|How Many? A Dictionary of Units of Measurement
© Russ Rowlett and the University of North Carolina at Chapel Hill
Lunar eclipses differ greatly in appearance, because varying amounts of light are refracted or scattered into the Earth's shadow by its atmosphere. The darkest eclipses occur when clouds of volcanic ash high in the atmosphere block most of this light. The following scale, intended for visual observers, was designed by the French astronomer André Louis Danjon (1890-1967).
Source: Danjon Scale of Lunar Eclipse Brightness, posted by the U.S. NASA Goddard Spaceflight Center.L = 0 Very dark eclipse. Moon almost invisible, especially at mid-totality.
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May 15, 2003