Red Cloudbow over Delaware.

What kind of rainbow is this? In this case, no rain was involved -- what is pictured is actually a red cloudbow . The unusual sky arc was spotted last month during sunset in Rehoboth Beach , Delaware , USA . When the photographer realized that what he was seeing was extraordinary, he captured it with the only camera available -- a cell phone. Clouds are made of water droplets, and in a cloudbow a cloud-droplet group reflects back light from the bright Sun (or Moon) on the opposite side of the sky. Similar phenomena include fogbows and airplane glories . Here, the red color was caused by atmospheric air preferentially scattering away blue light -- which simultaneously makes most of the sky appear blue . A careful inspection reveals a supernumery bow just inside the outermost arc, a bow caused by quantum diffraction .

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