Monday, January 4, 2010

Another ring around the moon - this time, on a cold, clear night

A circular ice halo formed around a waning moon in the clear of Sunday morning.

Florida's Space Coast this week is experiencing one of its deepest cold snaps of the past decade. For about five consecutive days, the temperature has been and still is forecast to be around freezing. Some sheltered inland areas of Brevard County could dip into the upper 20s. On Sunday, the high temperature of 52 in Melbourne was its lowest ever recorded on the same date.

That caused this native Mainer to break down and turn on the heat for the first time this winter. And I think I remember using the air conditioner just last week.

If it's near freezing on the ground, it's even colder up there in the lower atmosphere, which tends to create many of the scenes for my photos. Sunday morning's phenomenon was the same as Saturday morning's, but it came under different conditions. The sky for Sunday's halo was completely clear, allowing for a more defined ring, whereas we were on the verge of a rainstorm Saturday morning.

These circular halos are caused by ice crystals suspended in the upper troposphere. Those wispy cirrus clouds we see mostly just in the winter here in Florida contain lots of ice and supercool water. When the moonlight refracts through them, a halo appears. It's sometimes possible to make out the colors you'd typically see in a rainbow, which is why some halos are called icebows.

Earth's a cool planet, isn't it?

So much so that I need a hot chocolate.

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