This is a different moon illusion. You might also like to just look at the lunar eclipse pictures, even if you aren’t interested in the illusion!
Here are some pictures that I took of the lunar eclipse on February 20, 2008. The classic moon illusion that you are most likely already familiar with is the one in which the moon looks much larger than it really is, especially when it is close to the horizon.
What I am demonstrating here is that since we all instantly recognize the moon, and we know it is round, we take the little data we have in our minds about the tiny crescent, and form the rest of the moon in our mind, even though most of the surface of the moon is the same shade of black as the background. This is an example of our mind filling in the blanks for us, and extrapolating the outline of a circle for farther than it really goes.
To see the illusion, just take a look at the moon (taken at different times, and merged together into one lunar eclipse image) and you’ll notice exactly what I’m talking about. Each moon shape appears to be round, but that’s just our eyes. If in fact, the left half of the moon had been bitten off by a giant monster just a few minutes before the eclipse, I’m sure no one would have noticed!
The nice thing about taking the pictures during a lunar eclipse, is that you can see how it progressed through time and the moon was in the exact same place each time.