The messenger of the gods is on the move. Today, the planet Mercury will pass in front of the sun, appearing as a tiny black speck for about seven hours. This relatively rare event happens only a dozen times a century 鈥� the last time was a decade ago.
The passage, or transit, of Mercury will begin at 11:12 UTC on 9 May and end at 18:42 UTC, and should be viewable from most of Western Europe and North America, along with all of South America.
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If you want to watch, don鈥檛 look directly at the sun, as you could injure your eyes. If you have glasses left over from last year鈥檚 solar eclipse, put those away as well. 鈥淪pecial glasses are no use because Mercury is so tiny, you need a magnified image to see it,鈥� says at the Open University in Milton Keynes, UK.
Wearing eclipse glasses and looking through a telescope or binoculars is also dangerous, so the best way to view the transit is either with a telescope equipped with a solar filter, or .
Watch it live
If you don鈥檛 have any of that equipment to hand, observatories around the world will be live-streaming the transit, and both the and plan to cover the event in its entirety.
Transits of Mercury used to be a great scientific opportunity, says Rothery, as they allowed astronomers to accurately measure distances in the solar system. Nowadays, they have less scientific value, though: when planets with thick atmospheres cross the sun, astronomers can measure sunlight filtering through, as was the case with the 2012 transit of Venus. But Mercury鈥檚 atmosphere is too tenuous.
鈥淲hen I was a lad in Birmingham I saw the 1973 transit,鈥� says Rothery, but he is particularly looking forward to next week鈥檚 event. 鈥淚t鈥檚 going to be especially important for me this time, because I鈥檓 now involved in the European Space Agency鈥檚 mission to Mercury.鈥�
The spacecraft, which is due to launch in 2018 and arrive in 2024, will study Mercury鈥檚 surface, interior and magnetic field, giving us our best look at the planet now that NASA鈥檚 Messenger probe has been retired and crashed into the surface.
Should you miss the transit, you鈥檒l have to wait until 11 November 2019 for the next one. After that, it won鈥檛 happen again until 2032. The haphazard gaps between transits is a result of Mercury鈥檚 slightly tilted orbit, meaning it doesn鈥檛 often line up exactly between us and the sun.
