This dazzling image is of the Rosette Nebula, a rose-shaped nebula in the Unicorn constellation. The nebula's central star cluster is so bright that it was discovered a century and a half before the rest of the nebula.
The Rosette Nebula is located between 4,500 and 5,000 light-years away in the constellation of Monoceros, which translates to the Unicorn. The nebula's less flowery name is NGC 2237, and it's home to one of the brightest star clusters in the night sky. NASA explains:
At the center of the flower is a cluster of young stars called NGC 2244. The most massive stars produce huge amounts of ultraviolet radiation, and blow strong winds that erode away the nearby gas and dust, creating a large, central hole. The radiation also strips electrons from the surrounding hydrogen gas, ionizing it and creating what astronomers call an HII region.
This cluster is so bright that it was discovered a full 150 years before anyone noticed the nebula surrounding it. English astronomer John Flamsteed discoverd NGC 2244 around 1690, but it wouldn't be until 1840 that John Herschel was able to spot the much fainter nebula. The cluster remains a favorite of amateur astronomers, as it's easily visible with even a small telescope or decent pair of binoculars.
You can see the full, uncropped image taken by NASA's WISE telescope below. You can click on either image for a closer look.