The night sky is a ephemeral tapestry filled with nearby planets and far off stars. A quick glance upwards on a dark night will warrant more stars than imaginable. Still, there are elements of this eternal artwork that lie even further away than the stars seen from Earth. While our own star’s neighbors have either long dissipated to the rest of the galaxy or did not exist at all, wild gatherings of other stars can be seen in clusters that dot the night sky. For the most part, these clusters contain stars that formed about the same time as each other. Imagining the night sky from a planet within one of these clusters is overwhelming, yet tranquil, as the night sky would possess luminescence like a thousand planets all shining at once.
There are two varieties of clusters that have been found. Open clusters, such as the Pleiades, contain at most a few hundred young stars that are relatively spread out, though close enough to appear as a disseminated group from the humble vantage point of Earth. On the other end of the spectrum there are globular clusters which are more like tiny, spherical galaxies than normal star groupings. Before Andromeda was discovered to be a galaxy it was believed to be a massive globular cluster on the edge of known space, though now it is known that Andromeda has many of its own globular clusters.
One of the most beautiful and visible star clusters, M13, makes its appearance high in the western sky in the early evening. To find it, look to the west and count around 45 degrees. With the naked eye, this feature will appear like a fuzzy normal star, hardly distinguishable from the closer elements of the night sky. Through a telescope or binoculars, it will begin to unveil its true nature as a field of tiny stars rather than one large star. To give an idea of the immense size of this cluster, it is estimated that at least a hundred thousand stars exist within the sphere that is 145 light-years across. As a reference, if Earth today were to exist on one side of M13, the first episode of I Love Lucy would be located slightly more than one-third of the way across. The cluster is around 25,000 light-years away from Earth in the constellation of Hercules. Be sure to read again next week as the focus shifts to the more tangible and visible open clusters that are closer to home.
Peace and may the stars shine brightly in your skies.