A skylight would run the length of the station building. The roof was originally designed to mechanically open to increase light and ventilation to the enclosed space. In a nod to the Libeskind concept, the Oculus was built to maximize the effect of the autumnal equinox rays (coinciding with the skylight opening on or around September 11 every year). On the actual anniversary of the attacks, the skylight would open for 102 minutes to commemorate the duration between the time the first tower was hit and the collapse of the second tower. If needed, the skylight could also be manually opened to provide air ventilation.