Pleiades, M45, or Seven Sisters, approx 440 light years from the Earth, is an open star cluster located in the constellation of Taurus. The Pleiades are at the moment passing through a cloud of interstellar medium, causing a blue glow around the stars.

Technical info:
TS 80mm f6 APO triplet refractor - Canon 40D - exposure (57x180sec) ~3 hours