Abstract
Bessel was the first to successfully detect the annual parallax of a fixed star (61 Cyg) in 1838. Shortly after this, Struve and Henderson detected that of α Lyr and α Cen, respectively. In the case of Bessel, the details of the detection are given in the original paper. However, regarding the parallax theory, which is the basis of the post-measurement analysis, only the theoretical formulae are described, and their derivation is not shown. In the case of Struve, there are only preliminary reports. Furthermore, in the case of Henderson, although the calculation formula for obtaining the annual parallax value are shown, the derivation thereof is not described. It is possible that for the researchers of the parallax at the time, there was no need to show the derivation, but for us, three centuries later, the theoretical basis on which the annual parallax value can be calculated remains unclear in both cases. In view of this situation, Bessel’s theoretical formula of parallax and the formula of Henderson’s annual parallax are derived, and the theoretical basis is clarified. Furthermore, through numerical reproduction, calculation was performed independently. The results obtained are in close agreement with the values described in the original papers, confirming the validity of the respective theoretical formula and calculation formula.
