Why does the moon look red during a lunar eclipse?
In a total lunar eclipse the sun, earth and moon line up and the Earth casts its shadow on the moon.
The moon is always a full moon during a total lunar eclipse and it never goes completely dark. It appears reddish for the same reason that sunsets and sunrises often have a red tint.
The Earth’s shadow has two parts: the umbra and the penumbra. A small amount of the sun’s energy directly shines within the penumbra.
None of the sun’s rays shine directly in the umbra part of the shadow, so it is the darkest part of the shadow. A total lunar eclipse occurs when the moon travels through Earth’s umbra.
The umbra is not pitch black because of the Earth’s atmosphere. Sunlight is scattered, or redirected, in all directions by the Earth’s atmosphere into the penumbra and umbra.
As light passes through the atmosphere, the blue colors are scattered out of the path. Red and orange light passes through the atmosphere and is scattered into the shadow zone. If our planet had no atmosphere, then the moon would be completely dark during a total lunar eclipse.
A total lunar eclipse will occur Monday-Tuesday across the United States and Canada. If it is cloudy or you miss seeing this total lunar eclipse, three more total lunar eclipses will be viewable from our area on Oct. 8 of this year, and next year on April 4 and Sept. 29.
The last total lunar eclipse viewable from our area was in December 2011, so this many over the next year is a bit unusual.