If a circle around the sun or moon, rain will come soon

These circles, called halos, appear when there is ice crystals, which form cirrus clouds, high up in the atmosphere. The cirrus clouds show there is moisture in the atmosphere. The ice crystals reflect and refract the light, like tiny prisms. Halos are a good indication that there is an approaching frontal system, but they are not always followed by rain or snow.

Source: EPA