The Bubble Nebula lies not far from the open cluster M52 in Cassiopeia. The bubble is formed by stellar winds from the hot magnitude 8.7 central star pushing out material in the large molecular cloud within which the star formed. The star appears off center within the bubble because the nebula is denser on one side than the other, resulting in asymmetric expansion. Intense UV radiation from the star causes the surrounding nebula to glow, particularly at the hydrogen-alpha wavelength. 

Telescope: Celestron Compustar C14.

Exposures: Ha:L:R:G:B=240:335:60:60:60 = 12 hours 35 minutes total exposure at f/8.3.

This image was published in the October, 2013 and the August, 2016 issues of Astronomy Magazine. It was also selected as Editor's Choice on SkyandTelescope.org.