People wave at Saturn as Cassini spacecraft takes pictures of Earth from space

Smile Earth! You're on camera.

NASA is inviting the public to look skyward and wave at Saturn and Mercury in what is billed as an interplanetary photo op.

The Cassini spacecraft in orbit around Saturn and the Messenger craft circling Mercury moved into position on Friday to take pictures of Earth, which will appear as a dot.

At the time of Friday's Cassini photo shoot, North America will be in sunlight. Europe, the Middle East and Central Asia will be illuminated in portraits by Messenger on Friday and Saturday.

Scientists say the snapshots of Earth are part of a bigger effort to study Saturn's shimmering rings and search for moons around Mercury. It'll take days to weeks to process the images.