1835−1836

Wilhelm Struve measured for the first time in the world the distance of the star from the Earth (the star Vega in the Lyra constellation).

Large-scale geodetic measurements, during which a very high degree of accuracy in measuring angles was achieved, made the researchers in the end of the first third of the 19th century think of applying trigonometry also in determining the distance of stars from the Earth. Until then there were no reliable data. To establish the distance of the star, it was simpler to measure the annual parallax or the angle between the positions of the star after a period of half a year. Even in the case of the closest stars this angle was so small (a fraction of a second of an arc) that before building the Fraunhofer refractor it was not possible to measure the annual parallax. Almost at the same time with Struve, Freidrich Bessel (1784-1846) in Königsberg and Thomas Henderson (1798-1844) in Cape Town measured the annual parallax of two other stars (61 Cyg and α Cen). The Struve`s result was rather exact; the annual parallax was 0.125 seconds of the arc and the distance was 26.1 light years; the result today is: 0.123 seconds of the arc and 26.5 light years. Struve himself had doubts about his results and made later new calculations which were less accurate.

The star Vega in comparison with the Sun
The scheme for getting the angle of parallax