The Evolving Universe

Smithsonian Institution

Are the colors in these photos real?

True color image of Whirlpool Galaxy and false color image of Star Cluster Westerlund 2

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Yes...

Photographs taken by visible light telescopes are called true-color images. The colors in the photo look just as they would if we could see them in person.

Maybe...

Sometimes, images are corrected to enahnce certain details, much as we correct family snapshots to eliminate red-eye or increase contrast.

And No...

What we see in the X-ray and infrared images taken bu the Chandra X-ray Observatory and the Spitzer Space Telescope is invisible to human eyes. Astronomers assign colors that we can see by moving the X-ray and infrared colors into the range of visible light for these false-color images.

Relatively lower energy light, often from cooler objects, is usually assigned the color red. Higher energy light, often from hotter objects, is assigned blue, and light with intermediate energies is assigned green. The colors are then merged in the usual way to form the array of colors we see in false-color images.

What would it mean to show you an image in true X-ray colors? Your eye couldn't see anything. By shifting the colors systematically to frequencies we can see, while keeping their relative colors constant, we retain a sense of what X-ray color would be like. It's exactly the same as taking a musical tune and playing it in a different key several octaves lower: the sounds (colors) are different but the tune is the same.