Danjon scale

The Danjon scale is a five-level scale for the classification of the color and brightness of lunar eclipses, which depend only the geometric properties of darkness by the current conditions in the Earth's atmosphere. The scale readings are no physical basis but the corresponding value is estimated by the observer. It was proposed by André- Louis Danjon and is now named after him. The value of the Dajon scale is designated by the letter L.

The scale

The scale is defined as follows:

Determining the value

Determining the value of L is best carried out to the middle of the dark with the naked eye. The determined value is subjective and different observers may come to different results. In addition, the brightness of different areas may vary and correspond to different values ​​of L, because the brightness depends on the distance from the axis of the shadow.

Factors that affect the value of L

Many factors can affect the appearance of the moon during an eclipse. What is important is how central the Earth's shadow hits the moon. However, the current conditions in the atmosphere are important. At locations where no direct sunlight reaches the moon's surface, is some light that is refracted in the atmosphere, to the moon and gives it a reddish tinge.

The amount of light that passes through the refraction of the moon affects the brightness during the total eclipse. This depends on various factors. Volcanic eruptions are one of the most influential effects. Volcanic eruptions that release large amounts of ash into the atmosphere, have very dark red for a few years eclipses result. The impact of the eruption of Mount Pinatubo was the world very pronounced and so the lunar eclipse on 9 December 1992 with a value of L = 0 was evaluated on the Danjon scale.