Mercury is set to pass in front of the Sun in a rare event that has had huge importance to the history of astronomy. But you shouldn’t watch it.
While the sight of Mercury’s transit is one of the most spectacular and important things that can be viewed from Earth, doing so with the naked eye can be dangerous. But there is still a range of ways that you can watch the important alignment.
Watching at home is dangerous because it relies on looking straight at the Sun. You wouldn’t actually be able to see the event with the naked eye anyway – or using kit like eclipse glasses – because the dark patch of Mercury is swamped by the bright light of the Sun.
Seeing the event would instead require a telescope. But that’s an even worse idea: it serves only to amplify the effect of the sun’s light on your eyes, and could cause lasting and painful damage or even blindness.
So it’s important to use a telescope with solar filters that keep out the dangerous rays. Most telescopes in people’s homes won’t have those – so it’s best to head somewhere with more specialist kit that will allow you to see the sun itself.
You can find a list of all of the places holding events on the internet. Astronomical societies across the country are holding events, all of which can be found on this map.
Or you can watch online. NASA and ESA are hosting live streams - and they'll even have them from space, which will help avoid any problems caused by clouds.
The event starts at 12.12 UK time and will end at 19.42. Mercury will appear in the middle of the Sun at 15.57.
As well as being beautiful – when viewed properly – transits have been incredibly important to the history of astronomy. They were once used to calculate the size of our solar system, and the distance between us and its other objects - and now they are one of the ways that we find the other objects further out in the universe.
