The deep black center of totality is caused by the moon, but you might never know that since the moon itself is not visible. It is just too close to the blazingly bright sun to see, especially just before and just after totality. Think back to when you were looking at the partially eclipsed sun with your eclipse glasses. Did you see the moon? No. You saw the portion of the sun that was not blocked by the moon, but you didn’t actually see the moon. No, even when 99% eclipsed, the sun is too bright to allow you to see the moon.
Totality, on the other hand, is a different story. During totality, the sun’s photosphere (the bright portion that would hurt your eyes if you stared too long) is completely blocked. Of course, this allows us to see the main attraction of totality: the corona. However, with the photosphere out of the way, it is also possible to see the moon during totality. If you don’t believe me, check out the image that I’ve included here. Look closely and you can see the faint details of the familiar full moon. Pretty cool!
Personally, I could not see the face of the moon with my naked eye, even through binoculars. It was only revealed to me later in this four-second exposure, which was taken about half way through totality. The long exposure causes the corona to be overexposed, but the face of the “man in the moon” is easily visible. Just in case you’re suspicious, I did not create this image in Photoshop by overlaying a picture of a full moon on top of the total eclipse. Note that you can also see the bright star Regulus as a small dot on the far left side of the frame. Some pink portions of the chromosphere are also visible around the edge of the moon in a couple of places.
Since the moon is completely in shadow, the faint light illuminating its surface is due to earthshine (i.e., sunlight that is reflected off the earth and back on to the moon). You have probably noticed earthshine if you have ever gazed at a crescent moon. Earthshine is responsible for the faintly illuminated portion of the moon that should be black, but isn’t quite completely black. If you’re not familiar with it, check it out during a crescent moon. It is easiest to see earthshine during the phases of the moon nearest a crescent. Or, if you really want a challenge, you can wait until your next total eclipse. That is how I like my earthshine! (Which gives me an idea to celebrate the eclipse: earthshine whiskey distilled right here in East Tennessee with this picture on the label!)