On its science site, NASA documents (opens in new tab) a rare incidence of a quadruple lunar halo. This causes light to be dispersed at a wider angle - one greater than the angle of minimum deviation - creating a halo with a more blurry and diffuse outer edge. Larger and much fainter than 22-degree halos, 46-degree halos form when sunlight enters randomly oriented hexagonal ice crystal at its face and exits through its base. Halos with a radius of 22 degrees can also be accompanied by 46-degree radius halos, which can also occur independently too. (Image credit: karinegenest via Getty Images) (opens in new tab) Moon halos are closely related to 'sun dogs', a solar phenomenon where pillars of light appear on either side of the sun. Not only are lunar halos closely related to solar halos, but this icy refractive effect can also create rings opposite these astronomical bodies, or pillars of light, and even 'sun dogs' - concentrated patches of sunlight seen 22 degrees to the left or right of the sun that can appear in pairs.

On rare occasions, these double halos even possess spokes radiating out to their outer edges. In addition to this, refraction from ice crystals can also create double halos. Lunar halos aren't connected to coronas, which are around half as wide as halos with a radius of around 10 degrees, as these optical effects are caused by water droplets rather than ice crystals. Lunar halos are often accompanied by smaller more colorful rings that are caused by refraction and reflection of light by water molecules in the atmosphere called coronas. This means that the sky inside a 22-degree halo can often appear darker than the surrounding sky making it appear like a 'hole in the sky.' Do lunar halos have company? The optical properties of the ice crystals also mean that they don't direct light back toward the center of a halo. Related: What are sundogs and how do they form? Colors in the lunar halo are often too weak to be seen with the naked eye and may be much more visible around the sun because of how much brighter it is than the moon.

This means that lunar halos can be very lightly tinted with rainbow colors, longwave red light on the inside, and shortwave blue light on the outside. This happens because different wavelengths of light, thus different colors, experience a different degree of refraction when they pass through a prism. (Image credit: ClickAndPray Photography via Getty Images) (opens in new tab) The radius of a moon halo is roughly the length of an outstretched hand at arm's length.

Optical glow red giant