Hubble Gallery - NGC 6751

NGC 6751 is an unusual planetary nebula around 6500 ly away in the constellation of Aquila. Planetary nebulae have nothing to do with planets - their name comes from a time when telescopes were only able to discern them as round objects in the night sky and thus they appeared similar to planets. They are in fact shells of gas thrown off by stars of masses similar to that of our own Sun, when the stars are nearing the ends of their lives. The loss of the outer layers of the star into space exposes the hot stellar core, whose strong ultraviolet radiation then causes the ejected gas to fluoresce as the planetary nebula.
The Hubble observations were obtained in 1998 with the Wide Field Planetary Camera 2 (WFPC2) - the image was then processed through several filters to highlight the different gases. Blue regions mark the hottest glowing gas whereas orange and red show the locations of cooler gas. The nebula is expanding at a speed of about 40 kilometers per second (25 miles per second), and is currently some 0.8 ly in diameter.