May 12, 2009
A birthday is what happens when cosmic time briefly puts down the scale of eons and pays attention to a single human year.
A Circumhorizontal Arc Over Ohio
Birthday · May 12, 2009
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APOD published May 12, 2009. Credit: Todd Sladoje. A publication-date match, not a photo taken on your date. Independent of NASA.
Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio last week. Apologies: Earlier, APOD misidentified this phenomenon as iridescence.
Image credit: Todd Sladoje