- M 52 (NGC 7654) and NGC 7635 (Bubble Nebula)
This is a beautiful pairing of dissimilar objects in the constellation Cassiopeia. M 52 is a rich open cluster containing up to 6000 member stars. The bright yellow-white star along the right side of the cluster is a giant of spectral class G8 that is a true member of the cluster. Most of the stars in the cluster are class B or O, with their blue-white color an indicator of the relatively young age of the cluster (estimates range from 25 to 165 million years). The uncertainty of the age may indicate that the cluster has undergone two phases of star formation. With a visual magnitude of 6.9, M 52 is an easy target for binocular viewing.
NGC 7635 is an emission nebula located approximately a half-degree to the west of M 52. The distance to NGC 7635 is estimated to be around 7100 to 11,000 LY, while the distance to M 52 is estimated to be around 3000 to 7000 LY. Thus, these two objects are probably not physically associated. What makes this nebula remarkable is the bubble-like feature it contains, which gives it it's name. The "bubble" is an expanding shell of gas driven outward by the stellar winds from the hot, young star BD+60 2522 (located slightly below the apparent center of the bubble). The hydrogen gas in the bubble and surrounding nebula is ionized by the strong UV radiation from this star, causing the gas to glow in red Hα emissions. The bubble has a physical diameter of around 6 LY.
M 52 was accidently discovered by Charles Messier in 1774 while he was observing a comet. NGC 7635 was discovered by William Herschel in 1787.
My image contains another open cluster. The loose collection of stars below M 52 is Czernik 43. It has around 15 stars spread over an area around 7 arc-min across.
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