M52 Open Cluster, NGC 7635 The Bubble Nebula in Cassiopeia M52 is a large open cluster located in the Milky Way. With an overall brightness of about magnitude 7, it contains about 200 stars, the brightest of which is magnitude 8.2. The cluster is about 35 million years old, but it's distance is not well known with estimates ranging from 3,000 to 7,000 light years. It was discovered by Charles Messier on September 7, 1774. NGC7635, the Bubble Nebula, is located about 35 arc minutes southwest of M52. In space it is 10 light-years wide, and it is located about 11,000 light years from the Earth. The Bubble is formed from a fast stellar wind of ionized gas coming from the massive Wolf-Rayet star BD+602522, which is the brightest star inside the bubble at the upper left. As the wind comes off the star, it pushes the surrounding gas in the area into a giant sphere. The high-energy ultra-violet light from the star then ionizes the gas, causing it to fluoresce and glow. The star is some 25 to 40 times as massive as our Sun and thousands of times brighter. It is shedding most of its mass in this stellar wind in the latter stages of its life cycle which will one day end in a supernova explosion.