The Pleiades star cluster, M45, lies at an approximate distance of 380 to 435 light years and is one of the most recognized clusters in the sky.  It is visible to the unaided eye even in light polluted skies.  In moderate skies, 6 of the brightest stars shine in a distinctly "dipper" shape.  As many as nine stars are readily visible in darker skies. The cluster consists of approximately 500 stars of varying magnitude and extends across a diameter of about 2 degrees.  This equates to the diameter of 4 times that of the full moon.  This beautiful star cluster is imbedded in a cloud of gas and dust that displays in long exposure images and shines by reflected light from the bright cluster stars.  The interesting thing about this cloud is that it is not actually part of the star cluster.  M45 is passing through this cloud of dust and gas at an approximate speed of 11,000 kps.  This was determined by measurements of the relative speed of the cluster stars and that of the nebular cloud.

The Pleiades is also known as "The Seven Sisters". This is a reference to the seven daughters of the Greek gods Atlas and Pleione.

¹ http://www.seds.org/messier/m/m045.html