M13, The Great Cluster in Hercules is a really spectacular globular cluster. Visually it is bright when seen through an 8” telescope and is easily the coolest deep space object to observe in the night sky. It is estimated that some 300,000 stars exist in this cluster and that it is only 145 light years in diameter. In 1974 a message, called the Arecibo message, was sent out via FM radio waves towards M13 which is some 25,000 light years from us.
Note: The heading name for this entry is misleading. M13 is super but it is not a super cluster. Super clusters are groups of galaxies not stars, The Milky Way (our galaxy) is part of the Laniakea Supercluster. A idea of the hierarchy starting from Earth would be someting like; Earth — Solar System — Solar Interstellar Neighbourhood - Milky Way Galaxy — Local Galactic Group — Local Supercluster(Laniakea Supercluster) — Observable Universe.