The clockwise rotation of polarized light when passing through a substance, or the degree to which this rotation occurs.
From dextro- 'right,' rotare 'to turn,' and -tion suffix. A fundamental term in 19th-century optical chemistry for characterizing molecular properties.
Scientists discovered that if you shine polarized light through sugar water, it twists—the amount it twists is proportional to how much sugar is there, so you can measure sugar concentration through rotation!
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