In every century there are only 13 or 14 transits of Mercury and you have to be on the right part of the globe if you want to watch a particular transit from beginning to end, which usually lasts for several hours.
The solar system’s smallest and most remarkable planet, Mercury, will cross the face of the sun on May 9 – offering a great opportunity for people in many places across the world to see it.
Mercury is a dark and enigmatic world, which bears the scars of a strangely long history of volcanic eruptions and tectonic activity. Its crust is unreasonably rich in elements that normally easily evaporate from the surface, such as sulphur, sodium and potassium. This is odd, as these are the kind of substances that are most likely to have been lost during a hot and violent birth such as Mercury’s.
Mercury scoots round the sun in only 88 days, overtaking the more sedately moving Earth every three or four months. Because Mercury’s orbit is tilted at about seven degrees with respect to the Earth’s, it passes directly between us and the sun (a transit) only when both it and the Earth are close to the points where their orbital planes intersect. This can happen only in early May or early November.