“Today I saw Mercury.” This terse remark scrawled inside a 16th-century almanac could reflect anyone watching today’s transit of Mercury across the Sun. The winding path this observation took after it was recorded, however, traces a century-long story leading through the transformation of both our understanding of the cosmos and the practice of astronomy itself.
The Great Equatorial Telescope at the Royal Observatory in Greenwich has captured the moment perfectly. Remember, Mercury is passing in front of the sun at about 30 miles per second. But it will take more than seven hours to reach the other side.
I’ve been refreshing the Met Office app all weekend - they were giving cloudy and getting cloudier, but here we are in bright sun under a blue sky, it’s perfect. Several of their astronomy society members have brought large filtered telescopes for the public, but the provisions for the free public event include two Heath Robinson-ish contraptions, viewers which reflect the image captured through a lens focused on the sun, one made of cardboard, one of chipboard, both working perfectly. The event goes on for 7.5 hours. We’re going to keep moving these tracking the sun until we reach the very furthest balcony we have tonight - we’re going to squeeze the last drop out of it.
Astronomer Dhara Patel with the Royal Observatory’ s sophisticated cardboard transit viewer - through which a sunspot larger than the earth is already visible.
Mercury is a really, really strange planet. You wouldn’t want to spend your birthday there, but if you did, you’d at least get to celebrate twice a day, thanks to the planet’s rotation and orbit around the sun.
Hurry and you can still make it along to one of the many transit parties being held by astronomy groups around the country and worldwide.
The Royal Astronomical Society here in the UK has compiled a list of events is here. And the European Space Agency has its own list here. Nasa’s Jet Propulsion Lab has pulled together another list of transit parties in the US.
The smallest and fastest planet in the solar system will cross the face of the sun today and from many parts of the world the whole transit will be visible. All of the UK, most of Europe, and much of the Americas will have the chance to watch from start to finish, with only Australia and far east Asia missing the spectacle, because for them the event takes place at night.
The transit begins at 12.12 BST and ends at 19.42 BST, when the small black dot of Mercury will slide free of the sun’s disc. We will be following the transit live through the day, with rolling footage from the ground and from satellites trained on the sun. Remember that looking directly at the sun can cause permanent damage to the eyes. For this event, astronomers on the ground are using telescopes fitted with special solar filters that make the sun safe to view.
The transit of Mercury happens only 13 or 14 times a century. This will be the best chance to watch the event from the UK until 2049. Join us!