What will happen when a SpaceX rocket collides with the Moon?

The impending collision - predicted to happen at about 02:35 EDT (06:35 GMT) on Wednesday - is expected to captivate astronomers, both amateur and professional.

"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.

"It's going to impact and its going to send up a huge plume of dust, maybe 50km into the air or more, and that's going to spread sideways over time," Bothwell said.

Given the Moon's lack of atmosphere and far weaker gravitational pull, the moment of impact will be "more impressive than any [similar] explosion on Earth", Bothwell said.

Nothing will slow the object down, like the atmosphere would do here on Earth - and nothing will prevent the estimated million kilograms in debris from rocketing up into space.

While the impact will not be visible from Earth with the naked eye, people with access to a sophisticated telescope may be able to see a flash radiating off the Moon's surface, Bothwell said.

More significant would be the educative potential of the impact, Bothwell noted. He said this moment would present a unique opportunity to study what happens when an object hits the Moon.

Scientists are therefore gearing up to watch the event closely.

Big telescopes in the Americas, plus Nasa's Lunar Reconnaissance Orbiter and South Korea's Danuri probe, will track the flash, plume and new crater, and a citizen‑science project is signing up keen amateurs to film the impact too.

By catching the dust plume in action, astronomers hope to turn this accidental crash into a useful experiment.

Watching how much material gets thrown up, how high it goes and how it falls back should sharpen their models of lunar impacts – and even give clues about what lies just beneath the surface at the impact site, where fresh subsurface material will be exposed for the first time.