A crater on the Moon and cosmological model were named as a tribute to him – 149th anniversary of Dutch astronomer Willem de Sitter’s birthday.

In the north of the Moon, on its visible side, not far from the pole crater De Sitter is located near Main, Nansen and Petermann craters. It has 64 km in diameter and 3 km in depth. The crater was named after Dutch astronomer Willem de Sitter who was born on May 6, 1872.

Scholar papers in the fields of celestial mechanics, stellar photometry and cosmology. Over 30 years of observations and studies of Jupiter’s satellites, as well as the new theory of their movement which takes into account the contraction of Jupiter, solar disturbances and interdependent disturbances of satellites: this theory is used for calculations to the present time.

Photometric measurements of stars at the galactic latitudes and systematization of color differences among stars near the Milky Way and galactic pole, which were later explained by concentration of early stars to the galactic plane.

One of the first relativistic cosmological models, which predicted the possibility of space objects’ fast movement and laid the foundation for further theories of expanding Universe, bears the name of de Sitter. De Sitter’s model is a class of cosmological models and solution for equations of general relativity theory with cosmological invariable, which describe the vacuum state. The properties of vacuum state depend on the sign of this invariable and make it very much different from empty vacuum. It is commonly accepted to call the models with negative cosmological invariable anti-De-Sitter ones.

The outstanding astronomer was born in the town of Sneek in the northern part of the Netherlands, almost near the coast, 149 years ago. He graduated from the University of Groningen, one of the largest and oldest universities in the Netherlands.

After having graduated from the university, Willem de Sitter moved from the Northern Europe to South Africa to work at the observatory on the Cape of Good Hope. It was there that the young mathematician started to study Jupiter’s satellites using both heliometric measurements of other astronomers and his own observations, which gave birth to the new theory of their movement.

De Sitter spent two years on the coast of Atlantic Ocean where the Cape of Good Hope is located. In 1899, he came back to his alma-mater and worked as assistant at the Astronomical Laboratory of Groningen until 1907. In 1908, he became of professor of astronomy, while in 1919, the 57-year-old scientist accepted the offer to hold the position of director of the Leiden Observatory. Along with research devoted to Jupiter, the astronomer studied the irregularities of the Earth rotation and explained the slowdown in rotation by tidal friction.

Together with Albert Einstein, Willem de Sitter paved the way for applying the relativity theory to cosmological problem. In 1916, he presented his scholar papers devoted to relativity theory to the Royal Society of London, and they attracted the attention of scientific community to Einstein’s general relativity theory.

Willem de Sitter died on November 20, 1934 in Leiden, where he was working for the last 26 years of his life.

Photo on the homepage:  trv-science.ru

Based on articles from astronet.ru, krugosvet.ruredday.ru