Lunar Halo

Those who attended the Romance on the Mountain dinner at the Boarding House last Saturday were treated to a wonderful dinner and a wonderful celestial event afterward. Looking up as we were walking out (yes much wine was consumed but our eyes were still sharp) we saw the most prominent lunar halo I have ever seen. A not uncommon phenomenon, a lunar halo or ring is caused by ice crystals in the upper atmosphere. It apparently takes a combination of a nearly full moon (it was two days past first quarter) and a cold, clear night with high altitude moisture. Because water ice bends light at an angle of 22 degrees, lunar halos are 44 degrees wide (for reference the moon is only 0.5 degrees in diameter). Similar effects are seen with the sun under the right daytime conditions. By the time I made it home through the Balsam mud and snow it was just about gone. The links below contain some good photos (you have to be in the right place at the right time with your camera ready) and further details on the phenomenon.


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