Astronomy Picture of the Day Index - Nebulae: Planetary Nebulae

APOD: 1999 October 31 - The Cat's Eye Nebula
Explanation: Three thousand light-years away, a dying star throws off shells of glowing gas. This image from the Hubble Space Telescope reveals The Cat's Eye Nebula to be one of the most complex planetary nebulae known. In fact, the features seen in the Cat's Eye are so complex that astronomers suspect the bright central object may actually be a binary star system. The term planetary nebula, used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, high resolution images reveal them to be stars surrounded by cocoons of gas blown off in the late stages of stellar evolution. On planet Earth, of course, cats and other creatures may be on the prowl tonight. Keep your eyes peeled and have a safe and happy Halloween!

APOD: 1999 March 21 - M2-9: Wings of a Butterfly Nebula
Explanation: Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays as they die. In the case of low-mass stars like our Sun and M2-9 pictured above, the stars transform themselves from normal stars to white dwarfs by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula that fades gradually over thousand of years. M2-9, a butterfly planetary nebula 2100 light-years away shown in representative colors, has wings that tell a strange but incomplete tale. In the center, two stars orbit inside a gaseous disk 10 times the orbit of Pluto. The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance. Much remains unknown about the physical processes that cause planetary nebulae.

APOD: 1999 July 3 - NGC 2440: Cocoon of a New White Dwarf
Explanation: Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly", but not for another 5 billion years. The above false color image and was post-processed by Forrest Hamilton.