Lit from within by a young, hot star, this cosmic bubble is not to be missed.
The expanse of glowing gas known as the Bubble Nebula, energized by a hot star within, imaged in the dense Cassiopeia Milky Way. Credit: Adam Block
The far northern sky holds its richest region in Cassiopeia, a splendid area of bright Milky Way stars and gas. One of the greatest nebulae in the far north is NGC 7635, the Bubble Nebula, so named for its remarkable spherical bubble visible in images.Â
This object is an emission nebula with a reasonably high surface brightness, making it visible in moderate-sized scopes under a dark sky.Â
The Bubble glows at about 10th magnitude and spans 15’ by 8’. It lies 8,000 light-years away.Â
The faint bubble that gives this object its popular name, a challenging part of the brighter nebula, is illuminated by a hot, magnitude 8.7 star: SAO 20575, a young sun whose fierce radiation is ionizing the bubble.Â
The surrounding field is rich: Nearby lie open clusters (M52 and others) and a slew of nebulae including NGC 7538, Sharpless 2–157, and IC 1470.Â
