The Bubble Nebula (NGC 7635) is the smallest of three bubbles surrounding the massive star BD +60° 2522 in the constellation Cassiopeia (RA 23h 20.7m Dec +61° 12'), and part of the gigantic bubble network S162, created with the help of other massive stars. As fast-moving gas spreads out from BD +60° 2522, it pushes surrounding sparse gas into a shell. The energetic starlight then ionizes the shell, causing it to glow. The nebula is about 6 light-years across and visible even with a small telescope.