Dreaming in the sky

Imagine being in the time of the Ancient Romans and your dream is to become an archer in the service of the army. However, glasses have not yet been invented and to become an archer you must necessarily have perfect eyesight.

To find out if a candidate met this requirement, he or she underwent an eye test, which you can easily repeat today too.

On a clear, cloudless night, go out to look at the sky in the direction of the Big Dipper. Focus in particular on Mizar, the second star of the neck from the left (in the perspective of this image). Next to Mizar at an angular separation of 12 arc minutes there is Alcor, another star of fourth apparent magnitude.

If with your eyes you can distinguish both stars then you have almost perfect vision and you could have become archers in the time of the Ancient Romans!

If, on the other hand, with the naked eye you see Alcor and Mizar as a single indistinct point, your eyesight is not so good and you would have had to settle for another assignment in the Roman army.

Credit: Akira Fuji.

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