predict lunar eclipses.
The moon appears to phase in and out of darkness to an Earth bound observer on a monthly cycle, but in reality the Sun's rays are always falling upon the moon. The arced and crescent moon shapes are due to our perspective on Earth of the spherical moon being illuminated from a single direction. The rotation of the moon and the revolution of the moon are synchronously locked in a period of 27 days, 7 hours, and 43 minutes such that only one lunar hemisphere is ever visible from Earth and the other side is apparently locked in darkness. In reality the dark side of the moon sees just as much Sun as the near side on a lunar day cycle almost matching the revolution period. Despite the moon's serene appearance it is a place of extremes because without an atmosphere the Sun heats the moon to 250 Fahrenheit (123 Celsius) during its day and the moon cools to -390 Fahrenheit (-233 Celsius) during its night.
There is of course one time in which the Sun's rays are not falling upon the moon. During a total lunar eclipse the Earth blocks the light from the Sun and the Earth's shadow casts the moon into a dark red copper shadow. A total lunar eclipse will be viewable tonight in the Northern Hemisphere at U.T. 7:41 (or E.S.T. 2:41 am or P.S.T. 11:41 pm). NASA has some further information about the lunar eclipse here. Unfortunately, clouds may block your view so check the weather, indeed here in Seattle the weather may completely block this rare winter solstice lunar eclipse. That is right, this lunar eclipse occurs on the winter solstice. This really is a rare event!
As solace I have looked up several times recently in Seattle to see a moon dog or a moon ring. A moon dog and moon ring is a halo (the ring) and bright spots (the dog) to the left and right of the moon created by the moon's light refracting through ice crystals or high clouds in the atmosphere. Even if you can't see the Eclipse tonight look up this winter to perhaps see the Moon's winter halo.
No April fools around here
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