In an emission nebula located in constellation Cygnus (swan), 5000 light years from Earth. The nebula has 25 light years (!) in diameter. This constellation, as well as the nebula is lying on the plane of our home galaxy Milky Way. Therefore there are so many stars visible.
The picture was processed by bi-color technique – this means that the picture is assembled from two narrow band images: hydrogen alpha (Ha) and ionized oxygen (OIII). Ha was inserted into red channel and OIII into green and blue.