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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 faster.

Transits of Mercury can happen in May or November. November transits occur at intervals of 7, 13, or 33 years; May transits only occur at intervals of 13 or 33 years. The last two transits were in 1999 and 2003; the next two will occur in 2006 and 2016.

During a May transit, Mercury is near aphelion and has an angular diameter of 12"; during a November transit, it is near perihelion and has an angular diameter of 10".

The first observation of a transit of Mercury was on November 7 1631 by Pierre GassendiPierre Gassendi ( January 22, 1592 October 24, 1655) was a French philosopher, scientist and mathematician. He is best known for attempting to reconcile Epicurean Atomism with Christianity. He was born of poor parents at Champtercier, near Digne, in Prove. He unsuccessfully attempted to observe the transit of Venus just one month later, but due to inaccurate astronomical tables he did not realize that it was not visible from most of Europe, including Paris. A transit of Venus was not observed until 1639Events January 14 Connecticut's first constitution, the " Fundamental Orders," is adopted. March 13 Harvard University is named for a clergyman named John Harvard. November 24 Jeremiah Horrocks observes the transit of Venus. Charles I starts the first of, by Jeremiah HorrocksJeremiah Horrocks (c. 1618 January 3, 1641), sometimes given as Jeremiah Horrox was an English astronomer who made the first observation of a transit of Venus. Horrocks was born in Toxteth Park, near Liverpool in Lancashire. His father was a small farmer,.