The Astronomical Observatory in Cluj was built between 1921 and 1934 on the site of today's "Sigma Center" (the name of the Observatory street was given precisely by the Astronomical Observatory, which functioned here until 1977, when it was demolished and on its site was built the "Electrosigma" industrial assembly). The initiative for creating the observatory belonged to Mathematics teacher George Bratu, dean and vice-dean of the Faculty of Sciences, director of the Observatory in Cluj between 1919-1920 and 1928-1941.
The first specialized scientific instruments: a Newtonian reflector telescope (50 cm mirror diameter), a Prin equatorial telescope (20 cm lens) and many books on astronomy were commissioned through the efforts of Professor George Bratu and Professor George Demetrescu (director of the Observatory between 1921-1928). Since 1982 the Observatory operates in a new building located in the south side of the "Alexandru Borza" Botanical Garden.
The material base purchased in 1982 consisted of: a Coudé-Zeiss refractor (150/2250) (located in the 600 cm Gautier-Prin dome), a Zeiss refractor (100/1000), a Zeiss sextant and a Zeiss theodolite. These tools were added to those already existing from the interwar period, which acquired heritage value in the meanwhile (the Newtonian telescope and the Prin telescope, mentioned above). In the 80s the Observatory was equipped with: 130 mm Reinfelder refractor, 15 cm "Vierlinser" astrograph (quadri-lenticular lens), 70 mm Frauhoffer refractor, a "lunette de passage" (for observing the celestial bodies crossing the local meridian) and a universal instrument (theodolite).
Since 2007, in a mixed financial effort (of the Romanian Government and of UBB) the material assets of the Observatory included the purchase and installation of a new 450 cm dome (PD 15 Technical Inovations), which houses a 30 cm Meade Schmidt-Cassegrain catadioptric refractor and a Coronado solar refractor with 60 mm Hα bandwidth filter. Other purchases included: a SBIG spectrograph, CCD cameras of various types, a 26 cm Vixen reflector telescope installed in parallel with the Coude instrument in the old dome, telescope accessories, and a network of 15 Dell computers.
The Observatory benefits from a specialized library, which contains over 16,000 titles and is open Monday to Friday from 9.00 to 15.00.
The Astronomical Observatory is an institution of education and research in areas such as general astronomy, astrophysics, celestial mechanics, artificial satellites. The astronomy classes are open to students of the Faculty of Mathematics and Computer Science and of the Faculty of Physics. The fundamental elements and specific elements are learned on the spot, where students participate in courses, seminars and laboratories. The activity within the Observatory is reflected by the research seminars on the topic of "Celestial mechanics and space research" and "Structure and evolution of stars" in the articles and books published, as well as in national and international workshops organized.
Since 2008 the Observatory organizes activities for the general public also. Visitors are welcome every Friday night, after dark, for a program scheduled for 2 hours. It consists of an introduction (projecting a simulated configuration of the sky map of the moment accompanied by an explanation of the celestial objects that will be observed), and a practical, observational part, using the existing instruments.