Two NASA spacecraft are about to take pictures of the Earth for planetary science research, and the US space agency is encouraging people worldwide to jump into the shot. \"Consider it the first interplanetary photobomb,\" NASA said. The first chance is on Friday, July 19, from 21:27 to 21:47 GMT, when the Cassini spacecraft takes a picture of Saturn as it is backlit by the sun. The Cassini Earth portrait is part of a wider effort to see patterns in Saturn\'s dusty rings. But no need to fix your hair or makeup too much. Cassini will be nearly 900 million miles (1.44 billion kilometers) away when it takes the pictures. And only North America will be in daylight for the shoot. \"While Earth will be only about a pixel in size from Cassini\'s vantage point...the team is looking forward to giving the world a chance to see what their home looks like from Saturn,\" said Linda Spilker, Cassini project scientist at NASA\'s Jet Propulsion Laboratory in Pasadena, California. \"We hope you\'ll join us in waving at Saturn from Earth, so we can commemorate this special opportunity.\" The second photo op will include all of Europe, the Middle East and Central Asia as another spacecraft captures glimpses of Earth in its mission to search for natural satellites around Mercury. Images will be taken by NASA\'s MESSENGER spacecraft on July 19 and 20 at 11:49, 12:38 and 13:41 GMT both days. NASA said it will release pictures the two spacecraft take next week, possibly as early as Monday. In the meantime, space enthusiasts are invited to share their shots on Facebook or on Twitter using the hashtag #waveatsaturn.