Danjon scale

<h2 id="the-scale">The scale</h2>
<p>The Danjon scale is described in the following table:
</p>
<table><tbody><tr><th>L value</th><th>Description</th></tr><tr><td>0</td><td>Very dark eclipse. Moon almost invisible, especially at greatest eclipse.</td></tr><tr><td>1</td><td>Dark eclipse, grey or brownish in coloration. Details distinguishable only with difficulty.</td></tr><tr><td>2</td><td>Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.</td></tr><tr><td>3</td><td>Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.</td></tr><tr><td>4</td><td>Very bright, copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.</td></tr></tbody></table>
<h2 id="determining-the-value-of-l">Determining the value of L</h2>
<p>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 <a href="/facts/Umbra/JhPRXQ21">umbra</a>.
</p>
<h2 id="factors-affecting-the-value-of-l">Factors affecting the value of L</h2>
<p>Many factors can affect the appearance of the Moon during a lunar eclipse.  The Moon's path through the Earth's <a href="/facts/Umbra/JhPRXQ21">umbra</a> is important, but so too are the current conditions of the <a href="/facts/Earth%27s_atmosphere/FV97Am25">Earth's atmosphere</a>.  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.
</p><p>The amount of light refracted affects the brightness of the moon at mid-eclipse, and this depends on several factors.  <a href="/facts/Volcanic/c2M5upml">Volcanic</a> eruptions are one of the most significant - eruptions which spew significant amounts of <a href="/facts/Volcanic_ash/c3cqgBfV">volcanic ash</a> into the air are generally followed by several years of dark, deep red eclipses.  The effect of the <a href="/facts/1991_eruption_of_Mount_Pinatubo/8yhb1Y9n">1991 eruption of Mount Pinatubo</a> on subsequent lunar eclipses was very noticeable, with the eclipse of 9 December 1992 rated 0 on the Danjon Scale by many observers.
</p><p>It is also thought that the <a href="/facts/Solar_cycle/QrP4Egea">solar cycle</a> has some effect on the darkness of lunar eclipses--indeed Danjon established the scale for this reason.
</p>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://web.archive.org/web/20050823095028/http://sunearth.gsfc.nasa.gov/eclipse/OH/Danjon.html">https://web.archive.org/web/20050823095028/http://sunearth.gsfc.nasa.gov/eclipse/OH/Danjon.html</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Danjon, A. (1921). "Relation Entre l'Eclairement de la Lune Eclipsee et l'Activite Solaire". L'Astronomie. 35: 261–65. Bibcode:1921LAstr..35..261D. <a href="/wiki/Andr%C3%A9-Louis_Danjon" target="_blank">/wiki/Andr%C3%A9-Louis_Danjon</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
</ol>

Danjon scale open-in-new

Danjon scale