In 1974, a group of scientists and government officials sat in silence in the jungles of Puerto Rico.

They were staring up at the afternoon sky.

And then a strange noise.

A little bit like TV static, but also a little bit eerie, ethereal, just two warbling notes over and over and over.

For almost three minutes, the noise continued, blasting through the speakers.

Some people were moved to tears.

Others stood up and began to gravitate towards this unfathomably big structure.

Three towers, with blinking red lights, a 900-ton platform suspended high in the air between them.

And in the center, nestled into the ground, a curving dish, as wide as three football fields.

It was a massive telescope, sending out radio signals into space.

The very first time humans had intentionally sent a message out to whoever or whatever might be out there.

A message saying, we are here.

I'm Dylan Thoris and this is Atlas Obscura.

A celebration of the world's strange, incredible, and wondrous places.

Today, we visit Puerto Rico's Erasibo Observatory and its enormous telescope.

A site loved and lost to both scientists and everyday Puerto Ricans.

That's after this.

Up until 2016, Erasibo was the world's largest radio telescope.

It could detect radio waves from space and use them to create maps of the cosmos.

And it could also send those waves out into space.

What they were sending into the sky that day in 1974 was called the Erasibo Message.

It was a series of radio pulses beamed into space.

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