Editing Lunar eclipse (section)

== Lunar versus solar eclipse ==
[[File:Lunar eclipse oct 8 2014 Minneapolis 4 46am.png|thumb|320px|In a lunar eclipse, the Moon often passes through two regions of [[Earth's shadow]]: an outer penumbra, where direct sunlight is dimmed, and an inner umbra, where indirect and much dimmer sunlight [[atmospheric refraction|refracted]] by Earth's atmosphere shines on the Moon, leaving a reddish color. This can be seen in different exposures of a partial lunar eclipse, for example here with exposures of 1/80, 2/5, and 2 seconds.]]

There is often confusion between a solar eclipse and a lunar eclipse. While both involve interactions between the Sun, Earth, and the Moon, they are very different in their interactions.

The Moon does not completely darken as it passes through the umbra because of the [[atmospheric refraction|refraction]] of [[sunlight]] by [[Earth's atmosphere]] into the shadow cone; if Earth had no atmosphere, the Moon would be completely dark during the eclipse.<ref>{{Cite web |url=http://eclipse.gsfc.nasa.gov/LEcat5/appearance.html |title=Visual Appearance of Lunar Eclipses |last1=Espenak |first1=Fred |last2=Meeus |first2=Jean |publisher=NASA |quote=The troposphere and stratosphere act together as a ring-shaped lens that refracts heavily reddened sunlight into Earth's umbral shadow.}}</ref> The reddish coloration arises because sunlight reaching the Moon must pass through a long and dense layer of Earth's atmosphere, where it is [[Rayleigh scattering|scattered]]. Shorter [[wavelength]]s are more likely to be scattered by the air molecules and [[particulates|small particles]]; thus, the longer wavelengths predominate by the time the light rays have penetrated the atmosphere. Human vision perceives this resulting light as [[red]]. This is the same effect that causes [[sunset]]s and [[sunrise]]s to turn the sky a reddish color. An alternative way of conceiving this scenario is to realize that, as viewed from the Moon, the Sun would appear to be setting (or rising) behind Earth.

The amount of refracted light depends on the amount of [[particulates|dust]] or [[cloud]]s in the atmosphere; this also controls how much light is scattered. In general, the dustier the atmosphere, the more that other wavelengths of light will be removed (compared to red light), leaving the resulting light a deeper red color. This causes the resulting coppery-red hue of the Moon to vary from one eclipse to the next. Volcanoes are notable for expelling large quantities of dust into the atmosphere, and a large eruption shortly before an eclipse can have a large effect on the resulting color.

[[File:Eclipse Christophe Colomb.jpg|thumb|[[Christopher Columbus]] predicting [[March 1504 lunar eclipse|a lunar eclipse]]]]