Basically, because the moon rotates counter-clockwise to us.
I'm sure y'all knew that, but it had me puzzled.
UPDATE: Greenwich will experience a 70% eclipse, best time to view, 2:45 PM I don't remember the exact year: 1971? * But we had a partial eclipse in town then, and it was eerie. We were playing basketball in the driveway at Gilliam Lane, and it gradually grew darker and darker, and the birds, who we hadn't even noticed until their absence, suddenly went silent. Very cool experience, and one you might want your own kids to experience, if you can lure them outside and away from their smart phones.