A Moon Halo is technically known as a 22-degree halo, as the light creates a radius of exactly 22 degrees around the Sun or Moon. This will depend on the one you’re seeing at the time when the halo is around them. The Moon Halo forms when moonlight is refracted by millions of hexagonal ice crystals that are suspended in the atmosphere. Usually, most measure the radius for this by the length of an outstretched hand at arm’s length. Due to ice crystals being involved, most assume you will only see these halos during cold times of the year or in cooler climates. Yet they can happen anywhere, especially because nighttime temperatures are often cooler anyway.