Mercury completes rare 'transit'

Last lineup was 10 years ago, the next will be in 2019, followed by 2032 and 2049

Astronomers celebrated witnessing one of the highlights of the skywatchers' year on Monday, when the Sun, Mercury and Earth all lined up - a phenomenon that happens just a dozen or so times per century.

Mercury was seen through telescopes as a black dot inching over the face of our star, providing a celestial spectacle lasting seven and a half hours.