Danjon Scale - Factors Affecting The Value of L

Factors Affecting The Value of L

Many factors can affect the appearance of the Moon during a lunar eclipse. The Moon's path through the Earth's umbra is important, but so too are the current conditions of the Earth's atmosphere. While the Earth's shadow blocks any direct light from striking the Moon during a lunar eclipse, some light is refracted through the Earth's atmosphere giving a Moon a red hue.

The amount of light refracted affects the brightness of the moon at mid-eclipse, and this depends on several factors. Volcanic eruptions are one of the most significant - eruptions which spew significant amounts of volcanic ash into the air are generally followed by several years of dark, deep red eclipses. The effect of the eruption of Mount Pinatubo on subsequent lunar eclipses was very noticeable, with the eclipse of 9 December 1992 rated 0 on the Danjon Scale by many observers.

It is also thought that the solar cycle has some effect on the darkness of lunar eclipses.

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