There have been only two images of Earth from the outer solar system in all the time humankind has been venturing out into space. The first and most distant was one was taken 23 years ago by NASA's Voyager 1 spacecraft from 4 billion miles (6 billion kilometers away), showing Earth as a pale blue dot . The other opportunity was Cassini's image in 2006 from 926 million miles (1.49 billion kilometers).
NASA is encouraging everyone to go outside and wave at Saturn during the event. Two NASA spacecraft, one studying the Saturn system, the other observing Mercury, are maneuvering into place to take pictures of Earth on July 19 and 20.
The image taken from the Saturn system by NASA's Cassini spacecraft will occur between 2:27 and 2:42 PDT (5:27 and 5:42 p.m. EDT, or 21:27 and 21:47 UTC) Friday, July 19. Cassini will be nearly 900 million miles (nearly 1.5 billion kilometers) away from Earth. NASA is encouraging the public to look and wave in the direction of Saturn at the time of the portrait and share their pictures via the Internet.
The Cassini Earth portrait is part of a more extensive mosaic -- or multi-image picture -- of the Saturn system as it is backlit by the sun. The viewing geometry highlights the tiniest of ring particles and will allow scientists to see patterns within Saturn's dusty rings. Processing of the Earth images is expected to take a few days, and processing of the full Saturn system mosaic will likely take several weeks.
Inspired in part by the Cassini team's plans to obtain a picture of Earth, scientists reexamined the planned observations of NASA's MESSENGER spacecraft in orbit around Mercury. They realized Earth is coincidentally expected to appear in some images taken in a search for natural satellites around Mercury on July 19 and 20. Those images will be taken at 4:49 a.m., 5:38 a.m. and 6:41 a.m. PDT (7:49 a.m., 8:38 a.m. and 9:41 a.m. EDT, or 11:49, 12:38, and 13:41 UTC) on both days. Parts of Earth not illuminated in the Cassini images, including all of Europe, the Middle East and Central Asia, will appear illuminated in the MESSENGER images. MESSENGER's images also will take a few days to process prior to release.
NASA hopes this event will get more people interested in learning about Saturn and to get out and see the ringed giant for themselves. Click here to find out how to see Saturn.
For more info check out NASA's Wave at Saturn webpage.