A precision telescope instrument used to measure very small angular distances or positions of the sun and other celestial objects.
From Greek helios (sun) + micrometer, combining two measurement traditions: solar observation and microscopic-scale precision measurement developed in the 1600s.
This ingenious instrument let astronomers measure angles smaller than the width of a human hair held at arm's length—enabling them to track the sun's position with incredible precision and refine our understanding of Earth's orbit.
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