When the Sun shines through a thin layer of cloud, it can create an optical effect known as a corona. This appears as a bright disc of light centred on the Sun, often surrounded by rings of iridescent colours. The effect is caused by the cloud’s tiny water droplets (or, more occasionally, ice crystals) bending, or diffracting, the sunlight passing around them. And the size of the cloud particles determines the size of the corona rings. That is why this corona is not quite circular.

Smaller droplets (or ice crystals) form larger rings and vice versa. The size of the cloud droplets likely varied across this thin Altostratus spotted by Tim, son of Gillian Smith (Member 41,732), over Col Sud de Menouve, Italy. As a result, the corona they produced was distorted and off centre – a multicoloured blaze in the sky that looped lopsidedly around the dazzling disc of the Sun.