When Venus passes directly between Earth and the Sun, it appears to observers as though a small disk is moving across the face of the Sun. Before the space age, such transits helped scientists calculate the distance between Earth and the Sun. Among the rarest of predictable astronomical phenomena, transits of Venus currently occur in a pattern that repeats every 243 years, with pairs of transits 8 years apart separated by gaps of 121.5 and 105.5 years. The first of a pair of transits of Venus in the beginning of the 21st century took place on June 8, 2004 (see Transit of Venus, 2004) and the next will be on June 6, 2012 (see Transit of Venus, 2012). After 2012, the next transits of Venus will be in December 2117 and December 2125.