Partial Lunar Halo

March 13, 2004


Provided and copyright by: Thomas Holmgren
Summary authors & editors: Jim Foster; Thomas Holmgren

The above photo showing a lunar halo was taken from Svalboviken, Sweden on February 5, 2004. Lunar halos and simple digital cameras aren't necessarily made for each other. Most digital cameras on the market don't allow shutter speeds long enough to capture the halo phenomenon, and if they do, you end up with a halo that barely fits in the picture. So, since I have a rather simple camera, this is a fortuitous shot of a portion of a 22 degree lunar halo.

The Moon was nearly full on this evening, and a lot of low altitude clouds passed above me, but once these clouds departed, a halo could be observed. Only the left half of the halo is visible on the photo (appearing to nip the tallest tree in the foreground). Halos can occur if hexagonal plate or column crystals in high altitude, cirrus-type clouds are more or less randomly oriented. Moonlight (in this case) enters one side of a crystal, is refracted, and then exits the opposite side, where it is again refracted by the same amount and in the same direction as the original refraction.

Camera: Fujifilm F5000, lens approx 37 mm, 2 sec exposure /f2.8.

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