NASA's long-delayed mission to put humans back on the moon has launched.

After four postponements, Artemis 1 took off from Kennedy Space Center at Cape Canaveral in the extremely early hours of Wednesday.

Here's what you need to know about the historic space endeavour.

What does Artemis hope to achieve?

The mission is made up of three stages.

The first is a 42-day uncrewed flight around the moon. It will test the huge rocket and the Orion spacecraft that astronauts will eventually travel in.

While in space it will deploy 10 CubeSats (a type of miniaturised satellite), which will perform a variety of work in deep space, from studying how radiation affects yeast DNA to hunting for water ice on the moon.

Weather is a big focus of the test mission, with galactic cosmic rays presenting the biggest risk to future crews.

Newly built space weather centres will research solar wind - charged particles released from the Sun - and solar fluxes (concentrated sunlight), as well as coronal mass ejections (large expulsions of plasma and magnetic field from the top layer of the Sun).

A new lunar vehicle will also combine the best from the historic Apollo moon buggies and Mars rovers, allowing astronauts to pilot them in person and remotely.

Orion will fly 60 miles above the moon at its closest, and during re-entry weeks later will emerge into the Earth's atmosphere at 25,000mph before splashing down off the California coast.

Cameras inside and outside of Orion will share images and video throughout the mission.

If all goes to plan, it will have been in space longer than any human craft in history without docking to a station.

A crew will strap in and blast off for the first time for more testing during Artemis 2. The four astronauts have so far not been named, but this stage is pencilled in for 2024.

Lasting about eight to 10 days, they will do a lunar flyby before returning to Earth.

Humans will finally land on the moon again during Artemis 3, with NASA saying the crew will include the first woman and person from an ethnically diverse background.

The timeline depends on how well the previous missions go, but it's currently slated for 2025.

NASA hopes to build a base camp and conduct annual missions and use it as a test bed for even more ambitious missions, starting with getting a human to Mars.

Any fun facts about the mission?

Ancient mythology aficionados will have clocked that the mission is named after the Greek goddess of the Moon and twin sister of Apollo. She was the goddess of the hunt, the moon, and chastity.

The Orion capsule - named after a constellation of stars - will have just mannequins and a soft toy on board.

The mannequin captain is called Commander Moonikin Campos, who will sit in the commander's seat throughout.

A Snoopy soft toy will also float around the Orion capsule as a zero gravity indicator.

How powerful is the Artemis 1 rocket?

The 98-metre Space Launch System (SLS) is the most powerful rocket NASA has ever built and in this crucial testing phase it will fly further than any spacecraft built for humans: 40,000 miles past the far side of the moon and 280,000 miles from Earth.

The megarocket's 8.8 million pounds of thrust at launch is 13% more than the Space Shuttle, and 15% greater than the Saturn V rocket used on the Apollo missions.

Each of the two boosters generates more thrust than 14 four-engine commercial airliners, according to NASA, and will fire for 126 seconds, providing more than 75% of the vehicle's thrust before they break off.

It's also powered by four RS-25 engines, with the outbound trip to the moon taking several days.

When was the last time a human was on the moon?

Almost 50 years ago: it was Apollo 17 in December 1972 - about three and a half years after Neil Armstrong made history with the first moon walk.

With President Kennedy's big goal achieved, the final three Apollo missions were cancelled and NASA's funding cut.

NASA hopes that Artemis will see humans back on the moon in 2025 - but that will be the third part of a trilogy of launches which starts this week.

While Artemis 1 is unmanned, Artemis 2 - currently tipped for 2024 - will see humans launched into space for a lap around the perimeter of the moon before returning home. It will be the deepest humans have ever been into space.

Artemis 3 will come after that, and will see the first woman land on the moon.