The ephemeral monument to those we lost during the 9/11 attacks, Tribute in Light, will be turned on tonight at sunset, which will be around 7:11 p.m. The lights representing the Twin Towers of the original World Trade Center will then fade into dawn tomorrow.

The lights have been tested over the past week, leading many New Yorkers to pause and think about the 16th anniversary.

That time of year

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The project, designed by John Bennett, Gustavo Bonevardi, Richard Nash Gould, Julian Laverdiere, Paul Myoda and lighting designer Paul Marantz, was put together by the Municipal Art Society and Creative Time, and was first lit on the six-month anniversary of the attacks. The MAS continued to present Tribute through 2011; from then on, the 9/11 Memorial and Museum has been carrying on the beloved tradition.

"It is an emotional response more than anything…the towers are like ghost limbs, we can feel them even though they’re not there anymore." Laverdiere and Myoda had said.

The MAS says, "The memorial was originally going to be called the Towers in Light, but MAS received feedback from 9/11 families that a name paying tribute to the lives lost rather than the buildings that had once stood would be a more powerful remembrance," and notes, "The Tribute in Light rises four miles into the sky and can be seen from 60 miles away. As of 2002, the two arrays cast the strongest shaft of light ever projected from earth into the night sky."

The lights—"88 7,000-watt xenon light bulbs positioned into two 48-foot squares, echoing the shape and orientation of the Twin Towers," the 9/11 Memorial says—are located just south of the World Trade Center at West and Morris Streets, on the roof of the Battery Parking Garage.

"The lights are best viewed when it is completely dark," says the 9/11 Memorial and Museum. The Memorial plaza will be open to the public until midnight today.

If you see the lights switch on and off, it's because they are trying not to unduly confuse migrating birds.