{ Laurits Leedjärv 2004 }

Astronomy [in Estonia]

The starry night sky has fascinated people since time immemorial. Present-day astronomers in Estonia try to understand the structure and evolution of the vast Universe as a whole, and to uncover the most intimate secrets of the stars. About 25 highly qualified astronomers is rather a large number given the small size of Estonia. It is therefore tempting to say that the love that ancient Estonians had for the starry sky has, through time, been transformed into a highly developed form of professional astronomy.

However, a deeper look at the roots of astronomy also reveals the irrefutable role of the University of Tartu and, in particular, that of the prominent astronomers who worked there. The old University Observatory, built at the beginning of the 19th century, began to gain worldwide renown under the directorship of Friedrich Georg Wilhelm Struve.

On several occasions, pioneering work by Tartu astronomers has significantly contributed to the comprehension of how large the Universe is, and how it functions. The story begins with Struve, who, in 1837, published the results of his efforts, stretching over many years, to measure the distance to the bright star of Vega. He concluded, that the light from Vega travels for 26 years to reach us. This was very close to the results, which have been achieved with modern precision measurements.

By the beginning of the 20th century, about 15,000 nebulae were known to astronomers. But nobody knew how far away they were. Ernst Julius Öpik, the Grand Old Man of modern Estonian astronomy, invented a novel method for estimating the distance to nebulae. And when applying this method to the great Andromeda nebula, conclusively demonstrated that it lies well outside our own Milky Way, forming an independent “island” in the Universe. Once again, the estimated size of the Universe increased several thousand fold.

After World War II, Aksel Kipper initiated the building a new observatory at Tõravere, about 20 km south-west of Tartu. This was opened in 1964, and has since then catered to the needs of both astronomers and atmospheric scientists. In 1975, the observatory obtained a 1.5 metre reflector telescope, which is the largest optical telescope in Northern Europe.

The spirit of Struve and Öpik most prominently lives on in the studies carried out at present by Jaan Einasto and his colleagues. The highlights of their research, during the last 30 years, include the discovery of dark matter, of the cellular structure of the Universe, and of the regularity of that structure. In the late 1960s and early 1970s, astronomers began to realise that most, if not all, galaxies are surrounded by coronae of invisible dark matter. And astronomers from Tartu were among the first to publish the results of their research concerning these massive galactic coronae. The paper by Jaan Einasto, Enn Saar, and Ants Kaasik in the prestigious journal “Nature”, in 1974, has remained one of the landmarks in the development of 20th century astronomy.

By now, it has become evident that ordinary visible matter forms only about 4 per cent of the energy density in the Universe. 23 per cent is the above-mentioned dark matter, and the remaining 73 per cent is, so called, dark energy, causing the eternal expansion of the Universe. This dark power has shaped the structure of the Universe from the very start, causing the presently observable regularity of the structure. And again, Tartu astronomers, led by Jaan Einasto, have been at the forefront of these studies. Their paper in "Nature", in 1997, was among the first to describe the Universe as an almost regular cellular structure. In other words, long chains of clusters and superclusters of galaxies form a three-dimensional net with a characteristic length of about 400 million light years and with huge voids inside the interstices. Such a cosmic honeycomb must have had its origin in the course of the very first second after the Big Bang, which took place some 14 billion years ago. At present, our astronomers are involved in the preparations for the space mission Planck, which, after being launched in 2007, will map the remnant radiation from the Big Bang with unprecedented accuracy.

Studying the processes governing the lives of stars is another main research area for Estonian astronomers. Among our stellar specialists, there are the "classical" astronomers who make night-time telescopic observations, at least as much as the Estonian climate allows. The main objects of study are non-stable stars, which are variable on different time scales, mostly non-periodically and unpredictably. The most important prerequisite for understanding the nature of those stars is recording, for as long as possible, the series of the variations. At the same time, a theory of stellar atmospheres has been developed. And thereby, as a result of the co-operation between theoreticians and observers, a consistent picture of the nature and evolution of several types of stars is emerging at Tõravere.

Besides professional astronomers, there are always people looking into the skies as a hobby. Thousands of people, mostly schoolchildren, visit the observatories at Tõravere, Tartu, and Tallinn each year. And an all-Estonian conference of amateur astronomers is held on an annual basis. Perhaps these facts, together with the internationally recognised achievements of our professional astronomers, justify the claim, that there is something special in the Estonians’ relationship with the starry sky.