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Test out your visual acuity

August 2013: The summer sky holds several naked-eye double stars that, once observed, can tell you something about the sharpness of your eyesight at night.
RELATED TOPICS: DOUBLE STARS
OMearaStephen
Resolving naked-eye double stars presents an unusual visual challenge. To see fine detail, we usually look directly at the object of study so that light falls onto the eye’s fovea centralis — the pit in the retina that is responsible for sharp vision. But the fovea does not have rods, and the cones populating this tiny region are largely ineffective at night.

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