Full Moon Clouds

Particles in the atmosphere can obscure clear views of the Moon from Earth, producing interesting optical effects. It is probably more noticeable during a full moon, but it can happen at any phase in the lunar cycle.

The first type is a Moon Ring, which is a circle that encompasses the entire moon. This forms when moonlight is refracted by ice crystals in the atmosphere. All ice crystals are approximately the same size, so the ring does not differ much in shape. Moon Rings are rumored to signify that bad weather is ahead. This superstition has some basis in reality though since the ice crystals signify high altitude cirrus clouds, which in turn predict a warm pressure system coming in one or two days. And a warm pressure system means a storm.

Moon Dogs are also caused by interference in the upper atmosphere, this time producing bursts of red and blue light on both sides of the Moon. Clouds in the atmosphere at an altitude of about 30,000 feet are full of ice crystals, which refract the moonlight again and cause a bright spot in the Moon Ring. These are not as common phenomenon because it requires an extremely bright and therefore Full moon to produce the spots. The color is not as easily distinguishable in Moon Dogs as it is in the analogous Sun Dogs because the light at night is not bright enough to activate the cone cells in human eyes.

A Moon Corona is similar to Moon Rings, but they are much smaller in size. They are caused by high, thin clouds in the atmosphere. The corona is typically only a couple of degrees in diameter, closely covering the moon. Once again, colors are produced, but it is harder for the human eye to detect color at night.

Moon Pillars, in contrast, are formed by reflecting light off of ice crystals. Refracted light produces colored light rays, but reflected light retains the color of the light source. When the moon is near the horizon, either rising or setting, a shaft of white light appears above and below the moon.

The nighttime counterpart to Rainbows are Moon Bows. There is less light coming from the Moon than directly from the Sun, so Moon Bows only have a hint of color and are less defined. They form in the same way though, from light hitting rain drops that act as prisms.

If the Earth had no atmosphere, the moon and stars would appear crisp and clear at all times. On good viewing nights, the atmosphere has little to block a clear sight of the sky. On other nights, ice crystals or clouds reflect moonlight and cause strange formations of light. Clouds in the upper atmosphere, which may or may not even be visible from the perspective of Earth, are a common reason for these strange bursts of moonlight.




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