nebula through an amateur telescope it looks like a gray cotton ball rather that a vibrant tie-dye composition.

Despite what you see in lavish Hollywood sci-fi movies, even if you could warp-speed out to a nebula it would still look grey. Why? Because the light from glowing gasses would be spread all over the sky and hence remain too weak to trigger our eye’s color receptors.

You can easily convince yourself of this by simply looking at the Milky Way on a clear night and comparing it to a published color photo taken with a consumer camera. The photo shows brilliant blue star clusters and pinkish nebulae.

Collecting and analyzing these colors is one reason we go to the expense of building huge telescopes. They tremendously amplify our vision by orders of magnitude.

In this age of digital photography — where your cell phone camera does all the thinking (save for the photo’s composition) it’s easy to forget that photography is a science and not just an art.

What’s ironic is that as consumers we shop for the richest, most vibrant HDTV flat panel displays, computer monitors and cameras. Every one of these color technologies dissects the light into component colors and puts it back together. Therefore they all electronically create a color facsimile of the real world.

The way telescopes collect and assemble color information is fundamentally no different from consumer devices. Astronomers simply have to do it manually when it comes to astrophotography. Why? Because telescopes do not have color cameras. Instead, they use black and white detectors that are more accurate, sharper, and more sensitive than a comparable color camera detector.

This is no different in concept than the Techincolor motion picture process that Hollywood perfected in the 1930s. All the cinematography was recorded on sharp black and white film and then optically filtered and printed onto color film stock to ensure color fidelity.  Nobody has ever questioned Rita Hayworth’s true skin color.

When images are combined astronomers take great effort to preserve the integrity of the information collected from far-flung objects. As with the Technicolor process, the color corresponds to the filters used for the initial set of exposures.

Biological evolution figured this process out long ago. The brain assembles a full color image with millions of hues from signals independently sent by three different types of receptor cells in the eye’s retina.

Many celestial pictures look garish because the universe is, well, garish. Hot gaseous clouds of hydrogen, helium, and oxygen glow with the same intense color saturation you would see on nighttime stroll down the Las Vegas strip.

The best astrophotography is comparable to Ansel Adams’ nature pictures.  Adams worked to extract the maximum information and quality from his photographs.  This required many hours in the darkroom for Adams to reconstruct an image that reproduced the broad tonal range and contrast that our eye perceives on a sunny day.

Astronomical colors today get even more problematic because space-borne telescopes like Chandra and Spitzer see in X-ray light and infrared light respectively. Infrared pictures would be pretty dull if the Spitzer astronomers made them all look a deep blood red. So the broad spectrum from red to green to blue is mapped into Spitzer images – from long to shorter infrared wavelengths.

Besides making pretty pictures, when all this spectral information is properly combined it yields new insights into the nature of the objects.

So sit back and simply enjoy the natural beauty and wonder of the cosmos. We are privileged to live in a time when a marriage of computers, digital imaging and powerful telescope empowers us with a God’s-eye view of the heavens.