Sky watch: A message to faraway star cluster

Standing above the eastern horizon after dark at this time of year is the constellation of Hercules - or Heracles, as the ancient Greeks knew him - who represents the immortal strong man who performed eight heroic deeds, as well as the 12 Labors of ancient Greek mythology.

Hercules is the fifth-largest constellation in the sky, but because it contains no brilliant stars, it's not particularly noticeable. What might be easy to locate, however, are the four stars that form a distorted square, or keystone. This traces the body of the strong man, but finding his appendages can be a challenge to even the most imaginative of stargazers.

In this constellation, not only does Hercules contain an abundance of double stars - pairs of stars that often glow with strikingly different colors - but it's also home to one of our galaxy's most stunning globular star clusters.

The cluster, known by the name M13, lies along the western edge of the keystone. Under a dark sky, M13 is just barely visible to the naked eye, but aim a small telescope in its direction, and you'll be amazed at the thousands of stars concentrated within its spherical form.

It was in the direction of M13 that, in 1973, a three-minute radio message streamed from the newly dedicated 1,000-foot diameter radio telescope in Arecibo, Puerto Rico. Astronomers hoped that, someday, some alien ears might hear it and learn something about us here on Earth.

But no one here is awaiting a response - the message won't even reach M13 for 21,000 years. Then, assuming it's received and deciphered, a reply would take another 210 centuries to reach us!

But that's OK. The message was intended to be like a note in a bottle, thrown by the human race to the cosmic sea. It said, in essence, "We're here." And it might one day let other beings who wonder about their own uniqueness in the cosmos know that they are not alone.

It's all a pretty chilling concept, if you ask me. And equally chilling is that we can see this star cluster with our own eyes on any clear, dark night if we know just where to look.