Friday, January 1, 2010

Christmas Halo and a Blue Moon

The last week of December gave us great weather for sky viewing.  We had several clear and cold nights that led to the formation of frost-ice crystals in the sky. This made conditions perfect for seeing several optical formations in association with the moon, as the tiny ice crystals in the atmosphere created halos by refracting and reflecting light.

Solar activity has remained low and so far this winter there have been very few good aurora borealis viewing days in our area. However, just before Christmas there was a burst of solar energy from the sun and we were treated to a nice display early Christmas Day.  Besides the aurora we were treated to a halo and moon dogs as the moon was setting low in the western sky.  I was able to get a picture of both the moon halo and aurora together. As mentioned above, the tiny ice crystals in the atmosphere create halos by refracting and reflecting light.


Aurora Borealis mixed in with a halo and moon dogs.

As the moon became full, conditions on the last two days of December were ideal for several types of optical phenomena involving the moon. One involved what is referred to as a Blue Moon, which is a second full moon in a single month. On the evening of the 30th, I also filmed a complex halo display.  There was a 22 degree halo around the moon with a parhelic circle running parallel to the halo, and where they intersected, moon dogs or parselena appeared. The 22 degree halo is  formed when moonlight passes through pencil-shaped ice crystals floating in freezing clouds. When parhelia and moon dogs are present you know that there is a mixture of plate-shaped ice crystals that are reflecting light to create these, and the pencil-shaped ones that form the halo. For more on ice crystals see:

BlueMoonHalo_2009 Complex halo with moon dogs and parhelic circle. Bright star upper center is Mars.


Moon with Halo over our home.

Not pictured in the first photo was a fleeting but bright circumzenithal arc above the halo.  It wasn’t attached to the halo and was right overhead.  They are formed by the same crystal formation as the parhelia’s plate-shaped ones. Circumzenithal arcs are some of the brightest of the ice crystal phenomena due to the refraction through the ice crystals.  They can rival a rainbow in color, but unlike a rainbow they are seen on the same side as the sun or moon.  It resembles an upside down rainbow but the red is on the outside.


Circumzenithal Arc is the most beautiful of all the halos.

In the early hours of December 31, I took a picture of our homestead in the bright moon light and a small patch of cloud iridescence can be seen in the thin cloud next to the moon.


Moon light showing some iridescence in the clouds.

The last optical phenomena seen during this time was a diffraction coronae around the full blue moon on New Year’s eve.  The moon was shinning through a thin layer of cloud and a series of concentric colored rings formed around it.  You have the colorless center aureole, then a bluish and reddish ring.


Coronae around the moon sitting over Drilling Rig.


Moon with coronae framed by caribou antlers.

All in all it was a great way to end 2009.  Here is best wishes to all for the coming New Year and keep looking up.


2009 Blue Moon over Colville Alaska.

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Arctic Smoke Signals by James W. Helmericks is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.