A space phenomenon will take place on May 9 when the planet Mercury passes between the Earth and the Sun.
The transit will be visible from Earth and appear as though a black dot is making its way across the Sun.
The UK, western Europe, eastern US and Canada will see the entire seven and a half-hour transit, as will most of South America, and westernmost Africa.
Mercury will appear 150 times smaller than the Sun.
Further west they will see it only from sunrise, and further east only before sunset. Australia will have to sit this one out altogether.
In the UK it will take place soon after 12pm and end at about 6.42pm, so fingers crossed for clear skies. If all fails though, the European Space Agency is streaming the transit here. There will also be Q&A sessions with experts and related presentations.
Anyone hoping to get a good look at the rare occurrence will need to be careful so there’s no damage to their eyes. Forget eclipse glasses as they won’t offer the magnification needed. Mercury, the solar system’s smallest innermost planet, measures about 3,000 miles across so it would be too small to spot.
You’ll need binoculars or telescopes equipped with proper solar filters to protect your eyes. Seriously, don’t try to look at the Sun without them.
Mercury’s transit of the Sun happens about 13 times in a century.
The last time Mercury crossed directly between the Earth and Sun was in 2006 (which wasn’t visible from the UK), and it won’t happen again until 2019 – and then until 2032, although the UK won’t be as well placed to watch those.
Louis Mayo, program manager at Nasa’s Goddard Space Flight Centre in Maryland, said: “It’s a big deal. Astronomers get excited when any two things come close to each other in the heavens.”
Scientists at Nasa will be using the transit to learn more about the tiny planet’s atmosphere.
The US space agency will train three spacecraft on the Sun for the transit and share images online from Nasa’s Solar Dynamic Observatory.
If you’re *safely* watching at home, look for Mercury initially south of the Sun’s equator. The planet might appear as though it’s hardly moving, but in reality it will be zooming past the Sun at nearly 106,000mph.