Why do we see halo around the moon sometimes?

Why do we see halo around the moon sometimes?

PROF WAQAR HUSSAIN

               Ans:- Halo is a circle of white coloured light round the moon. It does not appear on every night but can be seen occasionally. The halo round the moon on a clear night is due to the refraction of light by small ice-crystals in the air. Many unexplained myths are related to the halos that have no scientific explanation.