See the skylight of the World Trade Center Oculus open as a 9/11 memorial

For the second time, the skylight that crowns Santiago Calatrava’s Oculus at the World Trade Center Transportation Hub opened for close to two hours on the anniversary of 9/11, allowing light to flood the main hall of the transit hub. At 10:28 a.m., the moment that the North Tower of the WTC collapsed on September 11, 2001, a beam of sunlight shone across the center of the majestic space.

The retractable skylight wasn’t part of Calatrava’s original plan for the Oculus—initially, he wanted the “wings” themselves to open and close, to mimic the action of a bird in flight—but that was eventually nixed due to budgetary concerns.

But in a way, that worked in the structure’s favor. The memorial as it stands now is more subtle, and thus more poignant; it allows the building itself, and Calatrava’s “bird in flight” concept to shine without spectacle, in keeping with the solemn tone of the day.

“The memory of the victims will be honored and explicitly expressed through the most symbolic and significant element of the project,” Calatrava told the New York Times in 2015.

Here’s what that looked like today—which, much like that September morning 16 years ago, was brilliantly sunny and clear: