- published: 05 May 2016
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A transit of Mercury across the Sun takes place when the planet Mercury comes between the Sun and the Earth, and Mercury is seen as a small black dot moving across the face of the Sun.
Transits of Mercury with respect to Earth are much more frequent than transits of Venus, with about 13 or 14 per century, in part because Mercury is closer to the Sun and orbits it more rapidly.
Transits of Mercury can happen in May or November. The last three transits occurred in 1999, 2003 and 2006 ; the next will occur in 2016.
Transits of Mercury can happen in May or November with May transits being about half as frequent as November transits. They currently occur within a few days either side of May 8 and November 10. November transits occur at intervals of 7, 13, or 33 years; May transits only occur at intervals of 13 or 33 years. May transits are less frequent than November transits because during a May transit, Mercury is near aphelion whereas during a November transit, it is near perihelion. Perihelion transits occur more frequently due to two effects: firstly, Mercury moves faster in its orbit at perihelion and can reach the transit node more quickly, and secondly at perihelion Mercury is closer to the Sun and so has less parallax.