From Kepler to Parallax

Abstract

Although lacking an observatory, Kapteyn was not idle. Some of his work was non-astronomical. He carried out extensive research looking for possible periodicities in the weather on the basis of measurements of growth-rings in trees and together with his brother Willem, a professor of mathematics in Utrecht he made detailed studies of a particular set of mathematical series. But he also performed clever astronomical work. He wrote an extensive article in which he developed a new numerical method for solving Kepler’s equation and another one on the determination of the altitude of the celestial pole free from systematic errors, vindicating the method with observations in Leiden. He also used telescopes in Leiden to measure stellar distances (parallaxes) from accurate timing of meridian passage. These measurements were surprisingly accurate when compared to current determinations. His work on polar altitude resulted in his first contact with David Gill at Cape of Good Hope.