Tribute In Light, the annual 9/11 light installation, will return tonight in honor of the 18th anniversary of the September 11th attacks. The tribute produces two vertical columns of light meant to signify the Twin Towers rising high above the Manhattan skyline. As in years past, the lights will be visible from sunset tonight (around 7:12 p.m.) until dawn the following morning.

The Memorial Plaza at the 9/11 memorial site will be open to the public from 3:00 p.m. until midnight, though you won’t need to be there to view the lights. They will be visible from up to 60 miles away, which includes parts of Connecticut, Long Island, Northern New Jersey. As the 9/11 Memorial puts it, the Tribute In Light has become “an iconic symbol that both honors those killed and celebrates the unbreakable spirit of New York.

Here's a look at the lights, located on the roof of the Battery Parking Garage, south of the World Trade Center at West and Morris Streets, being tested earlier this week:

The display has been an annual tradition for more than 15 years. The blue beams of light first appeared on the six-month anniversary of the attacks, March 11, 2002, funded by the Lower Manhattan Development Corporation. They have returned every September 11 since 2003. According to the National September 11 Memorial & Museum blog, “The beams reach four miles into the sky and at 7,000 watts, are the most powerful shafts of light ever projected from Earth.”

No wonder, then, that the lights have been known to confuse birds. Several years ago, a multiyear study found that the lights have affected the migrations of more than a million birds, who sometimes become so confused by the artificial light that they fly directly into one of the city’s reflective glass buildings. "It's not that birds are stupid or anything," Dr. Susan Elbin, one of the authors of that study, told Gothamist in 2017. "It's that they don't know glass is a barrier, and they haven't evolved to deal with artificial light at night."

For this reason, the tribute lights are often turned off for 20-minute periods in order to allow birds trapped in the beams to fly away. The NYC Audubon is regularly on the scene to help monitor migrating birds and make sure they weren't getting trapped.