NGC 6940 is an open cluster in the constellation Vulpecula. The cluster is nearly a billion years old and it is located 2 500 light years away.
NGC 6940 has hundreds of members. The cluster is quite scattered and in between its members are also visible field stars. For example, two bright stars, an 8.6 mag B8III giant star at the NE edge and a 9.1 mag A0III giant at the SW corner of the cluster are too young to be true members of NGC 6940 and are probably background stars. The brightest star of NGC 6940 is the red giant FG Vulpeculae, a semiregular variable star whose magnitude ranges from 9.0 to 9.5 every 80 days approximately. NGC 6940 is rich in red giants, more than 20 according to WEBDA database. Based on the spectroscopic analysis of twelve of them, the cluster age was estimated to be 1.1 billion years, with a turn-off mass of 2 M⊙. Its metallicity is close to that of the Sun. In NGC 6940 have been detected 8 variable stars whose variability is consistent with the delta Scuti variables.
