The Zeiss Refractor Bought: 1911 Company: Zeiss, Jena

The Tartu Zeiss refractor was ordered in connection with the one hundredth anniversary of Tartu University, newly opened in 1802. It was even planned to build a new observatory but this project was not financed. At first they planned to restore the Fraunhofer refractor, updating its design and replacing worn-out parts. The work was more expensive than expected and as for the same money Zeiss agreed to make a new telescope (although somewhat smaller). It was decided to buy the new one. The telescope was assembled in 1911. Regular observations started in the winter of 1912.

The Tartu Zeiss telescope is the child of the age of machinery. Reliability and convenience in use has made “the ethics” – the oak body and brass details – less important being replaced by cast iron and milled steel. The telescope was supplied with a perfect set of additional details: beside the Petzval camera there was a set of oculars fastened to the revolving turrel (seven oculars, magnification 60–720 times), the ocular micrometer with five oculars (magnification 120–500 times), filters, photometrical wedge, and the zenith and sun prism.

ObservationsThe telescope did not bring along a new turn in the development of the observatory. Astronomy had entered a new photographic era and visual observation had no earlier importance. Fortunately the astrograph made at the Zeiss company belonged to the telescope and from the years 1912–1914 there is data about the results of photographic observations of mainly planets, comets and asteroids.

In 1914 World War 1 broke out and the front quickly reached Estonia. In 1915 it was decided to evacuate the university. The Zeiss telescope also belonged to the equipment taken to Tomsk in Russia. It was given back in 1921. The variation of the brightness of the Neptune for determining its rotation period (Öpik and Livländer, 1922–1923) was studied.

In 1924 a radical decision from the point of view of observational astronomy was made: The astrograph was separated from the telescope. In 1927 the Zeiss telescope was freed from the role of the astrograph’s guide and again the telescope could be used for traditional observations: they observed binary stars (Öpik 1924–1930, Riives 1938-1940), planets, asteroids and comets – the asteroid Eros (Kipper 1931), the crossing of the planet Mercury over the disc of the Sun (Öpik and Livländer 1924), the eclipse of the Jupiter`s satellites (Muischneek 1932), the occultation of stars (1923 and 1932). The method of determining the declination of zenith stars with the help of the mercury horizon (Kipper and Livländer 1932–1934). These observations were also continued during the Soviet period when the Tartu observatory was handed over to the Academy of Sciences in 1947.

Together with other reconstructions important improvements of the Zeiss telescope were made. A bad original objective was replaced by the trophy objective of the same diameter; the focus distance was 3 m instead of the former 3.6 m. In 1950 the two photo cameras were fastened to the telescope allowing to photograph the area of the sky being observed in two spectral regions at the same time. The system was used in observing asteroids and in the patrol observations of the variable star ε Aur. The last scientific research made by the telescope was the photometric observation of Nova Herculi in 1960.

The new life of the Zeiss telescope. The telescope was renovated in 1994. From that time onwards its main function is in acquainting the people of Tartu with the starry sky and in observing planets. In 1996 the established non-profit organization – the Astronomy Club of the old Tartu Observatory began to manage the astronomical part of the old observatory. During the last fifteen years the observation register has been signed by more than ten thousand people.