People have been passing around this video for the past few days because it captures an astonishing phenomenon. The newly-built Freedom Tower emits a long, flute-like moaning sound. It's eerie and it's real. But no, it's not the ghosts of 9/11.

The Freedom Tower, built on the site of the World Trade Center's Twin Towers, is in fact a massive aeolian harp, also known as a wind harp. As wind rushes past the metal bars at its top, those bars vibrate, create sound waves, and result in the long, mournful notes you hear in this video. Observers also heard similar sounds coming from the Freedom Tower during Hurricane Sandy, for the same reason.

Over at Doubtful News, Sharon Hill writes:

Stuff like this happens and is likely responsible for many of the mystery "sky noises" that have been hyped over the past two years . . . Please learn some simple acoustics. The wind against objects makes noise – it causes vibrations that generate sound. This sound can be eerie, beautiful or disturbing. But it's natural, not supernatural. I fear that this structure at Ground Zero will forever be associated with spirits of the dead and predict the building will perpetually be "haunted" . . .

Sadly, Hill is probably right. The sounds emitted by the building, already associated with so much trauma, will probably give rise to legends of haunting. Which is doubly sad, because the beautiful sounds of a massive aeolian harp are a tribute to the power of nature and science — as well as a lovely way to memorialize those we lost.

Read more on Doubtful News.