The apparent shift in a star's position against distant background stars as observed from opposite sides of Earth's orbit around the Sun. This tiny angular displacement allows astronomers to measure distances to nearby stars through triangulation.
From Greek 'parallaxis' meaning alteration or change in position, combined with 'stellar' from Latin 'stella.' The concept dates to ancient Greece, but stellar parallax wasn't successfully measured until 1838 by Friedrich Bessel, proving Earth's orbital motion.
Stellar parallax is the cosmic equivalent of closing one eye, then the other, to judge distance! This tiny wobble—often smaller than the width of a dime seen from 2 miles away—was humanity's first step into measuring the true scale of our galaxy.
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