Achievements of astronomy have been in the focus of public attention for centuries. Today this interest is reflected in numerous scientific publications, like the one that has appeared in the popular science magazine PRIRODA (Nature). Its author is Vladimir Reshetnikov, Dr. Sc. (Phys. & Math.) of the St. Petersburg State University. Summing up the progress and achievements of astronomical research over the past few decades, and quoting the opinion of our leading expert in the field Acad. Vitally Ginzburg, the author of the article points out that research tasks in this field (which are changing with time) form what he calls a certain "physical minimum" which every researcher should be familiar with.

This covers the general theory of relativity and its experimental verification; gravitational waves and their detection. Also involved are problems of relations between cosmology and high-energy physics; neutron stars and pulsars; supernova and black holes; quasars and galactic nuclei; dark matter (hidden mass) and its detection; super-high energy cosmic rays and their origin; gamma-bursts and hyper- nova, neutrino in physics and astronomy, neutrino oscillations, etc.

As Dr. Reshetnikov points out, these areas of research are of primary importance and are of a fundamental nature. However, they reflect, above all, the physicist's view of the astronomy. And although it is rather difficult to identify the difference in the views on the above problems of "specialists in celestial matters", this difference does exist. It probably consists in the relatively greater attention of the latter to the objects of research as such (stars, galaxies, gas nebulae, etc.), and not just to the physical processes therein. What is more, an astronomer can visualize, better than a physicist, the authenticity of the figures and assessment accrued from observations.

The aforesaid problems were the subject of thorough discussions at the 1997 international conference on the Canary Islands. The range of subjects in the presentations covered all areas of modern astronomy-the Universe at Large.

The Conference was opened by the prominent American expert in the field Prof. A. Sandidge. His name is linked with a range of major achievements of observation cosmology, with the development of the current notions about the formation and evolution of stars and galaxies and with the modern school of distance measurements across the Universe. The scientist formulated a total of 23 problems which will probably be resolved over the next 30 years. These were divided into three sections- those concerning the general properties of galaxies, of the Milky Way and observation cosmology.

The first of these sections, or areas of research, deals with morphological classification put forward back in the 1920s by the famous American astronomer, Prof. Edwin Hubble, which divides galaxies into elliptical and spiral ones. This approach, linked with their shape, rests on how galaxies look in the optical band. As was later established, however, their "external appearance" reflects a range of physical parameters-mass, luminosity, the amounts of atomic, or nascent, and molecular gas, dust, type of stellar "population", the rate of birth of stars, etc.

The author of the PRIRODA article does not go into a detailed analysis of the problems put forward by the American scientist, but sums them up into one basic fundamental question: how the biggest galaxies around us were formed? It was originally thought that they were born at the early stages of the evolution of the Universe. But later scientists changed their views, which led to an alternative scenario: galaxies originated in the process of evolution and their interaction with the environment (inter-galactic space and other galaxies) was developing in parallel. Some of the recently discovered facts add considerably weight to this approach. It has turned out, for example, that the share of interacting galaxies is rapidly increasing with the growth of the red shift, that is when considering the earlier stages in the evolution of the Universe. Thus, when it was twice "younger", from one third to one half of all galaxies must have been in a state of strong external gravitational disturbance or in the process of merging with their kind. Thus it is obvious that such

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Hubble succession of galaxies.

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interactions and mergers had an important part to play in the formation of galaxies ^* .

The second group of problems, put forward by the American scientist and discussed by the author of the article, deal with the problems of the structure and origin of the Milky Way. What we are dealing with here are more concrete things because we are inside our stellar system which is much more accessible to examination in details (at least the space close to the Sun). It is therefore not accidental that considerable progress has been made over the past few years in studies of the Milky Way with the help of space probes. The HIPPARCOS observatory, for example, has made it possible to measure the distance to hundreds of thousands of stars within several hundreds of parsecs from the luminary. As a result the structure of the nearest surroundings of our Galaxy has become much clearer. Observations in the information band with the help of the COBE satellite made it possible to form for the first time the general picture of the Milky Way. It turned out, for example, that the central part of the Galaxy is nothing but an elongated structure with its main axis "stretched out" towards the Sun.

Achievements have also been made with the help of ground observations. Thus, investigating stars of the outer areas of the bulge (central stellar accretion) a team of British astronomers discovered in 1994 a dwarf galaxy located practically within the limits of the Milky Way at a distance of 16 kpc from its center. It is strongly deformed by tidal disturbance of the Universe and stretches out like a giant arc almost perpendicular to its plane. And one can also think about the Large and Small Magellanic Clouds, about the giant gas tail which connects them with our stellar system (Magellanic Cloud) and we obtain a clear picture of the ongoing process of "construction" of the Milky Way.

The third group of problems posed by Prof. Sandidge before astronomers, which are also examined in this article, concerns problems of expansion of the Universe, the evolution of formation of the original galaxies, the development of a scale of distances towards them, the determination of the composition and origin of the intergalactic medium, etc.

At the end of his publication, Dr. Reshetnikov points out that the current stage of the astronomical science can be compared with the 1920s (discoveries of galaxies, expansion of the Universe) or with the 1960s (discovery of quasars, pulsars, relict radiation). The general picture of heavenly space is changing and we can now observe directly for the first time galaxies from the epoch of their formation and up to the present, planets of other stars are being discovered.

The author of the article concludes by saying that astronomical studies are far from being completed. The range of puzzling and exciting problems before the "astrologers" of today looks really endless!

"Astronomical Problems of the Start of the 21st Century, or 23 Problems of Sandidge" (in Russian), V. Reshetnikov, PRIRODA, No. 2, 2003

Prepared by Yaroslav RENKAS

^* See: A. Marakushev, "Solar System and Its Stellar Analogues", Science in Russia, No. 5, 2001. -Ed.

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