Wave at Saturn -- Blog by Jo Pitesky
Wave at Saturn -- Blogs
Earth From Saturn
By Jo Pitesky
July 8, 2013
Watching all the preparation for the upcoming opportunity for Cassini to photograph Saturn with Earth in the background reminded me of a famous NASA image from more than 44 years ago, back during the Apollo era-- December 24, 1968.
Even now, with all the pictures I've seen of the Earth from space, this image of Earthrise from the Apollo 8 mission is still one of my favorites. I love the contrast with the lunar surface, but most of all I love how this picture feels like a casual vacation snapshot. It's not the big glamour shot showing the full Earth in all its glory-it's just, you know, home. Many other people feel the same way. You can easily find books, articles, and documentaries about the enormous impact of this very first full-color view of Earth from space taken by a human. Everyone on Earth could see how fragile the Earth was, and how small it was compared to the great expanse of space . Since I was a small child at the time, not yet besotted with all things space, I didn't have any dramatic reaction to the Apollo Earthrise. My parents were used to thinking of the Earth as looking like an old-fashioned geography class globe, so they were stunned to see the beauty of the Earth. Me? I've just always viewed the Earth as a blue jewel set against a black velvet background.
We've come a long way since then. The Apollo 8 astronauts snapped this picture from a mere quarter-million miles away from Earth. Cassini will be capturing its Earth portrait from about 3,600 times more distant. We don't hold the record for "Most Distant Image of Earth" -- that honor belongs to Voyager 1's Pale Blue Dot image -- but it's still impressive.
Even though we're much farther away, the Cassini image will be returned to Earth much more rapidly than its Apollo predecessor. All of the bits making up the Cassini Pale Blue Dot will arrive via the Deep Space Network within 24 hours after the image is created. Earthrise was captured with a film camera, so first there was the "drive" to the film processor (it took Apollo 8 two and a half days to travel from the Moon back to Earth), not to mention getting the film developed and processed. Cassini scientists will need to process and calibrate their image, but at least they don't have to work in a darkroom with smelly chemicals.
Cassini's image might win for speedy delivery, but Apollo wins for ease of planning. Basically, there was none! The astronauts were on their fourth orbit around the moon, dutifully following their schedule and taking pictures of the lunar surface. No one had thought to take a picture of the Earth until the Apollo 8 crew saw the beauty of the scene and snapped the picture.
On Cassini, we can't be that spontaneous. To paraphrase Voltaire, with great distance comes great complexity. Planning for pretty much every observation carried out by Cassini takes years, and the Cassini Pale Blue Dot is no exception. The project's scientists and engineers started preparing for taking this picture three years ago.
In our activity timeline listing what's happening on the spacecraft, it's just another entry known primarily as "VIMS_195RI_HIPHASEC001_PIE ."1 That's another thing the Cassini image has in common with Earthrise, which NASA initially named "Image #14-2383" -- boring official names for jaw-dropping images.
I hope that Cassini's new Pale Blue Dot image inspires you to look at other views of the Earth from space. There've been many more pictures of our home taken from space in the intervening years. We've gathered together a gallery some of our favorites -- all taken from spacecraft not orbiting Earth. If you have another image that we've missed, get in touch with us using our feedback page, and we'll add it to the list.
1In case you were wondering: VIMS is the instrument making the request, 195 is the orbit number, RI is the target (short for "Rings"), HIPHASEC is the VIMS team's shorthand for saying this is a high phase (meaning not fully illuminated) version C and PIE indicates that this is a so-called "pre-integrated event" (meaning that it is especially high priority, since it was placed into the timeline of events before other activities were integrated into the plan) AND that the instrument named at the beginning is the one doing the detailed design of how to point the spacecraft during the observation.
Jo Pitesky is a member of the Cassini Flight Team, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif.