The Jastrzębowski Boulder
The sundial located on the escarpment near the Old Orangery building. It has been placed on an uneven surface of a granite boulder (glacial erratic). The monumental piece of rock brought by a glacier was found when then Botanical Garden was established. It is most likely the oldest protected glacial erratic in Warsaw.
The sundial was made by Wojciech Jastrzębowski (1799–1882), a Professor of the Marymont Institute of Agriculture and Forestry. In 1828, he carved out hour lines, date lines, and indicators of the mean solar time on the surface of the stone. He embedded in it an iron gnomon with protrusions, pointing towards the Earth’s celestial pole.
The sundial was used not only to show the time. It also helped locate celestial spheres. It was made with the help of an instrument invented by Professor Jastrzębowski, known as the “Jastrzębowski Compass” or the “Polish Compass”. The location of the sundial was chosen because of the vicinity to the Astronomical Observatory. Established in 1825, it is situated within the area of the contemporary Botanical Garden.