The Pleiades star cluster is one of the most noticeable of all star patterns. To most people’s unaided eyes, the cluster looks like a tiny misty dipper of six little stars. Yet the Pleiades is sometimes called the Seven Sisters. Why?

In Greek mythology, the Pleiads were the seven daughters of Atlas, a Titan who held up the sky, and the oceanid Pleione, protectress of sailing. The sisters were Maia, Electra, Alcyone, Taygete, Asterope, Celaeno and Merope. The Pleiades were sometimes said to be nymphs in the train of Artemis. They were said to be half-sisters of the seven Hyades – the Hyades pattern is another star cluster, near the Pleiades stars.

Modern-day astronomy sees the Pleiades quite differently. Astronomers say this cluster of several hundred stars condensed out of a cloud of gas and dust some 100 million years ago. The Pleiades stars lie nearly 400 light-years away. So we know the cluster’s stars must be very bright for us to see their light across this span of space. These stars are thought to be hundreds of times more luminous than our sun.

So why are the Pleiades called the Seven Sisters, when only six stars can be seen with the eye? In fact, the number of stars you can see within the Pleiades cluster, using just your eye, varies depending on your own eyesight, local atmospheric transparency and light pollution levels. Some people simply see fainter stars than others. It’s possible that early skywatchers, whose skies were darker and clearer than our modern skies, more often saw more than six stars here. Even today, people with exceptional vision see seven, eight or more stars in the Pleiades with the unaided eye.

The Greeks weren’t the only ones to notice this cluster. According to a Polynesian legend, the Pleiades once made up a single star: the brightest in the sky. The Polynesian god Tane disliked this star, because it had bragged about its beauty. It’s said the god smashed the star into pieces, creating the Pleiades star cluster.