A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas and plasma ejected during the asymptotic giant branch phase of certain types of stars (fewer than about 8 solar massess) late in their life. More massive stars are destined to end their life in a far more spectacular manner [supernova].

Planetary nebula are a relatively short-lived phenomenon, lasting a mere few tens of thousands of years, compared to a typical stellar lifetime of several billion years because of this they are rather rare and there are only about 3000 known examples in our galaxy compared to approx 200 billion stars. At the end of the star's life, during the red giant phase, the outer layers of the star are expelled via pulsations due to rapid fluctuations in the rate of Helium fusion which is extremely sensitive to temperature these fluctuations produce strong stellar winds driving material outwards. The hot, luminous core emits ultraviolet radiation that ionizes the ejected outer layers of the star causing the energized shell to glow forming a planetary nebula. Eventually the star runs out of Helium fuel and because the core is not heavy enough to support fusion of Carbon and other heavier elements this is the end of the line and as the stars core cools the planetary nebula fades leaving a white dwarf. In the deep future this will be the fate of our own star the sun.

(Modified and supplemented from Wikipedia) http://en.wikipedia.org/wiki/Planetary_nebula.

Exposure details

14 x 20 min exposures using a Baader 7 nm Halpha filter.