text: what does it mean when there is a ring of clouds around the moon? last night that was what was with the moon. i was just wondering if there was anything about the moon when it does that. explanation: have you ever seen a halo around the moon? this fairly common sight occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. each ice crystal acts like a miniature lens. because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the moon halo. a similar sun halo may be visible during the day. the town in the foreground of the above picture is san sebastian, spain. the distant planet jupiter appears by chance on the halo's upper right. exactly how ice-crystals form in clouds remains under investigation.   the moon can produce interesting optical effects when conditions are right. the most common of which are moon rings, moon bows, which are similar to rainbows, moon dogs and moon pillars. a rainbow is produced when sunlight is refracted through water droplets - a similar effect is produced when moon light refracts through ice crystals. below are a few photographs and examples about this interesting phenomena. thanks to everyone that helped me put together this simple explanation of moon light effects.     a ring around the moon the ring around the moon is caused by the refraction of moonlight (which of course is reflected sunlight) from ice crystals in the upper atmosphere. the shape of the ice crystals results in a focusing of the light into a ring. since the ice crystals typically have the same shape, namely a hexagonal shape, the moon ring is almost always the same size.   less typical are the halos that may be produced by different angles in the crystals. they can create halos with an angle of 46 degrees.    moon ring weather folklore  folklore has it that a ring around the moon signifies bad weather is coming, and in many cases this may be true. so how can rings around the moon be a predictor of weather to come? the ice crystals that cover the halo signify high altitude, thin cirrus clouds that normally precede a warm front by one or two days. typically, a warm front will be associated with a low pressure system which is commonly referred to as a storm.  it is believed that the number of stars within a moon halo indicate the number days before bad weather will arrive. give it a try the next time you observe a moon halo.   rings around the sun - the same phenomena that causes lunar halos can also be observed around the sun. a few photos of solar halos using a coolpix 995 digital camera.   notice: never look at or photograph the sun directly.     --------------------------------------------------------------------------------   anatomy of a moon halo the ring that appears around the moon arises from light passing through six-sided ice crystals high in the atmosphere. these ice crystals refract, or bend, light in the same manner that a camera lens bends light. the ring has a diameter of 22° , and sometimes, if you are lucky, it is also possible to detect a second ring, 44° diameter. thin high cirrus clouds lofting at 20,000 feet or more contain tiny ice crystals that originate from the freezing of super cooled water droplets. these crystals behave like jewels refracting and reflecting in different directions.   cloud crystals are varieties of hexagonal prisms, (6 sides) and range in shapes from long columns to thin plate-like shapes that have different face sizes.     -------------------------------------------------------------------------------- moon dogs moon dogs are the paler version of sun dogs: bursts of light often in reds and blues that appear on both sides of the moon. both phenomena are the work of almost invisible clouds that reside in the atmosphere where commercial airliners cruise, at about 30,000 feet. the clouds are composed largely of ice crystals, known as diamond dust. the official name for a moon dog is a paraselene if seen at 22 degrees. if the image is at 90, 120 or 140 degrees then it'