As Robert Krulwich says, "it's going to be a very small picture, but we're all going to be in it — all trillions of us on Earth."
NASA's Cassini spacecraft, which is about 898 million miles away in the Saturn system, is turning a camera back toward Earth and will snap away between 5:27 p.m. and 5:42 p.m. ET. According to NASA:
"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."
Still, Slate says:
"When this mosaic of images is completed, it will show Saturn and its rings, backlit by the Sun, with the Earth peeking over its edge. That final image will therefore in principle contain every human in existence. That means you. And me. And everyone you know, don't know, love, are miffed at, are inspired by, in awe of, and who are taller, shorter, sicker, healthier, happier, sadder, slower, faster, the same, and different than you."
If you miss today's shoot, there are similar chances on Saturday. NASA's MESSENGER spacecraft, which is orbiting Mercury, is taking photos of its own that should include Earth. Times for those shots: 7:49 a.m., 8:38 a.m. and 9:41 a.m. ET.
(And yes, we know none of us will actually show up in the photo.)