A stray piece of a SpaceX rocket is travelling through space at about 5,400mph (8,690 km/hr) and is on course to collide with the Moon.
Impact is expected around 07:35 BST - here's how we got here
The crash won't be visible to the naked eye, but people with access to a sophisticated telescope may see a flash from the lunar surface.
In a statement, Nasa spokesperson Jimi Russell says the collision "poses no danger to Earth"
An estimated one million kilograms of debris will blast into space after the 4,000kg (8,800 lb) rocket part makes impact
The SpaceX Falcon 9 rocket was launched in January 2025, with its upper section - now headed for the Moon - being discarded
How a SpaceX rocket ended up hurtling towards the Moon
The story began in January last year, when a Falcon 9 rocket blasted off from Florida carrying two lunar landers into space.
The rocket's job was to fire its upper stage hard enough to send both landers out of Earth orbit and onto a path towards the Moon, and it succeeded.
But the spent stage was left drifting in a long, looping orbit that swung it out towards the Moon and back again.
Over the following 18 months, the gentle gravitational tug of the Earth, Moon and Sun - along with even the faint push of sunlight itself - gradually altered its path.
Astronomers tracking the object eventually worked out that those small nudges had put it on a course toward the Moon, picking up speed by the day and heading for an almighty crash.
No danger to Earth from collision - Nasa
The collision between the Moon and a drifting SpaceX rocket is not thought to be dangerous, including to Earth, according to experts.
Nasa spokesperson Jimi Russel says while Nasa will continue to observe the site of impact for scientific purposes, "there is no danger to Earth".
Nasa scientists are planning to collect lunar data from the event and refine techniques for tracking objects in space.
"It's something really huge smashing into the Moon. It's not remotely dangerous, we can just watch the show," says Dr Matt Bothwell, public astronomer at the University of Cambridge.
