Messier 39 - or NGC 7092 - is a large open star cluster in the constellation Cygnus, about 800 lightyears away.
Open star clusters are relatively young objects, in astronomical terms. M39 could be as young as 250 million years old. Some globular clusters, for example, are older than 11 billion years old.
Messier 39 can be seen with the naked eye under very dark conditions, and even binoculars and a small telescope will provide a good view of the cluster. Locate it in the sky near bright star Deneb, Alpha Cygni.
Below is a selection of images of Messier 39 captured by BBC Sky at Night Magazine readers and astrophotographers.