HII-Region Sharpless 310: In the prominent constellation of Canis Major, which contains also the brightest star in the sky Sirius, is a very large cloud of ionized hydrogen gas.Such areas are called HII-regions. In this case the brightess of the gas cloud is so low that it cannot be observed, but only made visible by sensitiv cameras with long exposure times.

The image shows the structure and large extent of the cloud, which also carries the catalog designation Sharpless 310. The bright star at the top is Wezen or Delta Canis Majoris.