Jumping sundogs: A weird weather phenomenon

Discover how ice crystals create this rare halo around the sun

If you’ve ever seen what appear to be three bright Suns lined up neatly on the horizon, then you’ve probably witnessed sundogs. This rare phenomenon occurs when hexagonal ice crystals in the air align to refract sunlight into your eye at a precise angle. This forms a halo of light around the Sun, with two bright patches on either side of it called parhelia, or sundogs.

Even rarer are jumping sundogs, which occur when lightning discharge in a thundercloud temporarily changes the electric field above it. This adjusts the orientation of the ice crystals so that they refract the sunlight differently, making the sundogs move around as if they’re jumping.

As they need ice crystals to form, sundogs usually only appear during cold weather and when the Sun is low in the sky. However, they have been spotted from several different locations around the world. It’s not just the Sun either, as light from the Moon can generate Moon halos and moondogs in much the same way.

Sundog science

 This article was originally published in How It Works issue 77

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