Messier 13 or M13 (also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules or the Hercules Globular Cluster) is a globular cluster of about 300,000 stars in the constellation of Hercules.
It is located at right ascension 16h 41.7m and declination +36° 28'. With an apparent magnitude of 5.8, it is barely visible with the naked eye on a very clear night. M13 is 25,100 light-years away from Earth.
The Arecibo message of 1974, designed to communicate the existence of human life to hypothetical extraterrestrials, was transmitted toward M13. The reason was that with a higher star density, the chances of a life harboring planet with intelligent life forms, were believed to be higher. Even though the message was transmitted, M13 will no longer be in that location when it arrives. The sending of the message was more of a technological demonstration, rather than an actual attempt to contact life.