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No Night Darkness in the Infrared

Human beings perceive objects by seeing in the "normal" optical range. This is purely an evolutionary imperative. Evolution could just as easily given us eyes that work in the infrared to know what is going on around us. If this was the case we would experience no night at all. The night sky would be just as clear as the sky in the day.

At night the sky would be lit by hydroxyl molecules emitting infrared light in the form of a mass of narrow emission lines. It would be like daylight, though a few stars could be seen along with the Sun and the Moon.

Telescopes operating in the infrared get over this problem by using limited apertures and special filters. These filters use a photonic lantern system to move the light into parallel tracks. A Bragg filter reflects out the tracks and lets wavelengths between lines through. Many IR telescopes are in space where such a filter is unnecessary. The space telescopes beam data back to Earth.
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