This star-studded image from NASA’s Hubble Space Telescope depicts globular cluster NGC 6717, which lies more than 20,000 light-years from Earth in the constellation Sagittarius.
Globular clusters are roughly spherical collections of stars tightly bound together by gravity.

The bright foreground stars at the center of the image reside between Earth and the cluster, and are distinguished by the crisscross diffraction spikes that form when their light interacts with the structures supporting Hubble’s secondary mirror.

The constellation Sagittarius is in the same area of the night sky as the center of the Milky Way, which is filled with light-absorbing gas and dust. This absorption of light – which astronomers call “extinction” – makes studying globular clusters near the galactic center challenging. To determine the properties of NGC 6717, astronomers relied on a combination of Hubble’s Wide Field Camera 3 and the Advanced Camera for Surveys.

Image credit: ESA/Hubble and NASA, A. Sarajedini larger image