Editing the Encyclopedia of Astronomy and Astrophysics

Abstract

Born in Estonia Opik studied at Moscow University, and helped establish Turkestan University in Tashkent, becoming the Astronomer (director) at Tartu Observatory in Estonia. He fled the Red Army by horse cart during the Second World War and went to Armagh Observatory (Northern Ireland) in 1948. His wide-ranging interests are reflected in his discoveries and theories. These include the discovery of degenerate stars, e.g. white dwarfs, in his calculation of the density of o 2 Eridani (1915). He calculated the distance of M31 as 450 000 parsecs from the Sun (1922). He computed by hand evolutionary models of main-sequence stars into giants (1938) over a decade earlier than the computer computations of HOYLE and SCHWARZSCHILD. He predicted the density of craters on the surface of Mars, which was confirmed 15 years later by planetary probes. He put forward an unproven theory of the Ice Ages based on a calculation of changes in the convection in the internal structure of the Sun rather than MILANKOVITCH cycles. Physicist, born in Löd o, Sweden. He was keeper of the observatory and professor at Uppsala where he studied heat, magnetism and optics and examined the spectra of the Sun and auroras. His name is commemorated with the angstrom unit, 10 −10 m, which is used for measuring wavelengths of light and x-rays, and the separation of atoms in molecules and crystals.