A large halo around the sun was seen from various locations in Singapore yesterday afternoon.
Photos of it posted online were taken in places such as Changi, Marina Bay and Toa Payoh.
The optical phenomenon, which is not uncommon, typically occurs when there are thin clouds so high in the sky that they are made of ice crystals rather than water droplets.
The crystals act as tiny prisms, reflecting and refracting light in such a way that a ring is seen around the sun. Such a halo is referred to as a sun halo, solar halo or 22-degree halo, where 22 degrees is the angle formed between one's eye and the edge and centre of the halo.
A reader once asked if it was possible to forecast when something like this would happen.
The National Environment Agency said it was difficult to forecast the precise location of these ice crystals in the atmosphere, which would determine where the halo could be sighted. It also said that while it was safe to look at the halo itself with the naked eye, it was dangerous to look at the sun directly without proper protection.