101 Must-See Cosmic Objects: The Bubble Nebula

William Herschel first observed NGC 7635 in 1787 as a glow around the magnitude 8.7 star SAO 20575 (cataloged earlier as BD+60°2522). In a telescope, the Bubble Nebula looks more like a comma because the full extent of its spherical shell is so faint that it was only discovered through photography. This emission nebula, which is composed of ionized hydrogen energized by an O-type star, is part of a larger complex of glowing gases.

Viewing the Bubble Nebula requires skies free of light poll