In those terms, trigonometric calculations based on 61 Cygni's parallax of 0.314 arcseconds, showed the distance to the star to be 660,000 astronomical units (9.9 ×10 13 km 6.1 ×10 13 mi). The largest unit for expressing distances across space at that time was the astronomical unit, equal to the radius of the Earth's orbit at 150 million kilometres (93 million miles). The star was 61 Cygni, and he used a 160-millimetre (6.2 in) heliometre designed by Joseph von Fraunhofer. The light-year unit appeared a few years after the first successful measurement of the distance to a star other than the Sun, by Friedrich Bessel in 1838.
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