NGC 7635  The Bubble Nebula
and Open Cluster M52

NGC 7635, also called the Bubble Nebula, Sharpless 162, or Caldwell 11, is a H II region emission nebula in the constellation Cassiopeia. It lies close to the direction of the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7 magnitude young central star, the 15 ± 5 M SAO 20575 (BD+60 2522). The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in 1787 by William Herschel. The star SAO 20575 or BD+602522 is thought to have a mass of 10-40 Solar masses.

Messier 52 (also known as M 52 or NGC 7654) is an open cluster in the Cassiopeia constellation. It was discovered by Charles Messier in 1774. M52 can be seen from Earth with binoculars.

Due to interstellar absorption of light, the distance to M 52 is uncertain, with estimates ranging between 3,000 and 7,000 light years. One study identified 193 probable members of the cluster, with the brightest member being magnitude 11.Messier 52 is evaluated at about 35 million years old.