Mercury will cross in front of the sun on May 9 in a rare event known as the Transit of Mercury. The Transit of Mercury will last up to seven-and-a-half hours and will be broadcasted live online from 7 a.m. to 2:45 p.m. EDT (9 p.m. to 4:45 a.m.) on the space broadcasting site Slooh.

Unfortunately, however, the Transit of Mercury will not be visible in Australia, New Zealand, and East Asia but can be seen in the Americas, the Atlantic and Pacific Oceans, Europe, Africa and the rest of Asia. The transit cannot be seen by the naked eye so a telescope with a solar filter is needed and if the weather permits, Mercury will look about 150 times smaller than the sun.

The Transit of Mercury occurs when the planet comes directly between the Earth and the sun during a rare event that only occurs 13 times every century in either May or November. The last transit happened in 2006.


Transit of Mercury. Mercury is the small dot in the lower center, in front of the Sun. The dark area on the left of the solar disk is a sunspot. Credit: Brocken Inaglory

Apparently, the transit comes in pairs and this year’s pair will occur on November 11, 2019. After that, viewers will have to wait until November 13, 2032.

On November 7, 1631, the first transit was observed by the French astronomer Pierre Gassendi. English astronomer Edmond Halley claimed that planetary transits are crucial to quantifying the distance of the Earth from the sun.

Nowadays, transits are used to seek exoplanets because the light from a star that an exoplanet orbits around drops as it crosses in front of it. Moreover, this can also determine the size of the exoplanet. Most planets cannot pass between the Earth and the sun due to their enormous size. Venus is the only planet besides Mercury to transit since it is closer to the sun than the Earth is.

The Transit of Mercury is not the only spectacular show to watch this month. Viewers can also catch a glimpse of the meteor shower called Eta Aquarids from May 5 to May 6.