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pl: 61 Cygni
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61 Cygni is significant because Friedrich Wilhelm Bessel determined its parallax in 1838, the first star to have a known parallax.
Examples of well-known stars which are usually referred to by their Flamsteed numbers include 51 Pegasi ( see Extrasolar planet ), and 61 Cygni ( see Parallax ).
In 1838 Bessel won the race, announcing that 61 Cygni had a parallax of 0. 314 arcseconds ; which, given the diameter of the Earth's orbit, indicated that the star is 10. 4 ly away.
If the currently accepted figure of 11. 4 ly ( see 61 Cygni and discussion page ) is correct, Bessel's figure had an error of 8. 8 %.
As well as helping determine the parallax of 61 Cygni, Bessel's precise measurements allowed him to notice deviations in the motions of Sirius and Procyon, which he deduced must be caused by the gravitational attraction of unseen companions.
The first direct measurement of the distance to a star ( 61 Cygni at 11. 4 light-years ) was made in 1838 by Friedrich Bessel using the parallax technique.
But Friedrich Bessel was skeptical about Struve's data, and, when Bessel published a parallax of 0. 314 ″ for the star system 61 Cygni, Struve revised his value for Vega's parallax to nearly double the original estimate.
1.135 seconds.