Credit: ESA/Hubble, NASA, A. Sarajedini
This star-studded image taken by the NASA/ESA Hubble Space Telescope shows NGC 6717. It is located more than 20,000 miles from Earth in the constellation Sagittarius. NGC 6717, also known as a globular or spherical cluster, is composed of a tightly bound collection of stars by gravity. Globular clusters have more stars in their center than in their fringes. This image shows this well. The sparsely populated edges in NGC 6717 contrast sharply with the bright collection of stars at its centre.
Some interlopers are also visible in the center of this image. These bright stars are located between Earth and the cluster. These bright foreground stars can be easily identified by the crisscrossing diffraction spikes, which form when their light interacts to the structures that support Hubble's second mirror.
The constellation Sagittarius can be found in the same region of the night sky that the Milky Way's center, which is filled by light-absorbing gas or dust. Astronomers refer to this absorption as "extinction". This makes it difficult to study globular clusters close the galactic center. Astronomers used a combination Hubble's Wide Field Camera 3 with the Advanced Camera for Surveys to determine NGC 6717's properties.
