The Sun turned purple in California last week. The fantastic sight came from the smoke of hundreds of wildfires that broke out in tinder-dry conditions across the state. The tiny bits of soot that filled the air were just the right size to scatter the red colours of sunlight and let through shades of purple.

Scotland witnessed its own surreal spectacle on September 26, 1950, when the Sun turned blue. “All over the city people stopped to gaze at the sapphire sphere,” described The Scotsman in Edinburgh. The newspaper’s switchboard was jammed with callers, some of whom thought the end of the world was coming. And later that night the country was treated to the sight of a blue Moon.

An RAF jet fighter was sent up to investigate and reported that the Sun was a vivid blue up to a few miles high, where a layer of smoky brown haze was hanging. Above that the Sun looked normal. The smoke had come from massive wildfires in Alberta that turned the Sun purple or orange across much of North America. The smoke was then blown across the Atlantic.

Wildfires are not that unusual, so why is the proverbial Blue Moon, or Blue Sun, not seen more often? The smoke particles from the fires have to be the same specific size and that is quite rare.