If you guessed that I was referring to the Pleiades, you are correct. The small open star cluster, Messier 45, is about 440 Light Years from Earth, relatively close for a star cluster. We are able to see it with the naked eye in Autumn and Winter here in the Northern Hemisphere.

The stars in the Pleiades are young and bright blue, meaning they are very massive and hot. By young, I mean somewhere around a hundred Million Years, about 40 times younger than the Sun. The smears of blue in the above photo show that the cluster is still partially surrounded by its birth nebula, which is slowly being blows away by the radiation pressure of the stars.

Because of the odd shape of the cluster, it is often confused with the little dipper when viewed with the naked eye, especially since the little dipper (Ursa Minor) is not a particularly bright constellation.

For thousands of years, this group of stars has been used as an eye test. Soldiers who could see the seven brightest stars were given positions as scouts or archers. While those with poor eyesight were better suited for other jobs.

If you can see all seven of the brightest cluster stars, you should have around 20/20 vision. If you see less than four, you may want to have your eyes checked.