NASA's Cassini spacecraft has sent back stunning images of Earth and its moon, showing our home planet from more than one billion kilometres away.

The Saturn probe took advantage of a rare opportunity to point its cameras back towards Earth on Friday, capturing images of Saturn's rings with Earth just a pale blue dot 1.44 billion kilometres in the distance.

It was the first time that Cassini's highest-resolution camera was able to record Earth and the moon as two distinct objects.

"Cassini's picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth," said Cassini project scientist Linda Spilker.

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This image of Earth and the moon was taken by NASA's Cassini spacecraft on July 19, 2013. (NASA/JPL-Caltech/Space Science Institute)

Cassini, named for the Italian-born astronomer who discovered four of Saturn's moons, has orbited the planet since 2004 but it typically can't take photos of Earth because it also means pointing the cameras towards the blinding sun.

Friday also marked the first time NASA was able to give advance warning of an interplanetary photo opportunity, and it encouraged North Americans to take part in its "Wave at Saturn" social media campaign. 

North America and part of the Atlantic Ocean were the only illuminated parts of Earth at the time, and NASA says more than 20,000 people came out to wave at Saturn and post pictures of themselves online.

"It thrills me to no end that people all over the world took a break from their normal activities to go outside and celebrate the interplanetary salute between robot and maker that these images represent," said Carolyn Porco, leader of the Cassini imaging team.

From that enormous distance, Earth itself is only 1.5 pixels wide in the photos, and the illuminated part is even smaller.

The wide-angle image of Earth is part of a planned photo mosaic of Saturn's ring system, which NASA says will take several weeks to assemble.