The Bubble Nebula is formed around a massive bright blue star,
which is emitting a fast stellar wind of ionized gas. As fast
moving gas expands off the central star, it pushes surrounding
sparse gas into a shell. The energetic starlight then ionizes
the shell, causing it to glow. The nebula, also known as NGC 7635,
is visually located on the edge of the constellation Cassiopeia.
The Bubble Nebula is thought to be a rare example of a very massive
star, with an extremely strong stellar wind, located within a gas
cloud. It can be seen that this outward wind results in an expanding
shock-wave which forms this "bubble" in space. The "bubble" itself
is estimated to be about 10 light years across, more than twice the
distance from the Sun to the nearest star; estimates vary regarding
its distance from earth, with 7100 light years being the most common
figure given.

Note: I Imaged with AP 130 @ F/4.5 with SXV H9 CCD. Guided with SBIG STV.
Luminance consists of 156 minutes with Hydrogen Alpha 13nm filter (6 minute subs).
Red channel is combination of five 6 minute HA exposures and three 10 minute
red filter exposures. Green and blue channels each consists of six
10-minute images.

Total exposure time was 336 minutes. HA portion was done in Sept 2006,
colors acquired October 2006.

Color exposures were filtered through an IDAS LPS filter to combat light
pollution at my SF Bay Area home.