Determination of secular polar motion from astronomical observations: Priority of Aleksandr Orlov

The aim of this article is to draw attention to the priority of the well-known astronomer and geophysicist, member of the Academy of Sciences of Ukraine A.Ya. Orlov (1880–1954) in the determination of the following parameters describing the secular motion of the earth’s poles: speed (4 mas/year) and direction (69° west). These results (1954) are based on the astronomical observations from 1900 to 1950 with zenith telescopes at international latitude stations. Orlov is well known in the world astronomical community as the founder of the Poltava Gravimetric Observatory, the Main Astronomical Observatory, and the national research school of global geodynamics. However, his pioneering work on secular polar motion is little known worldwide. At present, Orlov’s estimates for secular polar motion have been verified by century-long observations (1900–2012) obtained with different telescopes at many observatories worldwide and by different, both astronomical and space-based, methods (LLS, VLBI, GNSS, etc.).