Seeing the Sun in Stereo

I stumbled across these pictures of what was described as a transit of the Moon across the face of the Sun, which I've thrown together into this animation.


Thing is, it doesn't look anything like a solar eclipse as we would see from Earth. The Moon is TINY is comparison to the Sun, so this picture definitely wasn't taken on Earth....but where? It must've been taken much further from the Moon than we are, but then, where's Earth? Not appearing in the picture, for sure! Turns out the picture was taken 4 times further away from Earth than is the Moon. Where's the Earth? Off camera. The pictures were taken by one of the STEREO satellites.

STEREO is a loose but descriptive acronym for Solar Terrestrial Relations Observatory of which there are two. The two satellites are now satellites of the Sun. After launch, they were set into finely-tuned, slighty-different, highly eccentric orbits that brought them to the orbit of the moon. Once the Moon's gravity perturbed their orbits, this slight variance sent the Stereo A observatory out in front of our orbit and closer to the sun and then sent the Stero B drifting behind us and further away from the Sun. Both are now slaves to the Sun, slowly drifting away from us, who will soon settle into their own orbits just ahead and behind us in our yearly dance around the Sun. The two are studying the Sun and its coronal mass ejections.