http://www.cnn.com/2003/US/Northeast...ect/index.html

Sounds pretty cool!
"The architect says that having calculated the arc of the sun, a wedge of natural light would funnel visitors to the memorial site, and that every September 11 between 8:46 a.m., when the first tower was struck by a plane, and 10:28 a.m., when the second tower collapsed, no shadows will be cast by his buildings. "