[It may take a minute to load, it's a big file.]
Wow! You can see the Sun's rotation over the four hour interval these pictures were taken, and then the Moon flashes by. The Moon is dark because it's between us and the Sun, so were seeing the unlit side (I have a diagram showing an approximation of the geometry of this event on my other page about it).
Moreover, scientists can use images of the sharp-edged Moon against the Sun's disk to check on the optics of the observatory. That information can be used to sharpen the images even more. So this is fantastic, fantastically beautiful, and fantastically useful, too.
Tip o' the sunglasses to NASAGoddard.