I remember my friend Kavin, who use to ask me repeatedly, "What is an Halo and how it is formed?". I had no answer to this question except that I knew it occurs quite regularly. So finally I decided to check on what an Halo is, and this is what I found.
Halos are nothing but a dim circle of light that is formed around the Sun or the Moon or any bright source of light for that matter (eg. a street lamp). These halos are formed due to ice crystals that are found in the clouds. These ice crystals acts as a lens reflecting and refracting the light.