Tuesday, November 8, 2011

ring around the moon

ring around the moon
peeking through a mackerel sky -- 
rain is on the way

On a clear evening, a gibbous moon with a pink halo winks on and off as a fleet of cottonball clouds pass by. There's an old saying: "Ring around the moon means rain soon." And sure enough, the next day a long, hard rain fell for the first time in many moons.
          A dappled patch of tiny individual cloudlets at high altitude is called cirrocumulus. Sometime the little cloudlets look like fluffy fish scales, giving the appearance of a "mackerel sky." Cirrocumulus usually move from west to east and indicate unsettled weather on the way. These high clouds contain millions of tiny ice crystals and the halo around the moon is caused by light glinting from the ice crystals. 
          Like a rainbow, a lunar halo depends on the viewer's perspective. The halo you see will not be the same as the one for the person standing next to you because the particular group of ice crystals is different for each person. Since moonlight is not very bright, lunar halos are mostly colorless, though some, like this one, are reddish on the inside and bluish on the outside. Without the cloud cover, the inner edge of the halo would appear sharp and the outer edge diffuse. 
          My personal halo looks like a pink pearl inside an oyster shell. What does it look like to you?

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