Danjon scale
The Danjon scale is a five-point scale for the classification of the color and brightness of lunar eclipses , which depend not only on the geometric properties of the eclipse but also on the current conditions in the earth's atmosphere. The scale is not based on any physical measured values, but rather the corresponding value is estimated by the observer. It was proposed by André-Louis Danjon and is named after him today. The value of the Dajon scale is denoted by the letter L.
The scale
The scale is defined as follows:
| Value (L) | description |
|---|---|
| 0 | Very dark darkness. Moon almost invisible, especially towards the center of totality. |
| 1 | Dark darkness, gray to brownish in color. Details can only be seen with difficulty. |
| 2 | Dark red or rust-colored darkness. Very dark central shadow, while it becomes relatively light on the outside. |
| 3 | Brick-red darkness. Outer shadow usually has a light or yellowish edge. |
| 4th | Very bright copper-red or orange darkness. The outer shadow has a bluish, very light edge. |
Determination of the value
The determination of the value of L is best done with the naked eye in the middle of the darkness . The determined value is subjective and different observers can come to different results. In addition, the brightness of different areas can vary and correspond to different values of L, since the brightness depends on the distance from the shadow axis.
Factors affecting the value of L.
Many factors can affect the moon's appearance during an eclipse. It is important how centrally the earth's shadow hits the moon. But the current conditions in the earth's atmosphere are also important. In places where no direct sunlight reaches the moon's surface, some light that is refracted in the earth's atmosphere comes to the moon and gives it a reddish tinge.
The amount of light that gets to the moon through refraction affects the brightness during total eclipse. This depends on various factors. Volcanic eruptions are one of the most influential effects. If large amounts of ash are released into the earth's atmosphere, they result in very dark red eclipses for a few years, such as the eruption of the Philippine volcano Pinatubo in 1991. The following total lunar eclipse in December 1992 was extremely dark and had values between Rated 0 and 1 on the Danjon scale. When the Pinatubo erupted, large amounts of dust had reached the stratosphere , which also caused impressive twilight phenomena worldwide.
Individual evidence
- ^ Neil Bone: Observing Meteors, Comets, Supernovae and other Transient Phenomena. Springer Verlag, London 1999, ISBN 1-85233-017-1 , p. 87f ( Google books )
Web links
- Danjon's original publication Relation Entre l'Eclairement de la Lune Eclipsee et l'Activite Solaire