When a ring appears in the sky around the sun, it is called a halo. Halos have also been observed around the moon in the night sky.
A halo appears around the sun when thin cirrus clouds containing tiny ice crystals occur above about 20,000 feet. The sunlight is refracted by the ice crystals and produces a ring that appears 22 degrees from the sun. Most halos are bright white, but the dispersion of the light is also capable of causing a halo to have colors, sometimes with a red band toward the inside and a blue band toward the outside. Lunar halos are more likely to be white since moonlight is not as bright as sunlight. Halos appear most frequently in the winter, spring and autumn.