BRITAIN-SCIENCE-ASTRONOMY-MERCURY

Sumitra Sri Bhashyam from Flamsteed Astronomy Society looks through protective glasses at Mercury moving across the face of the sun at the Royal Observatory in Greenwich on May 9, 2016. Astronomers today were preparing for one of the highlights of the skywatchers' year, when the Sun, Mercury and Earth all line up -- a phenomenon that happens just a dozen or so times per century. Mercury will be seen through telescopes as a black dot inching over the face of our star, providing a celestial spectacle that will last seven and a half hours. / AFP / LEON NEAL (Photo credit should read LEON NEAL/AFP via Getty Images)