Moondogs and Paraselenic Arc

March 24, 2022


MatthewC_moon-photo (003)

Photographer: Matthew Chin 
Summary Author: Matthew Chin; Jim Foster

The photo above show the evening sky and the Moon as viewed from Yuen Long, Hong Kong on December 17, 2021. Faintly colored arcs in the vicinity of the Moon are annotated. Though it’s not unusual to be able to see a 22-degree lunar halo, observing moondogs (on both sides of the Moon) and the paraselenic circle is much more challenging. The Moon must be bright, near the full phase, in order to detect these dim arcs. Note that the paraselenic arc passes through the center of the lunar disk and circles around the sky --- best seen with a fisheye lens. The bright streak at upper is a jet contrail.


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