M39 is a large, very loose, collection of relatively young, bright stars.  The cluster spans a diameter a little larger than that of the full Moon.  The estimated age of the cluster is between 200 and 300 million years.  The cluster contains at least 30 stars and is located in the constellation of Cygnus the Swan.  It lies relatively nearby, by astronomical terms, at a distance of about 800 light-years. 

The above mosaic is an assembly of 6 separate images.

¹http://apod.nasa.gov/apod/ap090412.html