The world is being asked to look up on Friday and smile in the direction of the ringed planet, Saturn.
The Cassini probe, in orbit around the gas giant, is going to take a picture of Earth, and the imaging team wants everyone to wave and smile.
Because of the great distance to Saturn, our home will appear as a mere pixel in the final photo.
But Cassini scientist Carolyn Porco says it is a moment to "celebrate life on the Pale Blue Dot".
"Waving time" - the period when the spacecraft's cameras will be operating - starts at 21:27 GMT and ends at 21:42 GMT (22:27-22:42 BST).
These timings include the 80 minutes it will take reflected light from the surface of the Earth to travel the nearly 1.5 billion km (900 million miles) to reach the outer Solar System.
Dr Porco's Ciclops imaging team will be producing a large mosaic of Saturn and its ring system on Friday.
Earth will appear as small speck in the lower-right of the final picture.
It is likely to be several days before the first images are processed and released.
Inspired in part by the Cassini team's plans, scientists working on the Messenger probe at Mercury will also be picturing Earth on Friday and Saturday.
Messenger will see Earth as it scans the skies for any previously unrecognised objects that might be circling the innermost world.
Timings for these pictures are 11:49, 12:38, and 13:41 (all GMT) on both Friday and Saturday.