ROBERT GENDLER / SCIENCE PHOTO LIBRARY ROBERT GENDLER / SCIENCE PHOTO LIBRARY
Globular star cluster M13, optical image. This is an enormous ball of over 100,000 stars that has a diameter of over 150 light years. As with other globular clusters, it lies outside the plane of the galaxy, some 20,000 light years from Earth. The clusters orbit the centre of the galaxy. M13, like other globular clusters, is extremely old. It is thought to be 12 billion years old, which is less than two billion years younger than the universe itself. M13 is found in the constellation Hercules.
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