Image via Wikipedia
Pale blue dot. I have loved that phrase as a description of Earth since I first came across it years ago. It refers to an iconic image of earth we've all seen and Carl Sagan used it as the title for one of his books (probably referring to the image to the right, as opposed to th more famous blue marble image). (Here's the wikipedia description of that book and the wikipedia description of the photo.)
Al Reinert wrote up a short history and discussion of the blue marble image over at The Atlantic recently.
It was the first photograph taken of the whole round Earth and the only one ever snapped by a human being. You can't see the Earth as a globe unless you get at least twenty thousand miles away from it, and only 24 humans ever went that far into outer space. They were the three-man crews of the nine Apollo missions that traveled to the moon between 1968 and 1972, six of which landed there successfully (three men went twice). But only the last three saw a full Earth. In order to see our planet as a fully illuminated globe you need to pass through a point between it and the sun, which is a narrower window than you might think if you're traveling at 20,000 miles an hour.
There's an ongoing dispute among the astronauts on the mission as to who actually took the picture. Rienert points out that it doesn't really matter:
Both men are certain they snapped The Blue Marble Shot and can't believe the other won't admit it. They can get rather snarky about it and that's a shame. They each deserve to be remembered better for their uncontested moments. Schmitt discovered volcanic rocks that proved to be the oldest samples returned from the moon, while Cernan was the last man to walk there, an exit he dignified with humility and grace we can all be proud of. It doesn't particularly matter who took the picture as long as we have it.
The photo itself is lovely.
The Earth was nearing winter solstice at the time so the South Pole was tilted sunward, cupping the planet in a clean white bowl. White clouds swirl north over deep blue oceans and the green middle of the African continent, then a tan arc caps the image with the dry lands of Arabia. All around this perfect colorful circle is blackness so dense it defines infinity. It's an unmistakable portrait of a living world and it is arresting.
So I got an iPad 2 the other day - which probably has more power in it than all the compute power in the devices that carried those astronauts to the moon. I've set the pale blue dot (or blue marble, depending on your preferred nomenclature) image as my background image for now. The pale blue dot is a good reminder to try to keep things in perspective. In another way, the transition from stunning, hard-to-capture image to commodity decoration for handheld gadget is also thought-provoking. I don't really know what to make of that, but ultimately it does please me to see it on my new toy/productivity device.
 I haven't dug up the the exact figures, but it seems likely.