NEW YORK (AP) — At sundown, two vertical beams of bright blue light shot upward through the darkened New York City sky, evoking the twin towers in an annual tribute visible for miles.

The “Tribute in Light” public art installation first shone six months after the Sept. 11 attacks and has been repeated each anniversary since, with the twin columns reaching up to four miles into the sky from dusk to dawn.

The beams are comprised of 88 xenon light bulbs, each 7,000 watts, positioned into two 48-foot squares on the roof of a parking garage south of the 9/11 Memorial. They can be viewed from a 60-mile radius.

The 9/11 Memorial and Museum presents the display to honor those who were killed and celebrate the spirit of the city.

For the 20th anniversary, buildings throughout New York also planned to light up their facades and rooftops in blue.