Go Tripping: The Worlds Wildest Optical Illusions

St Elmo's fire, Edinburgh, Scotland

Caesar saw it on the javelins of his troops the night before battle; Herman Melville called it 'God's burning finger'. Caused by the discharge of electricity from storm clouds to the earth, this stunning consequence has forever conjured beliefs of omens and godly intrusion. It's frequently seen on the flagpoles of ships during a storm; sailors would hail the sight, as it usually comes at the point where a storm is quietening down. St Elmo was a guardian of sailors, and it was seen as his calling card. The effect is recurrently glimpsed on the loftiness of Edinburgh's Castle Rock.