Hyderabad, June 2 : People in Hyderabad and surrounding districts on Wednesday witnessed a rare spectacle in the sky. A circular halo around Sun dazzled the citizens in several parts of Hyderabad and in neighbouring Medak, Siddipet and Sangareddy districts. People stepped out to see the rainbow-coloured ring around the Sun, also called '22 degree halo'. This was visible between 11 a.m. and 12.30 noon. Surprised to see the rare phenomenon, several citizens captured the image on their mobile phones and shared it on various social media platforms. Sun halo is an optical phenomenon that occurs due to sunlight refracting in millions of hexagonal ice crystals in the cirrus cloud. It takes the form of a ring with a radius of approximately 22 degrees around the sun or the moon. According to the UK-based Atmospheric Optics, a knowledge-sharing website, 22 degree halos are visible all over the world and throughout the year. Halos are formed whenever the sky is wisped or hazed with thin cirrus clouds. These clouds are cold and contain ice crystals in even the hottest climes. A few hours after sun halo, parts of Hyderabad and surrounding districts received rains. /IANS