Alien skies in a beam of light
And when we find life, how will we know? The answer has a lot to do with rainbows. As Isaac Newton recognized, white light shot through a prism (or through curtains of mist seen with the sun at your back) is exposed for what it really is: a band of color spanning violet to red, characterized by "wavelength." Chemicals and gases in the atmospheres of planets can absorb certain slices of this band, called a spectrum, and leave behind a narrow black gap.
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