Transit of Mercury

During a transit, Mercury appears as a tiny black dot moving across the Sun as the planet obscures a small portion of the solar disk.

[1] The orbit of the planet Mercury lies interior to that of the Earth, and thus it can come into an inferior conjunction with the Sun.

Depending on the chord of the transit and the position of the planet Mercury in its orbit, the maximum length of this event is 7h 50m.

Using continued fraction approximations of the ratio of these values, it can be shown that Mercury will make an almost integral number of revolutions about the Sun over intervals of 6, 7, 13, 33, 46, and 217 years.

In 1894 Crommelin[15] noted that at these intervals, the successive paths of Mercury relative to the Sun are consistently displaced northwards or southwards.

For both the May and November series, the path of Mercury across the Sun passes further north than for the previous transit.

[18] At inferior conjunction, the planet Mercury subtends an angle of 12″, which, during a transit, is too small to be seen without a telescope.

[19] A common observation made at a transit[20] is recording the times when the disk of Mercury appears to be in contact with the limb of the Sun.

Johannes Kepler had predicted the occurrence of transits of Mercury and Venus in his ephemerides published in 1630.

The Shuckburgh telescope of the Royal Observatory, Greenwich in London was used for the 1832 Mercury transit.