Editing Danjon scale

{{Short description|Measurement of appearance of lunar eclipse}}
{{citations missing|date=August 2008}}
[[File:Tom Ruen - Lunar eclipses in 2003 (pd).jpg|thumb|right|300px|Two total lunar eclipses in 2003. Their ratings on the Danjon scale would be roughly 2 (left) and 4 (right).]]

The '''Danjon scale''' is a five-point scale useful for measuring the appearance and luminosity of the [[Moon]] during a total [[lunar eclipse]]. It was proposed by [[André-Louis Danjon]] in 1921, when postulating that the brightness of a lunar eclipse was related to the [[solar cycle]].<ref>{{cite journal |title=Relation Entre l'Eclairement de la Lune Eclipsee et l'Activite Solaire |author-link=André-Louis Danjon |last=Danjon |first=A. |journal=L'Astronomie |year=1921 |volume=35 |pages=261–65 |bibcode=1921LAstr..35..261D}}</ref> An eclipse's rating on the scale is traditionally denoted by the letter ''L''.

==The scale==
The Danjon scale is described in the following table:

{| align=center class=wikitable
!L value
!Description
|-
|0
|Very dark eclipse. Moon almost invisible, especially at greatest eclipse.
|-
|1
|Dark eclipse, grey or brownish in coloration. Details distinguishable only with difficulty.
|-
|2
|Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.
|-
|3
|Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
|-
|4
|Very bright, copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.
|}

==Determining the value of L==

Determination of the value of L for an eclipse is best done near mid-totality with the naked eye.  The scale is subjective, and different observers may determine different values.  In addition, different parts of the Moon may have different L values, depending on their distance from the center of the Earth's [[umbra]].

==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 the 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 [[1991 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--indeed Danjon established the scale for this reason.

==References==
{{Reflist}}

==External links==
* https://web.archive.org/web/20050823095028/http://sunearth.gsfc.nasa.gov/eclipse/OH/Danjon.html

{{Lunar eclipses}}

[[Category:Lunar eclipses]]
[[Category:Scales]]