Ice Crystals

Because ice crystals can come in such a wide variety of shapes and sizes, the phenomena which they can produce are more varied than water drops. Also because the most common ice crystal phenomena, commonly called halos, are the 22 degree halo, and parhelia (also known as sun dogs), are seen in the direction of the sun, people are less likely to notice them by accident. When people do notice a strong 22 degree halo it can make a strong impression. It was seeing a very strong and complete 22 degree halo around the full moon which got me interested in atmospheric optics. At the time it seemed such a rare and beautiful sight. It is still beautiful, but not near as rare, as I now know when and where to look for halos. Once you get into the habit you will start noticing fragments of arcs in small isolated patches of wispy cloud.

Halos Displays of light formed in the sky by ice crystals in the atmosphere.

Sundogs or Parhelia Bright areas of light either side of the sun caused by ice crystals in the atmosphere.

Sun and Light Pillars Pillars of light above a low sun or artificial light.

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