NGC 206 is the richest and most conspicuous star cloud in the Andromeda Galaxy, and is one of the largest and brightest star-forming regions in the Local Group.[2] It contains more than 300 stars brighter than Mb=−3.6.[3] It was originally identified by Edwin Hubble as a star cluster but today, due to its size, it is classified as an OB association.[4]
NGC 206 is located in a spiral arm of the Andromeda Galaxy, in a zone free of neutral hydrogen. It contains hundreds of stars of spectral typesO and B. The star cloud has a double structure: one region has an age of around 10 million years and includes several H II regions in its border; the other region has an age of 40 to 50 million years and includes a number of cepheids. The two regions are separated by a band of interstellar dust.[5]