North is to the right.
The Bubble Nebula,
cataloged as NGC 7635 and Sharpless 162, is an HII emission region
in the constellation Cassiopeia, at a distance of about 11,000
light-years. The "bubble" is created by the stellar wind from a
massive young, hot, 8.7 magnitude central star. William Herschel
discovered the nebula in 1787.
These false color images were acquired with Ha, SII and OIII filters
mapped to the RGB channels respectively. The colors of top image
more closely follow the Hubble Palette, with the color channels
pretty much stretched to equal levels. The presence of sulfur,
hydrogen and oxygen are clearly shown. Red indicates the
presence sulfur, green hydrogen and blue oxygen. With no color
manipulation, the image would be basically green, due to the
dominance of hydrogen.
The lower image
was additionally processed to produce a
color motif made
popular by the Hubble imaging team.