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NEWSCIENCE If you know where and when to look, you can treat yourself to a colourful display of atmospheric haloes, spots and pillars. These images can tell you something about the clouds overhead and possible changes in the weather. All of these images are cre ....

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.... each crystal, the light changes direction, or refracts. The radius of the hale depends on the amount of change in the direction of the sun's light. Usually this is 22 degrees. Since the sun is 1/2 of a degree across, the radius of the halo is 44 sun-widths. Occasionally you may see a second halo at 46 degrees from the sun (that is, with a radius of 92 sun-widths). This is produced by sunlight passing through both the side and bottom of each crystal. Moonlight will also produce a halo, around the moon, with the proper layer of cirrostatus. Another common optical effect is known as "mock suns" or "sun dogs" or "parhelia" (Greek for "with the ....