Belopolskii, Aristarkh

Born July 1 (13), 1854, in Moscow; died May 16,1934, in Pulkovo. Soviet astronomer. Academician of the Academy of Sciences of the USSR (1903).

Belopol’skii graduated from Moscow University in 1877 and was retained there to prepare for the position of professor of astronomy. He photographed the comet of 1884 and the moon during a total eclipse and obtained photographs of the sun’s corona during an eclipse in 1887. He observed the positions of stars with large proper motions and of planets and comets on the meridian circle. He devoted particular attention to photographing the sun. In 1888 he began working at the Pulkovo Observatory, where he was director from 1917 to 1919. In his first years at Pulkovo he conducted studies of Jupiter’s rotation and revealed the different periods of rotation near the planet’s equator and at higher latitudes. He carried out comprehensive investigations of the sun’s rotation by studying the motion of solar faculae and measured numerous photographs of the sun obtained at Pulkovo between 1881 and 1888. Soon after, he began work on determining and investigating the radial velocities of celestial bodies (that is, their velocities along the line of sight). He was one of the first scientists to obtain photographs of the spectra of celestial bodies using spectrographs. (One of the spectrographs at Pulkovo was constructed according to his specifications.) In 1895 he used the measurement of radial velocities in investigating the structure of Saturn’s rings and showed that they consisted of a number of separate small bodies revolving around the planet.

The main purpose of Belopol’skii’s observations was to obtain the radial velocities of bright stars of the second to fourth magnitudes (approximately 200) in order to determine the motion of the sun and to investigate the spectra of variable stars. Belopol’skii did not let by one flare of a new star without investigating its spectrum. He discovered the periodic oscillations of the radial velocities of cepheids. Unsatisfied with the demonstration of Doppler’s principle by observing the radial velocities of stars, he constructed a clever device for its experimental verification. This demonstration, carried out independently of any theoretical constructions, was of decisive significance.

Using a stellar spectrograph, Belopol’skii tried to study the rotation of the sun by spectral means. In 1912 he ordered a special instrument for this purpose, which, however, was made only after the Soviets came to power (1923). Using it, Belopol’skii photographed the spectrum of the sun’s limb according to the plan of the International Union for Solar Studies, whose Russian branch he presided over. During these investigations Belopol’skii observed that the sun’s rotational velocity decreased somewhat between 1925 and 1933, which was corroborated by the observations of other astronomers. He was also interested in comets and studied not only their spectra but also the physical structure and chemical composition of their tails.