July 19, 2013 was a very special day in the history of humanity. From a distance of 898.414 million miles (1.445858 billion kilometers) from Earth, the Cassini spacecraft made this stunning mosaic of the ringed planet as it eclipsed the Sun. The result is nothing less than breathtaking:
There is simply no way to adequately convey the beauty of this image in mere words. Instead, I invite you to view the colossal 9000×3500 pixel mosaic itself. Take a moment for it to load and just scroll around for a while. (Be sure to check out the annotated version of the mosaic as well.)
Cassini was “behind” Saturn in the sense that it was on the side of Saturn opposite the Sun. This gave the Cassini team an opportunity to create a mosaic of the entirety of Saturn and its rings backlit by the Sun.
The planet itself appears in silhouette, but not completely. Notice that part of Saturn’s dark side is illuminated by light reflected off the rings themselves. In other words, “Ringshine.”
Cassini was about 17 degrees below the plane of the rings, allowing the rings to appear as an ellipse in this view. And that’s a good thing because it really allows us to explore the rings in a very unique way.
The outermost E-ring appears diffuse and ghost-like. It’s created by geysers of ice crystals erupting from Enceladus. If you zoom in on the left side of the image, sure enough you’ll spot Enceladus with geysers erupting!
There are several other moons to be seen in this image, and some background stars as well. But as amazing as this image is, what makes it truly interesting is that you, me, and everyone on Earth are in it.
The day Earth smiled
At the bottom right of the mosaic is a tiny pale blue dot. That’s us. That’s you and me and the whole of humanity right there on a tiny, pale blue dot.
We are 898.414 million miles (1.445858 billion kilometers) in the background in this image. Zooming in reveals both our home planet and Moon. That’s all of us, right there, looking up toward Saturn, and smiling.
That’s what makes this image of Saturn so special, and why July 19, 2013 is a special day in the history of humanity. Human beings from all over that blue dot looked up toward Saturn while Cassini was taking its picture, smiled, and waved.
Here’s looking at you, Saturn!
Update 2013-11-14: Emily Lakdewalla from the Planetary Society has an excellent walkthrough of the image and explains why things appear the way they do in the image. It is well worth your time to have a watch (be sure to go full screen and HD so you can really spot the details):