Relating to the measurement of the sun's position, size, or the distances and angles between celestial objects using a heliometer.
From Greek 'helios' (sun) and 'metron' (measure), plus suffix '-ical' (relating to), describing precision astronomical measurements.
Before telescopes could photograph distant stars, astronomers used heliometers to measure tiny angles in the sky with incredible precision—some of the first measurements proving the Earth really orbits the Sun came from heliometrical observations!
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