From Bad Astronomy Blog:
STEREO-B caught what astronomers call a transit — the passing of one celestial body in front of another — but in this case it’s OK to call it what it is: a solar eclipse, when the Moon passes in front of the Sun.
On Earth, the Sun and Moon are about the same size in the sky. Every person on Earth, since as long as there have been people, have seen the Sun and Moon about the same size in the sky. The only exception I can think of were the Apollo astronauts, who, as they approached the Moon, saw it as being bigger than the Sun.
But no one, ever, has seen the Moon pass in front of the Sun when the Moon was significantly smaller than the Sun. No one.
Take a look at the video. It is a unique and beautiful view. Looking through NASA's releases you can find a multitude of stunning images of our solar system, galaxy, and beyond.