This picture, snapped by the Apollo 8 astronauts on Christmas Eve, 1968, was described by Galen Rowell as "the most influential environmental photograph ever taken." It's worth noting that this wasn't a planned picture. One of the crew noticed the Earth rising over the limb of the Moon, and grabbed a camera. Without intending to, he made one of the most eloquent statements about the fragility of our common home, ever. Here's another picture like it:
This one was snapped by Jack Schmitt, coming home from the Moon on Apollo 17. It was the first picture ever taken of a full Earth, famously described as the "Blue Marble". Together, these two pictures became icons of the environmental movement of the 1970s. Together, they did more to elevate concerns about pollution than all the words written up to that point.
And neither one would have been possible, had it not been for the application of the most advanced technology available to Man, and the observational training given to the men who flew them.
That's all by way of introduction. I saw a picture earlier today that absolutely stunned me.
This one is from Cassini, in orbit around Saturn. We have a lot of pictures of Saturn, but this one is an image that we would never, ever see from Earth. That's because it's taken from the other side of that planet, a side that we never see. All the rings are backlit by the Sun, displaying details we'd never see, otherwise. And did I mention it's a stunning picture?
If anyone ever asks you why we spend any money on NASA, if anyone ever asks you why space exploration is worth it, show them these three pictures. Even if we never learned anything else out there, the perspectives we've gained by looking back over our shoulder have been immeasurable.