2006-03-19 06:32:55.000 – Ryan Knapp,  Observer

Corona around the moon…

For the past two nights, the fog at the summit has been either thin or nonexistent. As the newest observer at the summit, I find that the fog at the summit the most difficult element to predict. During the previous weeks shift, I predicted the summit was going to be clear under partly cloudy skies. When I went to sleep at 0530 EST, the summit was just that, in the clear under mostly clear skies. When I woke up at 1400 EST, the summit was in the fog. The same thing has been happening the past two nights. All indications point to the summit being mostly in the fog but slowly the cloud layer providing us with the fog slowly starts to drop below the summit.

But I am not entirely upset that the summit has been poking its head above the summit because it sets up some interesting and beautiful sites. Aside from the undercast skies, picturesque sunrises, and rime ice not forming as quickly, there has been a corona around the moon. Coronas are a set of one or more colored rings closely surrounding the moon (or sun in the day). The closer rings to the light source are a bluish white and the rings on the outside have a reddish ting, the opposite of a halo. Coronas are commonly formed by water droplets from high clouds, fog, or mist. The more uniform the particle radii’s are the more discernible and colorful the rings appear to be. When the droplets have a broad range of droplet sizes, the rings will be distinctly discernable but the colors will start to wash out. This is commonly called an aureole. Ice crystals can form a corona as well with discernable rings but the colors wash out and it appears almost white. The coronas that I have been witnessing have been a variation of all three. One observation I might go out and the corona is being formed by high clouds. The next observation it is being created by freezing fog. The next observation it’s being created by high level blowing snow. Regardless of how it is being formed, it is a colorful sight and something to look forward to seeing at each observation time.


Ryan Knapp,  Observer

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