Globular clusters resemble stellar jewel boxes featuring roughly spherical assemblies of countless closely-packed stars. This example, NGC 6717, was discovered by William Herschel in 1784 and is located some 20,000 light years from Earth in the constellation Sagittarius. It is one of at least 150 globular clusters orbiting the Milky Way and a spectacular target for the Hubble Space Telescope, which captured this composite image using the Wide Field Camera 3 and the Advanced Camera for Surveys. The brighter stars with criss-cross diffraction spikes, caused by light interacting with the support vanes holding Hubble’s secondary mirror, are much closer to Earth and not part of the cluster.
Located some 22,000 light-years away in the southern constellation of Musca (The Fly), this tightly packed collection of stars — known as a globular cluster — goes by the name of NGC 4833. Globular clusters are thought to contain some of the oldest stars in our galaxy. This NASA/ESA Hubble Space Telescope image shows the dazzling stellar group in all its glory.