by Mikhail PANASYUK, Dr. Sc. (Phys.&Math.), Director, Scientific Research Institute of Nuclear Physics named after D. Skobeltsyn (NIIYaF), Moscow State University; Yevgeny ROMANOVSKY, Dr. Sc. (Phys.&Math.), head of the department of the same institute; Vladimir TULUPOV, Cand. Sc. (Phys.&Math.), senior researcher of the same institute

This year the scientific community marked the 90th birthday of Prof. Alexander Lebedinsky, a leading figure in the field of astrophysical and geophysical research. His range of interests covered the origin of stars and planets, northern lights, cosmic and geophysical studies by space probes, preparation of experiments and development of instruments for unmanned interplanetary stations.

Alexander Lebedinsky was born in Geneva on January 7, 1913. Five months later the parents took him to the southern Russian city of Simferopol in the Crimea. His father was a barrister and his mother a housewife. He finished the middle school at 16 and at 19 graduated from the Department of Physics and Mathematics of the Crimean Pedagogical Institute. For the next several years he was a school teacher in Sevastopol.

His keen interest in problems of astrophysics and geophysics made him enter in 1932 the post-graduate course at the Chair of Astrophysics of what was then the Leningrad (St. Petersburg) State University. His tutor- a young, but already prominent scientist, Prof. Nikolai Kozyrev - later recalled that "the rate of progress of my young undergraduate was such that I myself had to do my best to keep up with him."

During his post-graduate course Alexander Lebedinsky studied problems of the theory of thermal convection in the terrestrial and solar atmospheres and that became the subject of his thesis for the degree of Candidate of Sciences which he defended in 1937. Next year he took the post of a senior lecturer (docent) of the Chair of Astrophysics. He continued his studies even in the tragic conditions of the Nazi siege of Leningrad and completed in 1941 a big work "Convections in Atmospheres" in which he examined the role of energy transfer in stars and atmospheres of planets. He relied on notions based on the Benard model of convection foci as being the closest to reality. Using his own theory for different conditions (with what were called transparent and non-transparent foci, or cells) with respect to the Sun and the earth atmosphere, Dr. Lebedinsky was able to assess energy fluxes, temperature gradients and other parameters. His monograph was submitted for a degree of Doctor of Sciences which he won in 1941. In 1943 he received the post of professor of the Chair of Astrophysics of the Leningrad University (which was evacuated from the besieged Leningrad to Saratov). From 1944 he worked in cooperation with Prof. Lev Gurevich, an expert in theoretical physics, and the range of their interests covered magnetic fields of solar spots, flares of novas and supernovas,

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Cepheids (pulsating stars, whose intrinsic light variations are very regular, and supergiants), planetary and stellar cosmogony. In their studies of the magnetic- hydrodynamic phenomena on the Sun, the two Russian scholars, independently from the Swedish Nobel Laureate (1970) Prof. Hannes Alfven, approached the concept of "in-freezing" of magnetic field into the conductor gas. Lebedinsky and Gurevich formulated and applied their theory of thermal nuclear explosion when the rate of energy release is more dependent on temperature than the rate of heat emission.

In their works on the origin (cosmogony) of planets, which were largely influenced by the hypothesis of Acad. Otto Schmidt on the origin of the solar system, the two scientists analyzed physical processes which had to take place in the protoplanetary cloud in the course of its evolution.

In the hypothesis of Acad. Schmidt the central place was given to the capture by the Sun of the gas-and-dust cloud from which planets were later formed. That, however, was not of primary importance for the two researchers. The really important thing was that planets could form as a result of the evolution of the gas-and-dust disc-a possible fragment of a protostar not necessarily captured by the matter. Proceeding from this assumption, two researchers were able to explain the differences in the chemical composition and masses of planets of the terrestrial group and planets-giants, the law of planetary distances-the regularity of variations of the mean distances of planets from the Sun, minor excentricities of orbits, etc.

In his works on the cosmogony of stars Lebedinsky voiced several important ideas on gravitational condensation of gas and star systems dynamics. In examining the process of protostar contraction and its becoming a star, the scientist stressed the important role of molecular hydrogen-a major component of the present-day theories of stellar cosmogony. Several of the works focus on the evolution of dust and gas in diffuse nebula and accentuate the impossibility of their prolonged existence near hot stars.

The name of Prof. Lebedinsky is inseparably associated with the studies of aurora polaris ^* . He was one of this country's pioneers investigating this puzzling natural phenomenon. In 1948 Prof. Lebedinsky designed and tested an original wide- angle camera C-180 which made it possible to photograph automatically the sky from zenith to the horizon and obtain the spectra of aurora polaris from brief exposures of only several minutes. This camera has been used at scores of Russian ground stations in the Arctic and Antarctic under the programs of the International Geophysical Year (1957 - 1958) and the International Year of the Quiet Sun (1964 - 1965).

As chairman of the Aurora Polaris Section of the Interdepartmental Committee of the International Geophysical Year, Prof. Lebedinsky took an active part in developing related research programs and supervized preparations for observations and the processing of the obtained data. At the end of 1957 he took a long trip to inaccessible regions of this country's Far North, rendering assistance to the staff of stations located there. A high degree

^* See: L. Lazutin, "Northern Lights", Science in Russia, No. 4, 2001. - Ed .

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Spatial location of the oval of aurora polaris: S - Sun; P - geomagnetic pole; 1 - oval of aurora polaris; 2 - projection of the oval on the earth surface.

of synchronization of their operations using the C-180 cameras all across the network (with error +/-2.5 s) made it possible to study the development of aurora polaris.

The analysis of the Soviet, and later global stations network changed substantially the accepted notions on the location of zones of aurora polaris. It was demonstrated that they are observed at all longitudes at one and the same time. It was also established that their discrete and sharply outlined forms exist along an oval zone located asymmetrically relative to the geomagnetic pole-at night time at latitude f=67 ^o and during daytime at f=75 ^o - 77 ^o . Studies by Prof. Lebedinsky and his staff during the following years-and by his pupils after his death- revealed a close connection of the asymmetrical circle of the polar lights (called "polar oval") and the large-scale structure of the geomagnetic field with the fluxes of high-energy electrons within the magnetosphere.

Observations of the relative positions of electron and proton aurora, combined with camera data, made it possible to explain aurora polaris by a mechanism of direct excitation of the molecules and atoms of the earth atmosphere caused by the particles entering it. In future, data on aurora polaris obtained by Prof. Ignatyev will be an important aid for many students of the phenomenon.

In 1953 Alexander Lebedinsky took the post of professor of the Physics Department of the Moscow State University and moved to the Russian capital. Until 1958 he belonged to the Department of Geophysics and later moved to the Chair of Cosmic Rays of the Department of Nuclear Physics where he lectured on the astrophysics of cosmic rays and was actively engaged in space research. In 1959 he was on the staff of the Moscow University Department of Nuclear Physics (together with future academicians - A. Chudakov and S. Vernov) who were the first to explain the likely mechanisms of the formation of the newly discovered "terrestrial corpuscular emission" which became later known as the radiation belts of the Earth ^* . They formulated the hypothesis and conducted preliminary calculations of the generation of high-energy protons in the inner radiation belt due to the decay of albedo neutrons produced by cosmic rays during their interaction with the upper atmosphere of the Earth. This point of view has since become commonly accepted.

Ever since the launchings of the first artificial earth satellites in the 1960s, Prof. Lebedinsky focused his attention on studies beyond the earth atmosphere. It was in this field that he was looking for the explanations of many problems which had preoccupied him before, because it became possible to carry out geophysical and astrophysical studies across the whole spectrum of electromagnetic emissions unrestricted by the conditions on the earth surface.

It should be noted that in the ultraviolet band of the spectrum of the earth atmosphere absorbs emissions with wavelength of less than = 295 nm, and in the infrared one these emissions can pass through relatively narrow "windows of transparency" depending on the state of the atmosphere. Extending optical measurements beyond the confines of the visible part of the spectrum increases substantially the volume of information carried by electromagnetic emissions of the heavenly bodies and the Earth. In 1959 Prof. Lebedinsky was appointed research director of the Radiations Lab of NIIYaF of the Moscow University. And all of his further activities were associated with that appointment.

He regarded as especially attractive the prospects of studies of planets with the help of unmanned space probes

^* See: M. Panasyuk, "Breakthrough in Space", Science in Russia, No. 4, 2000. - Ed.

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(USP). It should be remembered, however, that launching studies of that kind represents a challenging scientific and technical problem. The first interplanetary flights-practically for testing various systems and components-had but few chances of success. It took years of hard work from the first mission to Venus (VENERA-1, 1961) and to getting data on venusian atmosphere from the VENERA-4 probe in 1967. Things were no better with flights to Mars: the failure of MARS-1 in 1962 and the first success of MARS-2, and MARS-3 in 1971. Under the guidance of Prof. Lebedinsky interesting experiments were planned from the start even for the first probes - VENERA-1 and MARS-1.

According to notions which prevailed before the 1960s, the surface of Venus could be one big ocean. A special instrument (of only half a kilo) made it possible to determine upon landing not only the aggregate (solid or liquid) condition of the planet's surface, but also the amplitude and period of the surface waves and the level of y-activity.

It was back in the 1950s when Prof. Lebedinsky put forward his hypothesis about water on the Red Planet contained in the surface strata in the form of permafrost. That was essential for solving the puzzle of life on Mars. As we know, all living organisms consist of organic molecules which can be identified by hydrocarbon bands in infrared spectra of surface reflections. By observations from the Earth in 1956 - 1958 the American astronomer Prof. V. Synton identified spectral reflections of dark regions of Mars which change with the time of the year, infrared absorption bands in wavelengths from 3.4 to 3.7 mcm. For confirming these observations researchers headed by Prof. Lebedinsky designed and built an on-board spectrophotometer for MARS-1.

One of the authors of this article, Prof. V. Tulupov, recalls that in the autumn of 1962, before the launch of MARS-1 the team headed by Prof. Lebedinsky travelled by car over hundreds of kilometers across the Kazakhstan steppes around the Baikonur launch site, registering the spectra of different sections of the surface with the help of a spectrophotometer. The data thus obtained was processed in the evening. Unfortunately, these studies could not be completed because of problems with VENERA-1 and MARS-1. Later on direct measurements on VENERA-4 (1967) confirmed atmospheric temperature assessments by radio observations (= 700 K) as mling out liquid water on the planet's surface.

The tempestuous progress of space technology made it possible to use purely biological means for the verification of the hypothesis about life on Mars. As we all know now only primitive life forms can exist on Mars and the presence of water there is a firmly established fact ^*.

The 1960s saw intense studies of the lunar surface by unmanned probes, and Prof. Lebedinsky took an active part in staging the first such experiments and in the interpretation of their results. He took part in the processing of the first circular panoramas of lunar surface obtained by LUNA-9 and LUNA-13 which made soft landings in 1966. The scientists also singled out and described the main types of fine surface structures on an area of some 50 m ² as visible on the panoramas. Spectral characteristics of the lunar surface in the ultraviolet and infrared bands were investigated by instruments supplied by the lab of Prof. Lebedinsky from board of the

^* See: I. Mitrofanov, "Solving Martian Mysteries", Science in Russia, No. 6, 2002. - Ed .

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unmanned probes ZOND-3 (1965), and LUNA-10, LUNA-12 and LUNA-13 (1966). The scientists measured the albedo, levels of emissions, and radiation temperature of the continental areas of the Moon and obtained data on microdiscontinuities on its surface. These findings retain their importance even after the manned landing on the Moon.

The lab of Prof. Lebedinsky prepared a number of experiments which were accomplished with the help of space probes. Some of these, conceived by the scientist, were carried out by his associates already after his death. These included measurements of the UV spectra of different classes of stars by probes KOSMOS-92, 121 and 224 in the wave range of 200 - 400 nm with the resolution of = 7 nm (because of high temperature, most energy of these stars should be emitted within that range). But the first such experiments staged by US scientists shortly before registered a sharp drop of glow intensity at l < 250 nm. This called for a radical reappraisal of the processes occurring in hot stars. But the first American conclusions were proved erroneous by experiments with KOSMOS probes. These observations can be regarded as the birth of our extra-atmospheric stellar astronomy.

From 1964 to 1967 researchers (of NIIYaF Institute of Moscow State University) carried out a large volume of studies of the atmosphere of the Earth using nine satellites of the KOSMOS series. And it should be pointed out that geophysical measurements from such probes offer considerable advantages over ground studies. They make it possible, within a short span of time and using instruments of the same type located in many regions of our planet, to study latitudinal, daily, local and seasonal variations of this or that phenomenon within a broad band of electromagnetic emissions. This data is of particular importance as collected from vast areas of the oceans, polar regions, desert and mountainous regions which occupy nearly 80 percent of the earth surface. Such ground observations are either absent or are few and far between.

The KOSMOS-45, 65 and 92 probes were used for filter observations of night-sky glow initiated by Prof. Lebedinsky. Simultaneously with the Americans, our researchers registered its sharp decline at l < 250 nm. Studying the daily-latitudinal variations of glow of molecular atmospheric oxygen in the range of 250 - 315 nm, they discovered the absence of longitudinal dependence of the process in the range of +/-50 ^o latitude. Measurements were also conducted of the spectra of reflection by the earth atmosphere of solar radiation in the ultraviolet band (220 - 330 nm) at the resolution of 1.5 nm. The data were later used for studies of characteristics of reflected emissions and global ozone distribution. These experiments went 4 years ahead of similar studies in the West.

The time of conduct of the above experiments coincided with the birth of satellite meteorology. At that time there were no METEOR probes and there were first attempts to use satellite data. Prof. Lebedinsky joined these experiments with his typical zeal and the staff of the GIDROMETsSENTR were also involved. They conducted, among other things, comparisons of the spectra of outgoing emissions as measured from satellites, with ground observations of the same time and location and also calculations of emissions in different bands of the spectrum.

Even some relatively brief look at these experiments and their results demonstrates the range of interests of Prof. Lebedinsky. He was always surrounded by young scientists and shared his experience and knowledge with them. Discussions of new results took place at his apartment and went on until late at night. People who knew him personally could not imagine him at rest even for a short while. His motto was constant, purposeful and enthusiastic movement forward.

The range of activities of Prof. Lebedinsky was not confined to the walls of his institute. He devoted much time and attention to the promotion of geophysical research in the associated centers, often delivering lectures and reports on topical aspects of space research and studies of the upper atmosphere. He was an active participant in international meetings and conferences and was a member of the International Union of Astronomy, International Union of Geodesy and Geophysics, Committee on Aurora Borealis, the International Association of Geomagnetism and Aeronomics and member of the editorial board of the Planetary and Space Science magazine.

A demanding and strict person, Prof. Alexander Lebedinsky was noted at the same time for his extraordinary benevolence and responsive attitude to people around him. Many of his friends and acquaintances gratefully remember his readiness to help others and render them material and/or moral support.

Prof. Lebedinsky died in a tragedy on September 9, 1967 in the prime of his life. He lived a short, but wonderful life which was totally devoted to the service of science and people.

His memory was honored at a special session of the American Astronomical Society. Speech on the occasion delivered by a prominent space scientist, Prof. Fred Singer was published in 1968 in the journal of Astronautics and Aeronautics . He said that people who knew Prof. Lebedisky were involved into his work because he was able to pass on to them the interest in his studies. Talking with him one always felt the excitement from having a new result or a new hypothesis... Over a number of years discussions with Prof. Lebedinsky on any subject in space physics were always stimulating and intellectual events. He brimmed with new ideas, hypotheses and critical observations... The works of Alexander Lebedinsky had a tremendous impact upon international studies of space. He was a modest and benevolent colleague and he will be missed by many; probably, most of all by his pupils...

Illustrations supplied by the authors

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