The Pleiades is an open cluster in the constellation of Taurus also known as Messier 45, or just M 45. This relatively nearby cluster (about 380 light years) is also known as the Seven Sisters although from cities only the five or six brightest stars are visible. From a dark site, ten or more are visible. The stars are surrounded by nebulosity, observable in photographs taken using long period exposures through telescopes with significant apertures. Due to the particular arrangement of the stars in the cluster and its compact appearance, it is often mistaken for the Little Dipper by those with little knowledge of astronomy.
The Pleiades star cluster M45 (visible from the northern hemisphere) consists of many bright, hot stars that were all formed at the same time within a large cloud of interstellar dust and gas. The blue haze that accompanies them is due to very fine dust which still remains and preferentially reflects the blue light from the stars.
Visible members of the Pleiades are luminous blue or white stars. The cluster contains hundreds of other stars too faint to be visible to the naked eye. This is a young cluster, with an estimated age of about 100 million years, and a projected life of only 250 more million years.
The Pleiades' high visibility in the night sky has guaranteed it a special place in cultures, antique and modern:
- To the Maori of New Zealand, the Pleiades are called Mataariki and their heliacal rising signifies the beginning of the new year (around June).
- The Australian Aborigines believed they were a woman who had been nearly raped by Kidili, the man in the moon. Alternatively, they were seven sisters called the Makara.
- It is said that the Native Americans measured keenness of vision by the number of stars the viewer could see in the Pleiades. Even in historical Europe, especially in Greek circles, the Pleiades were a common vision test.
- In Japan, the Pleiades are known as Subaru.
- In Greek mythology, the Seven Sisters were traditionally identified as: