Fire Rainbow - A fire rainbow is an extremely rare phenomenon that occurs only when the sun is high allowing its light to pass through high-altitude cirrus clouds with a high content of ice crystals.
Green Ray - Also known as the Green Flash. This occurs very briefly before total sunset and after sunrise. It appears as a green flash above the sun that lasts very briefly, generally only a few moments. It is caused by refraction of light in the atmosphere.
Haloes - Like rainbows, haloes are formed around the Sun due to moisture (in this case ice crystals) being refracted from the Sunâ€™s rays in the upper atmosphere. Sometimes two or more areas of the circle or arcs surrounding the Sun will be brighter, forming what are called Sun Dogs. Haloes can also form around the Moon, and occasionally around the brighter stars and planets like Venus.
Mammatus Clouds - These odd-shaped clouds are often associated with a storm front, especially one involving a thunderstorm. It's not completely understood how they form.
Mirages - Mirages occur when light is refracted to produce an image of an object or the sky where it is not. It is most commonly seen on hot surfaces, such as the pavement or a desert.
Pyrocumulus Clouds - Another heat related phenomenon, pyrocumulus clouds form from the fast and intense heating of an area to create convecture, which in turn creates a cumulous cloud. Volcanoes, forest fires, and nuclear explosion (in the form of a mushroom cloud) are all prime causes of pyrocumulus clouds.
Moon Bows - A rainbow is caused by the Sun shining on moisture droplets, most commonly in a post-rain atmosphere. A moon bow is much rarer, only seen at night when the moon is low and full to almost full. One popular place to see moon bows is at Cumberland Falls in Kentucky.