The Shape of Night

“Blood Moon”
Painting by Keith Pearman.

Tomorrow night (September 27-28) we will have a total lunar eclipse beginning around 9:07 and lasting until 12: 27.  This event will be safe to watch without any special equipment.

This eclipse is the final in a series of 4 total lunar eclipses half-year apart.

Our minister at the Unitarian Universalist Church of Greensboro has asked me to say a few words tomorrow during the worship service.  She wants me to describe the eclipse scientifically in 3 to 5 minutes.

The moon is about a quarter of a million miles away, and it takes the moon a little more than 29 ½ days to orbit the Earth one time.  One might think we should have a lunar eclipse every month, at every New Moon,  But our moon’s orbit is slightly tilted relative to Earth’s orbit around the Sun, (5 degrees) so most times the Full Moon slides above or below the Earth’s shadow; or partly thru the Earth’s shadow giving a penumbral or partial eclipse. Earth’s umbra, the darkest part of the shadow is about 5,500 miles wide (2.6 moon diameters.)

Every so often the moon will travel thru the umbra, the dark part of shadow of the Earth and we will experience a lunar eclipse. On average, we get 3 total lunar eclipses every two years. For any particular place on Earth, a total lunar eclipse will occur about every 2 ½ years. The next total lunar eclipse will be in 2018 visible from Australia. Our next total lunar eclipse in North Carolina: January 2019.

Lunar eclipses can only happen when the moon is full.  And since the earth has an atmosphere (about 50 miles thick) some sunlight gets thru and shines on the moon during an eclipse. The light from all the sunrises and sunsets all around the earth travels thru the atmosphere and refracts, gets bent.   The colors green, blue, indigo and violet mostly get filtered out. The reddish portion of the spectrum is least effected and it comes thru Earth’s atmosphere and shines on the eclipsed moon. Depending on what type of dust particles and how many clouds are in Earth’s atmosphere at the time of the eclipse, the moon could be yellow, orange or brown as well as red during totality.

So enjoy the eclipse (if the clouds cooperate,)  Come back here and describe the color you see at totality.   

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