Cygnus OB2 is an OB association that is home to some of the most massive and most luminous stars known, including Cyg OB2 #8 and Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni.The region is embedded within a wider region of star formation known as Cygnus X, which is one of the most luminous objects in the sky at radio wavelengths. The region is approximately 1,400 parsecs from Earth in the constellation of Cygnus.
The young cluster is one of the largest known, and the largest in the northern hemisphere with some authors classifying it as a young globular cluster similar to those present in the Large Magellanic Cloud. Although it is over ten times more massive than the famous Orion Nebula, Cygnus OB2 is much less well known due to its location behind a massive dust cloud known as the Cygnus Rift, which obscures many of the stars in it; this means that, despite the consensus of its large size, it’s hard to determine its actual properties with its estimated number of massive stars ranging, according to different scientists, for example, from 50 to 100 of spectral type O and its total mass having been calculated as 3*104 solar masses.