Nasa has invited people to look skywards 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 have moved into position to take pictures of Earth, which will appear as a dot.
At the time of the 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 said the snapshots of Earth are part of a bigger effort to study Saturn's shimmering rings and search for moons around Mercury.
It could take weeks to process the images.