Aksel Kipper

Aksel Kipper (5 November 1907 – 25 September 1984) was an Estonian astrophysicist and academician, known for theoretical work on the continuous spectra of planetary nebulae and for his role in establishing the modern Tartu Observatory at Tõravere.

Early life and education Kipper was born in Viljandi. After graduating in 1930, he defended a master's thesis on the open cluster Messier 39.

During his directorship, Kipper was a principal organiser of the modern observatory complex at Tõravere, built to replace the ageing city-centre facilities; it opened in September 1964 and became Estonia's main centre for astronomical research. Following institutional reorganisation in 1973, he became the first director of the Institute of Astrophysics and Atmospheric Physics in Tõravere and retired from the post in 1974, continuing research work thereafter.

Scientific work Kipper's research included the physics of stellar atmospheres and pulsating stars, including work on shock-wave formation in stellar outer layers.

He is especially noted for explaining the origin of the continuous spectrum of planetary nebulae using two-photon processes in hydrogen and related radiative-transfer effects, publishing key works in 1950 and 1952. In later decades he worked on magnetohydrodynamical processes in stars and developed ideas on turbulence in cosmic magnetic fields; in his final period he turned to cosmological questions involving electromagnetic and quantum properties of cosmological space and their relation to redshift phenomena.

Awards and honours Kipper joined the International Astronomical Union in 1955. He received the honorary title of Merited Scientist of the Estonian SSR in 1957 and the Nõukogude Eesti preemia (Soviet Estonia Prize) in 1967. He was awarded the Karl Ernst von Baer medal in 1976.

He was decorated with the Order of the Red Banner of Labour (1946 and 1965) and the Order of the Badge of Honour (1977).