NGC6888 and the Soap-Bubble nebula

About three years have passed and now it is time to revisit the Crescent Nebula again with a longer focal length. In fact the primary goal was to also capture the Soap Bubble Nebula with somewhat more contrast so I doubled the integration time on Oxygen this time.

As a result this faint planetary nebula, which was discovered in 2008 by Dave Jurasevich and catalogued as PN G75.5+1.7, is now much more defined:

In contrast to their name, planetary nebulae do not relate to planets by any means. In fact these are shells of ionized gas ejected from giant stars at the end of their life. Not all planetary nebulae expose such a circular shape like the Soap Bubble Nebula, but this explains why these have been mis-categorized as planets by early telescopes for their similarity to gas planets.

Next to this faint nebula several dark molecular clouds can be observed, potentially forming new stars in the distant future.

The much more prominent Crescent Nebula is quite a different kind of object which also deserves a closer look:

The Crescent Nebula, or NGC6888, is an emission nebula, ionized by a, so called, Wolf-Rayet Star in the center. A Wolf-Rayet Star is a rare massive star which lost its outer shell, so exposing its core. A surface temperature way higher than conventional stars result in extreme radiation, in addition large mass quantities are constantly ejected with velocities up to 4000km per second. Wolf-Rayet stars expose various emission lines in their spectrum while the spectrum of regular stars only show absorbtion lines from the outer layers.

It is assumed, that the Crescent Nebula is the ejected shell of that star.