Pleiades star cluster M45, optical image. This is the nearest major star cluster to Earth at just 440 light years away. It contains over 500 young stars, thought to be between 75 and 150 million years old. The blue reflection nebula surrounding the stars is not the remnants of the nebula from which they formed, as was once thought, but instead a gas and dust cloud that the nebula is passing through by chance. The particles in it reflect the light of the stars. The Pleiades cluster is in the constellation Taurus.