Lunar Circumzenithal Arc

Circumzenithal arcs can be seen by moonlight as well as during the day. The lower light levels mean that the colour isn't usually visible to the eye which makes them hard to distinguish from wisps of cirrus.

While driving home I spotted a moondog and if sundogs are around it's always worth looking higher for the circumzenithal arc. When we found a safe place to pull over the moondog had gone but there was a streak of light in the right place to be a circumzenithal arc.

Propping the camera on the car roof I was able to get a long enough exposure to confirm the colour.

Reminder - always leave a tripod in the car!

When we got home another patch of cloud gave a strong arc which was bright enough to give a hint of colour.

This 4 second exposure clearly shows its true nature, and the stars of Leo shining through a gap below the arc confirm it is a night shot.

(Click on the image for a larger version)

For a few moments there seems to be a bit of supralateral arc branching off to the lower right of the arc, although this wasn't obvious at the time.

Canon EOS 5D   27th February 2013
Wiltshire, England

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