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.
6 thoughts on “Testing Eyesight and Being Mistaken for the Little Dipper for Thousands of Years”
I thought Pleiades was identified as Messier 45, M45, not Messier 42 as you have stated at the beginning of your article.
Ah good call – thanks for catching the typo!
I just happened on your blog because I was trying to figure out if I saw the Little Dipper this morning or if it was something else. I am digging the information; I hope that by clicking “Notify me of new posts by email” that I’ll be able to subscribe. Keep up the good work!
Great article. Though I got confused in the beginning to read this as a treatment for weak eyesight informative article. but yes. it is still worth.