The Zenith-telescope Bought: 1895 Company: Repsold and Sons, Hamburg

The observer’s position depending on the telescope’s position has in all times been one of the biggest inconveniences in organizing observations. The uncomfortable position of the observer causes muscle tension for him which is accompanied by incorrect determination of the position of the object. It is especially uncomfortable to observe when the object is located very high in the sky, i.e. near the zenith.

One of the possible solutions is to fasten the ocular to the edge of the telescope’s revolving axis. Inside the axis there is an opening where light is directed with the slanting mirror or a prism. If such a telescope has the azimuthal mounting, one of the axes (the axis of zenith distance) is always parallel to the surface of the Earth and the ocular at its edge is on one and the same height. Naturally it was impossible in the case of such telescopes to use the clock mechanism. One of the positive qualities of the system was, in addition to the above mentioned quality, easy transportation, simple placement and the ability to light the field of view with the help of a light source (lamp, candle) put to the other end.

The Repsold zenith-telescope was purchased by the then director Grigori Levitski in 1895. For the relatively small observation instrument (the diameter of the objective is 7 cm) a separately located pavilion with a revolving dome was built. The data about the use of the instrument is missing. The only printed work is Erich Schoenberg’s study about the oscillation of Tartu’s degree of latitude in the years 1905–1909. The exact establishment of the astronomical degree of latitude became the main application of the zenith-telescopes.