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April 5, 2016

Back in 1974, astronomers used the biggest radio telescope on Earth to beam a message to the stars. The message was a simple picture. Among other things, it showed our solar system, the radio telescope, and a stick figure of a human. The astronomers aren’t waiting for a reply, though — their target was the star cluster M13, which is 25,000 light-years away.

M13 is one of about 150 globular clusters in the Milky Way galaxy. It’s a massive stellar “city” — it consists of about 300,000 stars packed into a ball that’s only a few dozen light-years across.

So far, we don’t know whether there are even any planets in M13, much less intelligent life. In fact, only one planet has been found in any globular cluster. Based on the number of planets discovered closer to us, though, it seems likely that M13 does have planets.

And if it does, there’s been plenty of time for life to take hold and flourish. M13 is about 12 billion years old — far older than our own solar system. Indeed, one recent study says that a civilization could easily spread throughout an entire globular cluster; more about that tomorrow. So it’s possible that we might someday hear back from M13 — an ancient city of stars.

M13 climbs into view in the northeast by about 10 or 11 p.m. It’s between the two stars at the top of the Keystone, a lopsided square at the heart of Hercules. Under dark skies, the cluster is just visible to the unaided eye as a hazy smudge of light.


Script by Damond Benningfield

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