A lot of people use glasses.
Are you one of them?
Well, you should know that vision testing in ancient times was as important as it is today.
But how did they test vision?
The most famous naked eye test vision used the double star system of Mizar and Alcor in the Ursa Major.
The ability to perceive the separation of these two stars was considered a test of good vision and was called the "test".
It was believed that Mizar and Alcor were not gravitationally bound.
Though, astronomers reported that Alcor is itself a binary, consisting of Alcor A and Alcor B, and that Alcor binary system is bound to the Mizar quadruple system – making six stars in all, where we see only two with the eye.
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