Architect Santiago Calatrav designed the Oculus with a retractable glass ceiling. On every September 11th the glass ceiling is removed letting the sun in with the most intense sunshine entering the building at 10:38AM which is the moment the second tower fell.
"The glass spine of the building, which is made of blast-proof glass and ribbed with rectangular frames, was built to fully retract, leaving a long, curved, open skylight that stretches the length of the space, like a giant eye that is just waking up. It opens on September 11th at 8:46 a.m., the time the first plane hit the Trade Center, and is positioned, Stonehenge-like, to frame the sun at 10:28, when the second tower fell. It also frames 1 World Trade, a building that can, depending on the angle and light and weather, look a little too shiny, or oddly proportioned, or just plain ominous. In a clear view from the Oculus floor, however, on a blue-sky day like today, and like September 11, 2001, it looks like a dream."