A prominent open cluster in Taurus, popularly termed the Seven Sisters, and also known as M45. The cluster spans over 1½° of sky and contains about 100 stars, the brightest of which is 3rd-magnitude Alcyone. Several other members are visible to the naked eye. Its true diameter is about 13 l.y., although there may also be scattered outliers. The cluster lies nearly 400 l.y. away and is about 80 million years old. Its stars are embedded in a reflection nebula, which is now thought to be the result of a chance encounter rather than the nebula being the remains of the gas cloud from which the stars formed.