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 o2 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.