Seeing Red at Kitt Peak

This image captures the Milky Way arching above a pair of telescopes at Kitt Peak National Observatory, a Program of NSF’s NOIRLab. The Nicholas U. Mayall 4-meter Telescope (right) and the UArizona Bok 2.3-meter Telescope (center) jut above the desert skyline, outlined by the subtle colors of airglow. As well as the spectacular night sky, the red lights illuminating Kitt Peak lend further color to this image. 

These red lights are not simply for aesthetic purposes. When you are in a dark environment, your eyes gradually become accustomed to the low-light conditions. This process is called “dark adaptation,” and it can take up to two hours for your eyes to fully adjust to dark surroundings. Bright white lights — like those in regular streetlights — can undo dark adaptation within seconds. Redder wavelengths of light don’t have such a detrimental effect, and red lights are therefore used at Kitt Peak to help astronomers find their way, while preserving their dark-adapted eyesight.