The rare space event, known as Mercury in Transit, will see the planet at the front of the solar system travel across the face of the sun as seen from Earth. Mercury in transit only happens on average 13 times a century, despite only taking 88 days to complete an orbit of the Sun. The reason we rarely see the transit is due to the smallest planet in the solar system’s slightly wonky orbit.
The planet’s orbit has an incline of seven degrees, in relation to Earth’s orbital plane, so it is rare that Mercury and Earth are on the same level and side of the Sun as they cross our host star.
Royal Observatory Greenwich astronomer Tom Kerss said: “Although Mercury overtakes us several times per year on its relatively quick journey around the Sun, we don’t see transits every time, because Mercury’s orbit is quite highly inclined relative to that of the Earth.
“Fortunately, transits of Mercury are considerably more common than transits of Venus. The next Venus transit won’t occur until 2117.”
The last time Mercury was in transit was in May 2016, but before this the phenomenon occurred in 2006.
Mercury is the smallest planet in the solar system – ever since Pluto was downgraded to a dwarf planet in 2006 – and has a diameter that is just 1/283 of the Sun’s.
As such, it will be impossible to track the movement of Mercury, which will take six hours to complete its transitional journey, without a telescope.
However, online observatory Slooh is streaming the phenomenon live, which you will be able to watch at 12.35PM GMT on Express.co.uk.
NASA said the transit will be most visible to those with telescopes in Americas, the Atlantic and Pacific Oceans, New Zealand, Europe, Africa, and western Asia.
“From our perspective on Earth, we can only ever see Mercury and Venus cross in front of, or transit, the Sun, so it’s a rare event you won’t want to miss!”
The next time Mercury will be in transit will be in 2032.