* Astronomy

The first direct estimate of stellar distances used geometry. In 1838, Friedrich Bessel measured the parallax of the bright star 61-Cygni. This is the seasonal shift in the apparent position of the star on the sky relative to more distant stars as the Earth travels its orbit of the Sun. The shift was only 0.6 seconds of arc, a very small effect, which is in part why it took two hundred years of telescopic observations before parallax to any star was measured. 

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