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After setting up what may have been the largest group photo in history, NASA has now released the image -- a long-distance shot of Earth taken from over a billion kilometres away.

On Friday evening, NASA encouraged all space enthusiasts to 'wave at Saturn,' as the Cassini space craft captured a photo of Earth from 1.44 billion kilometres away as it orbited Saturn.

Cassini got the rare chance to take the photo because Saturn was in the foreground of the image, blocking out the sun and allowing the spacecraft's sensitive camera to point toward Earth without being damaged by solar rays.

The stunning wide-angle photo shows Saturn and its distinctive rings, with Earth marking a bright, pale-blue dot in the bottom right hand corner of the frame -- a lonely planet suspended in a dark blue sea.

In images taken by the NASA spacecraft Messenger, also on Friday, the moon can also be seen as it orbits around Earth.

Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said Earth is much too far away for anything or anyone -- including space geeks waving from their back yards -- to be visible in the image. But that doesn't take away from its importance.

“We can't see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19," Spilker said in comments on NASA's website.

"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."

Cassini was in the far reaches of the solar system when it took the picture as part of a mission to make a composite, or mosaic, image of Saturn. With the sun backlighting the planet, astronomers had a rare chance to study Saturn and its rings with greater visibility than normal.

It was a coincidence that Earth was to make its way into the frame, essentially 'photobombing' the image of Saturn.

It is expected to take several weeks before the full composite image of Saturn is released, as scientests need to stitch together many images taken at varying light levels and geometric positions.

At the same time Cassini was recording images of Saturn and Earth, the Messenger spacecraft was orbiting Mercury as part of its mission to search for natural satellites around the planet.

Members of the team working on that project recently began looking for a similar opportunity to capture Earth from a great distance and discovered that the planet would fall within its lens on the same day as Cassini.

As a result, two images of Earth were captured on the same day.

"That images of our planet have been acquired on a single day from two distant solar system outposts reminds us of this nation's stunning technical accomplishments in planetary exploration," said MESSENGER Principal Investigator Sean Solomon of Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y.

"And because Mercury and Saturn are such different outcomes of planetary formation and evolution, these two images also highlight what is special about Earth. There's no place like home."

Earth has been photographed twice before from a similar distance.

The first and most distant image of Earth was taken 23 years ago by NASA's Voyager 1 spacecraft, which captured the planet from 6 billion kilometres away.

The other was Cassini's image taken in 2006 from 1.49 billion kilometres.