Fanning the Flame

A fan’s blade passes through the hot air rising above a flame in this iconic image by high-speed photography pioneer Harold Edgerton. This photo uses an optical technique known as schlieren photography that makes density differences in transparent media like air visible. Because of its lower density, the hot plume of air above the flame rises. When the fan blade swings past, it sheds a vortex off its tip and the rising air from the flame gets pulled into the vortex to make it visible. To the left, a ghostly counter-rotating vortex sits on the opposite side of the fan blade. (Photo credit: H. Edgerton and K. Vandiver)

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