09_02 Furdui Et Al.
history of Astronomical Observatory Cluj
THE ROMANIAN ASTRONOMICAL OBSERVATORY OF CLUJ-NAPOCA: NINETIETH ANNIVERSARYVASILE POP 1, OVIDIU FURDUI 1, VASILE MIOC 2 Astronomical Institute of the Romanian Academy Astronomical Observatory Cluj-Napoca Str. Cireilor 19, 400487 Cluj-Napoca, Romania E-mail: firstname.lastname@example.org , email@example.com Astronomical Institute of the Romanian Academy Str. Cuitul de Argint 5, 040557 Bucharest, Romania E-mail: firstname.lastname@example.org 1Abstract. We present the history of the Cluj-Napoca Astronomical Observatory, from foundation to actual endowment and activity. We also survey the characteristic astronomical researches undertaken in this observatory, and the most significant persons who worked and work here. The paper is intended to emphasize the role of the Cluj-Napoca Astronomical Observatory in the Romanian astronomical life at its 90th anniversary. Key words: history of Astronomy astronomical observatories.1. HISTORY BEFORE 1919Interests in Astronomy in Transylvania have been known since ancient times. It is enough to mention the Dacian sanctuaries in Sarmizegetusa Regia (see Fig. 1), where some rock alignments were built in order to mark the Suns position at equinoxes and solstices, valuable data to develop the Dacian calendar. All over the world, both astronomical education and research is delivered or leaded by universities or science academies. The set up issue of the first Transylvanian university has the subscription on 12 May 1581, at Vilnius, by Stephan Bathory, who was King of Poland and Prince of Transylania. The University launched its work in Cluj in 1583 with Antonio Possevino as Rector, and was divided in three Colleges: Theology, Philosophpy and Law. The students studied in Latin, and were guided by Catholic monks. In 1585 there were more than 130 students; among them, it was Nicolae Ptrascu, the son of Michael the Brave (in Romanian: Mihai Viteazul), the Prince of Wallachia at that time. Michael the Brave, as the Prince of Wallachia, offered his protection to theRom. Astron. J., Vol.19, No. 2, p. 000-000, Bucharest, 2009Vasile POP, Ovidiu FURDUI, Vasile MIOC2University when he naturally annexed Transylvania (as a Romanian principality) to Wallachia, in 1599. Displaying a great interest in the scientific work of that time, some enlightened Catholic bishops, among others Janos Vitez (Bishop of Oradea between 14451465), with the support of Professor Georg Peurbach from the University of Vienna, built up a small astronomical observatory owned by the Church. At the end of the XVIII-th century, Ignatius Batthyani (17411798), the Catholic Bishop of Alba Iulia, managed to transform a church of the Trinitarian Order into a Library and Astronomical Observatory (see Fig. 1). In this context, Antonius Martonfi was sent to Vienna to study Astronomy with Maximilian Hell. After his return to Alba Iulia, he became the Director of this observatory (observatory that was in service from 1796 until 1860, when Martonfis canonical astronomer position was canceled). The astronomical institution was endowed with several specific observation instruments: a mobile quadrant, a meridian circle (within the acception of that time) of 74 cm diameter, as well as a refractor of 8.5 cm aperture and 125 cm focus. Other equipments consisted of three refractors having apertures of 3.5 cm, 5 cm, 9 cm, sidereal clocks, celestial spheres, all rendering high accuracy for those times. All these can be found in the inventory of Batthyaneum Library in Alba Iulia.Fig. 1 Left: the great Dacian sanctuary of Sarmizegetusa Regia. Right: the Batthyaneum Library and Observatory in Alba Iulia.In the year 1603, the Protestants abolished the Catholic university, and exiled the Jesuits out of Transylvania.Under the Habsburg domination, the Jesuits returned into Transylvania and founded Academia Societatis Jesu Claudiopolitana in 1698, with three colleges: Theology, Philosophpy, and Science (Mathematics and Natural Sciences). Mathematics courses were given by Ioan Fridvalszky and Maximillian Hell; the latter one became the Director of Vienna Astronomical Observatory. This Academy was closed in 1773.3The Astronomical Observatory of Cluj Napoca: 90th AnniversaryThe Piaristic Academic College was founded in 1776 and the course of Mathematics and Elements of Astronomy was given by Professor Adolf Geg. Among others, Gheorghe Lazr, the future founder of schools in Wallachia, was student here. At this time, a room with small astronomical instruments was opened in the tower of the College. It seems it was the first attempt to launch an astronomical observatory in ClujNapoca. The language of instruction was Latin until 1848, when the Hungarian language was imposed as official language of the college. During the Austro-Hungarian dualism, the proper political context emerged in the decision of the Hungarian Parliament, in 1872, to create a Hungarian University in Cluj, with Aron Berde as its first Rector. At its beginnings, the university, covered four sections: law and political sciences, medicine, philosophy (languages and history), and mathematics and natural sciences. There were then enrolled 285 students, but only 15 of them had Romanian origin. The Faculty of Mathematics and Natural Sciences did not have either an astronomical observatory or astronomical instruments for training programmes. It is not interestless to point out the fact that the renowned journal Astronomische Nachrichten (AN) revealed that Friedrich Wilhelm Schwab, from Klausenburg (Cluj) University, observed variable stars and published his results. He suspected some observed stars to be variable ( Pegasi and Pegasi), observed Mira Ceti, Aquilae, Nova Persei, and discovered a new variable star (U Sagittae). All this was published in the AN between 1878 and 1901. He also took part in a German expedition for Venus transit (1882), at Punta Arenas, and studied the comet 1882 II. Schwab was the first person who regularly performed variable star observations in Transylvania.2. THE ROMANIAN UNIVERSITY OF CLUJ CREATED HIS OWN ASTRONOMICAL OBSERVATORY: PAST AND PRESENTThe Transylvanians natural desire of owning a national higher-education institution became reality in 1919, when the Romanian University was founded in ClujNapoca. In the first semester of the academic year 19191920, the university enrolled 1871 students. The first team of exceptional professors made the Upper Dacia University one of the most important sources of Romanian culture. In October 30, the university changed its name into the King Ferdinand I University, to glorify the name of the unifier of Great Romania. The Mathematics section within the Faculty of Sciences has been founded by Dimitrie Pompeiu, Gheorghe Bratu, Aurel Anghelescu, Nicolae Abramescu, Gheorghe Iuga, Theodor Anghelu, Petre Sergescu. The name of Professor Gheorghe Bratu (18811941), see Fig. 2, is essentially associated to the beginnings of the astronomical research and education at the UniversityVasile POP, Ovidiu FURDUI, Vasile MIOC4of Cluj-Napoca. He was born in Bucharest, in a family originating from Braov. As soon as he graduated the high school and the Faculty of Sciences of Jassy, he was awarded a scolarship in Astronomy at the renowned university Sorbonne (1908), which he successfully completed. Upon this and between 19091912, he became probation astronomer at Observatoire de Paris. Professor Bratu got his Ph.D. in Mathematics in 1914 with a thesis dedicated to calculus applications in mechanics problems, under the supervision of Paul Appell, then returned to University of Jassy, where he worked as assistant professor (19141918). In 1918 he was promoted as associate professor of Calculus and next year became Professor in the University of Cluj-Napoca, also giving courses within the Astronomy department of this University. In early days at Cluj-Napoca, on 10 December 1919, Professor Gheorghe Bratu submitted a request for the setting up of the Astronomical Observatory of the town, approved by the Senate of the University on 1 October 1920. Between 19221928, Gheorghe Demetrescu (18851969), see Fig. 2, Professor of Astronomy at the University of Cluj-Napoca worked along with Professor Bratu in the development of the observatory building plans and in funding the building works. The site for this unit was donated by the Town Hall in 1925 at the southern border of the town, while the University ordered the following tools from Gillon Company in Paris: a Prin refractor, with aperture of 20 cm and focal length of 300 cm; a Newton reflecting telescope with a parabolic mirror of 50 cm diameter and 250 cm focal length; the 6 m diameter dome as tool shelter. The buildings of the Observatory in 1950 (including the main building with the library, the astrophysics building with the dome, the meridian hall), as well as the main instruments, are presented in Fig. 3 below.Fig. 2 Left: Professor Gheorghe Bratu (18811941). Right: Academician Gheorghe Demetrescu (18851969)5The Astronomical Observatory of Cluj Napoca: 90th AnniversaryFig. 3 Left: the buildings of the Astronomical Observatory of Cluj-Napoca in 1950. Right: the Newton reflector and the Prin refractor.In 1927, the meridian hall was built, and in 1929 the Timing Service was organized, broadcasting time data to all the institutions in the town and replacing the Firemen Time Service. The library, the directors house and the teaching halls were also built then. After Professor Gheorghe Demetrescu was appointed, in 1928, as Astronomer and Deputy Director of the Astronomical Observatory of Bucharest, Professor Gheorghe Bratu gave up on his position in the Calculus Chair, becoming both the Chairman of the Astronomy department and the Director of the Astronomical Observatory. Deprived of the funds needed for the foreign experts payment, ProfessorGheorghe Bratu managed to attract his son into the project of mounting the major tools inside the dome.Beginning with 1938, the Astronomical Observatory of Cluj-Napoca became operational, that meaning, it could start its own astronomic research. Among the first graduates in Mathematics from the University of Cluj-Napoca (1924), Professor Bratu kept Ioan Curea (19011977) and Ioan Armeanca (19001954) as observatory staff. Later on, Ioan Armeanca, was sent to the University of Gttingen, Germany, for Ph.D. studies. In 1939 Ioan Curea completed the implementation of a seismic observation station in ClujNapoca, while Ioan Armeanca attached the Guthnick, a state-of-art photoelectric photometer (for that epoch all over the world), to the Newton reflector telescope, acquired from his German mentor. Following the Vienna Diktat, in September 1940, in only four days, all the equipment was dismounted into pieces, packed and sent to Turda, Aiud, then to Timioara. The astronomers Ioan Armeanca, tefan Radu, and Gheorghe Chi were sent to the war front (fortunately, they came back). Professor Gheorghe Bratu, who was, at that time, also the Dean of the Faculty of Sciences in Cluj-Napoca, in the middle of those terrible events, suffered a stroke and passed away on 1 September 1941. He was burried in Jassy. After this, Constantin Prvulescu (18901945) became Professor of AstronomyVasile POP, Ovidiu FURDUI, Vasile MIOC6and Director of the Astronomical Observatory of Cluj-Napoca (see Fig. 4). Since 1945, the equipment was dispatched back to Cluj and its reinstallation started under the supervision of Professor Ioan Armeanca (19001954), Director of the Observatory between 1945 and 1954 (see Fig. 4).Fig. 4 Left: Professor Constantin Prvulescu (18901945). Right: Professor Ioan Armeanca (19001954).Fig. 5 Left: Professor Gheorghe Chi (19131981). Right: Professor Arpad Pal (19292006).In 1951, the Astronomical Observatory was transferred from the University to the Cluj Branch of the Romanian Academy and became one of its research institutes. Along7The Astronomical Observatory of Cluj Napoca: 90th Anniversarythis period young scientists were also employed as research staff (Ioan Todoran, Elvira Botez, Ioan Popa). During the same period, Professor Ioan Armeanca restored the photographic photometry laboratory, purchased a Reinfelder-Hertel refracting telescope with 13 cm aperture and 140 cm focal length, as well as a Graff visual photometer with optical wedge. In 1961, the Astronomical Observatory rejoined the University of Cluj. Between 1954 and 1977, the Director of the Astronomical Observatory was Professor Gheorghe Chi (see Fig. 5 above). He has begun his work in the Observatory on 1 February 1936. At the time when the cosmic era began, era marked by the launch of the first artificial Earth satellite, Sputnik-1, in 1957, Professor Gheorghe Chi did his best to acquire the instruments and accessories needed for satellite tracking: small AT refractors, a chronograph, a printing theodolite, a radio receiver for time signal calibration, a UFISZ-25-2 photographic camera for artificial satellite observation. Professor Gheorghe Chi also started the photoelectric photometry researches. The astronomers Ioan Todoran, Vasile Ureche and Vasile Pop developed with their own efforts the first modern photoelectric photometer, which was attached to the 50 cm Newton telescope. In this configuration, the tool performed thousands of observations. In 1976, the city expansion caused bad observing conditions, which forced the Observatory relocation 8 km South on Feleacu hill, at 750 m altitude (see Fig. 6 below). Professor Gheorghe Chi, assisted by Vasile Pop, chose the site and geographic location for the new building and developed its plans. Since 1977, after Professor Gheorghe Chi retired, Professor Arpad Pal (1929 2006) (see Fig. 5 above) became the Director of the Astronomical Observatory until 1992. From 1977, the Feleacu observing station was owned by the Centre for Astronomy and Space Sciences (CASS) from Bucharest (currently the Astronomical Institute of the Romanian Academy).Fig. 6 Feleacu Observing Station in 1985.Vasile POP, Ovidiu FURDUI, Vasile MIOC8In 1978, the old buildings of the observatory (built by Professor Gheorghe Bratu) were demolished, and a new observatory was erected in the southern part of the Botanical Garden. Meanwhile, Dr. Vasile Pop was responsible with the acquisition of new equipment from Carl Zeiss Company, Germany: a Coud refractor (150/2250 mm), a Zeiss refractor (100/1000 mm), theodolite, sextant, all of them obtained in 1980, using a special investment funded by the University. The new observatory building was finished in 1982 and includes: the dome (6 m diameter), the meridian hall, observation processing laboratories, the library with more than 20,000 entries, classroom and appendix. Between 1992 and 2000, Professor Vasile Ureche (born 1934) was the Chairman and Director of the Astronomical Observatory. Specific logistics for all work was fixed during the research projects this time. In 1995, the Cluj Branch of the Romanian Academy purchased a Meade reflecting telescope of the type Schmidt-Cassegrain (LX 200, 40/406 cm), endowed with a CCD camera, installed on Feleacu observing station in place of the elder Newtonian telescope. This new device provides the best results for astrophysical observations performed in Romania. The two main instruments of the Cluj-Napoca Observatory (the Coud refractor and the Meade reflector) are presented in Fig. 7.Fig. 7 Left: the Coud refractor. Right: the Meade reflector.9The Astronomical Observatory of Cluj Napoca: 90th AnniversaryBetween 2000 and 2005, Professor Vasile Pop (born 1940) became the Chairman and Director of the Astronomical Observatory. In 2001, a GPS receiver was installed in the Astronomical Observatory of the University, while in 2004 a new CCD camera was acquired and installed to the Coud refractor. All this logistics was deployed for education and astronomical researches in both Babe-Bolyai University of Cluj-Napoca and Cluj Branch of the Romanian Academy. Since 2005, Associate Professor Ferenc Szenkovits has been appointed the Chairman of the Astronomy and Mechanics department, and also the Director of the Observatory.Fig. 8 The Observatory with the second dome.In 2006, a Ritchey-Chrtien reflector (Meade 12 RCX400, having 30.5 cm diameter and 244 cm focus) was purchased by the Cluj Napoca Branch of the Romanian Academy, and fitted in the Feleacu Observing Station. A similar telescope was purchased by the University in 2007 and fitted in a new ProDome PD-15, with a diameter of 4.5 m (see Fig. 8 above), at the University Observatory in the Botanical Garden.3. RESEARCH DONE AT THE ASTRONOMICAL OBSERVATORY OF CLUJ-NAPOCAThe necessary logistics of the Astronomical Observatory was near the purpose fulness at the end of 1938 year, at the time when the Observatory was managed byVasile POP, Ovidiu FURDUI, Vasile MIOC10Professor Gheorghe Bratu, and the research was organized in three research units: cooperation at The 20th Centurys Skies Photographic Map Catalogue (Gheorghe Bratu, Ioan Armeanca, Gheorghe Chi, tefan. Radu), the photometric study of variable stars (Ioan Armeanca, Gheorghe Chi, tefan Radu), and the study of earthquakes in Transylvania (Ioan Curea). As probation astronomer of the Observatoire de Paris (19091912), Gheorghe Bratu has determined ephemerides of small planets (1911), ephemerides for lunar and solar eclipses (1912), and had an important contribution to the Catalogue of Fundamental Stars (1910). In drawing out the monumental work of The 20th Centurys Skies Photographic Map Catalogue, recorded on copper plates and supervised by Observatoire de Paris, the task of the Astronomical Observatory of Cluj Napoca was to determine the coordinates of the stars around the +20 declination zone. This operation was achieved between 1933 and 1947, and the results were published in Paris in 1950 (Publications de l'Observatoire de Paris). Professor Gheorghe Bratu also obtained noticeable results in the domains of nonlinear integral equations (an equation of this type was named in his memory, see Davis 1960), polynomial series, differential geometry. As an expression of gratitude, he was elected as member of several scientific societies from France, Germany, Italy and was awarded with the French Order Lgion dHonneur. He was also a member of the Romanian National Astronomical Committee and of he International Astronomical Union. Professor Gheorghe Bratu employed Ioan Armeanca at the Astronomical Observatory of Cluj-Napoca in 1924, then he sent him to Germany, for Ph.D. studies in Astrophysics at the University of Gottingen (1930 1933). Ioan Armeancas Ph.D. thesis title was Photographische und photovisuelle Helligkeiten von polnahen Sternen, published in Zeitschrift fr Astrophysik, in 1933. The subject of his Ph.D. thesis comprised the standard sequence extension (Northern Polar Sequence) to all the stars from a region of 100 100 . In this way, Ioan Armeanca determined photographic brightness of 260 stars of magnitude smaller than 16.25, and photovisual brightness of 220 stars of magnitudes smaller than 14.71. In order to complete his knowledge in stellar photometry and specially in photoelectric observations, introduced at several German observatories, Ioan Armeanca worked in Germany between 1937 and 1938, mainly at Berlin-Babelsberg, where he performed photoelectric measurements with the worldwide newest Guthnik photometer. Upon his return in Romania, in 1939, he managed to buy a Guthnik photoelectric photometer, made by Toepher House in Potsdam and used for observation purposes in Cluj-Napoca Observatory. This photometer was mounted to the Newton telescope and observations were conducted in order to determine the functioning parameters of the equipment. He completed a schedule for variable stars observations. The Second World11The Astronomical Observatory of Cluj Napoca: 90th AnniversaryWar brought the relocation of the Astronomical Observatory to Timioara, where the Guthnik photometer suffered damages during bomb firing in the city. After the war, the Professor targeted his efforts toward setting up a photometric laboratory, when he ordered an optical wedge Graff visual photometer from Carl Zeiss, used for observations of comparison stars and for several variables. He also bought a Reinfelder Hertel refractor (13/140 cm), which was used for visual photometric observations of variable stars and solar observations. In the same period, Professor Ioan Armeanca made a theoretic study of micrometrical screw of the Prin refractor, which he used for the measurements of 91 double stars. After 1948, he made visual observations to RW Com and AB Cas, results that were published later by his fellow-workers. He also managed to complete and publish a comprehensive study on the 1937 Finsler comet brightness. For the theoretic training of young astronomers in the study of variable stars, Professor Ioan Armeanca organized the Astrophysics workshop still delivered to date. In 1943, he initiated a collection of monographies entitled The Cluj Astronomical Observatorys Publications, which contained nine published papers (until 1952, which marked the end of this collection). Ioan Armeanca was elected as a member of the Romanian National Astronomical Committee, since its foundation in 1928, and of several scientific societies from Germany and France. He was also a member of the International Astronomical Union and participated with Professor Bratu to the fifth General Assembly of the IAU, in Paris, in 1935. All these lead us to conclude that Professor Armeanca was the first great Romanian astrophysicist. Ioan Curea (19011977) was perceived as a remarkable researcher since his Ph.D. thesis: The Celestial North Pole Determination using Astrographic Methods. His method was later used by other observatories all around the world. The formulae proposed for determining the differential correction in pole are referred to by the renowned Russian astronomer Konstantin Kulikov as Curea relations. In 1939, the seismic unit of Cluj was reestablished by Professor Ioan Curea, who devised a linear approximation method in determining soil oscillations. His was also interested in the study of the sinusoidal seismic waves, some of them carrying his name; he edited seismic bulletins of Cluj-Napoca and Timioara units, a stellar atlas and an Astronomy course in two volumes (Timioara, 1971). Since Professor Ioan Curea established in Timioara upon the end of war, he became strongly connected with the foundation of the seismic unit, the Astronomical Observatory and Planetarium of Timioara, the artificial Earth satellites tracking station (COSPAR code number 1133), and the greatest university of this city, which he led as the first Rector. Constantin Prvulescu, the Director of the Astronomical Observatory, and also Professor of Astronomy within the Faculty of Sciences of the University refugee at Timioara (19411945), was the founder of the Romanian researches in the fields ofVasile POP, Ovidiu FURDUI, Vasile MIOC12galactic astronomy, clusters, galaxy rotation and extragalactic astronomy researches, as well. After the return from retreat, the re-establishment of the Astronomical Observatory in Cluj-Napoca and upon the death of Professor Ioan Armeanca (1954), the existing traditional communication with the West-European observatories from France, Germany and Italy were interrupted and reoriented to the Soviet Union. This operation was put in place by Professor Gheorghe Chi, the disciple of Gheorghe Bratu, while leading the destiny of Astronomy in Cluj-Napoca between 1954 and 1977. His Ph.D. thesis, The Accurate Orbit of the Comet 1937 b Whipple was defended in 1949, only a few years after his return from the battlefield. In the context of some official visits of great Soviet Astronomy personalities at Cluj-Napoca, among whom: Boris Kukarkin, Alla Massevich, Viktor Ambartsumian (who was the President of the IAU at that time), a number of fruitful discussions were conducted about Cluj-Napoca Astronomical Observatory opportunity of joining the research themes of some of the other USSR-satellite socialist countries. Relying on the equipment of the observatory and the scientfic skills of its research staff, Professor Chi led the researches towards the following themes: photometrical studies of binaries and pulsating stars, determining orbits of comets and artificial Earth satellites, space researches by founding the Artificial Satellites Tracking Station (COSPAR code: 1132), and participating in international programs as Interobs, Atmosphere, Interkosmos, Eurobs, Spin. All these programs dealt with the study of Earths high atmosphere structure parameters variation, connected to solar and geomagnetic activity, using both photometric and position observations of artificial Earth satellites. Starting from 1948, Gheorghe Chi conducted visual observations of some photometric binary stars and became the first Romanian astronomer to have published times of minima for such systems (TZ Lyr, SZ Her, KR Cyg, (1952), and also a light curve of BR Cyg binary (1953). Professor Chi also had valuable contributions in the study of 18 photometric binary systems, his efforts in this field having been crowned in his appointment as the head of Variable Stars 5th Commission within the international cooperation between the Academies of the East-European countries in Physics and Evolution of Stars. In the Romanian Astrophysics, he also introduced the systematic study of RR Lyr pulsating stars (he studied seven stars of this type), along with his scientific team (Ioan Todoran, tefan Radu, Vasile Ureche, Vasile Pop, Gheorghe-Dorin Chi). Professor Vladimir Tsessevich, the Director of the Astronomical Observatory of Odessa and one of the greatest scientific personalities of Astronomy, appreciated and mentioned our scientific activity in his RR Lyrae Stars monography. Between 19521957, along with Ioan Todoran and Elvira Botez, Gheorghe Chi performed observations on 16 small planets and four comets. He also worked on determining the Dacian astronomical orientations in the Sarmizegetusa Regia sanctuary (Graditea Muncelului), and hence he is the founder of the archaeoastronomical13The Astronomical Observatory of Cluj Napoca: 90th Anniversaryresearches in Romania. His lectures and conferences delivered all over the country recommended Professor Chi as a great Astronomy promoter. After 1961, when the Astronomical Observatory was re-transferred from the Romanian Academy to the Babe-Bolyai University, the teaching and research team included: Gheorghe Chi (since 1936), Ioan Todoran (since 1951), Elvira Botez (since 1951), Arpad Pal (since 1957), Vasile Ureche (since 1960), Ioan Mihoc (since 1963), Tiberiu Oproiu (since 1964), Vasile Pop (since 1967), Gheorghe-Dorin Chi (since 1968), Georg Paul Horedt (since 1968), Vasile Mioc (since 1971), Eugenia Radu (since 1973), then Mihail Brbosu (since 1988), Ferenc Szenkovits (since 1995), Cristina Blaga (since 1991), Radu Zapotinschi (since 1996), Zoltan Mako (since 1997). This was the most successful period, when tens of thousands of visual, photoelectric and photographic observations on different types of variable stars and over 50,000 position observations were performed on artificial satellites, with results published in many international journals. In literature, special astronomers were referred to, like Ioan Todoran, who observed and studied 49 photometric binary systems and 14 pulsating stars, Vasile Ureche and Vasile Mioc for their theoretic models, Tiberiu Oproiu and Vasile Mioc for satellite dynamics. Within the scientific seminar founded in 1947 by Professor Ioan Armeanca and later led by Professors Gheorghe Chi (19541977), Vasile Ureche (19772000), and Vasile Pop (20002005), hundreds of studies were discussed and conducted on the following astrophysical topics: Period variation of the close binaries by apsidal line shift, the presence of the third body, the systems evolution in the mass transfer phase; The close binary systems light curves processing, using new models devised, such as the ellipsoid-ellipsoid model; Determining absolute elements in the binary systems components; Roche surfaces and stellar stability; The photometry of some RR Lyrae pulsating stars and classical Cepheids, light curves, multiple periods, Blazhko effect, physical parameters determination; The adjustment spline functions methods and several iterative methods in determining variable stars times of maxima and minima; The pulsation of rotating and tidal perturbed stars theory; Structure properties, stability constraints, continuum spacetime geometry, and gravitational field of relativistic stars; Different types of polytropic, barotropic and relativistic stepenar stars, or white dwarfs. After completing his studies in Celestial Mechanics at the Lomonosov University of Moscow, where he also obtained his Ph.D., Arpad Pal was promoted as scientific researcher in the Astronomical Observatory (1957) and later Assistant Professor at the Jnos Bolyai University (where students made studies in Hungarian), which becameVasile POP, Ovidiu FURDUI, Vasile MIOC14Babe-Bolyai University in 1959, after its fusion with Victor Babe University. In 1972, Professor Arpad Pal initiated and led the Celestial Mechanics and Space Research seminar, which hosted many researches and publications (much appreciated abroad) on the following topics: Study of artificial Earth satellites (EAS) perturbed motion under the influence of different gravitational and nongravitational factors; AES orbits determination and improvement; Evolution of the high atmosphere state parameters using observational data concerning the AES orbital drag in the atmosphere; Elaboration of various algorithms and computing programs in order to determine the AES ephemerides; Mathematical models for the elliptic case of restricted three body problem; Lie mappings method in the study of the celestial bodies perturbed motion; Topological methods and differential manifolds with their applications in Celestial Mechanics; The two- and n-body problems collision and escape solutions; The two-body problem in the Manev-type gravitational field and in many other post-Newtonian fields. The generalized Gyldn problem (the equivalent gravitational parameter problem); After the reorganization of many Romanian institutes in 1977, the researchers belonging to the Cluj-Napoca Observatory were included in the CASS (Centre for Astronomy and Space Sciences) of Bucharest, the Astronomical Institute of the Romanian Academy nowadays. Today, the Cluj-Napoca Observatory of the Institute includes the following members: Dr. Tiberiu Oproiu (since 1964), Dr. Alexandru Pop (since 1987), Dr. Rodica Roman (since 2002), Dr. Iharka Csillik (since 2002), Dr. Ovidiu Furdui (since 2008), Vlad Turcu (since 1990), Liviu Mircea (since 1992), Dan Moldovan (since 1995). This team managed to purchase a MEADE 16" LX 200 type reflector (40/406 cm) and introduced the CCD photometry for the first time in both Cluj-Napoca and Romania. They also managed to perform highly accurate observations and light curves for several variable stars. The departments teaching staff was also renewed with the employment of: Associate Professor Mihail Brbosu, Associate Professor Ferenc Szenkovits, Associate Professor Cristina Blaga, Assistant Radu Zapotinschi, who work in a very friendly and cooperatively manner with their colleagues from the Cluj Branch of the Romanian Academy. Professor Vasile Pop also works today as a researcher of the Astronomical Institute of the Romanian Academy in the Observatory of Cluj-Napoca. Dr. Vasile Mioc, who worked 26 years at this Observatory, became in 2005 the Director of the Astronomical Institute.15The Astronomical Observatory of Cluj Napoca: 90th AnniversaryWithin the Cluj Napoca Astronomical Observatory and Babe-Bolyai University, more than 40 Ph.D. theses in Astronomy were directed (especially by Professors Gheorghe Chi, Arpad Pal, and Vasile Ureche) and successfully defended. We mention here only some todays significant names in the Romanian astronomy: Tiberiu Oproiu, Nicolaie Lungu, Vasile Pop, Vasile Mioc, Magda Stavinschi, Gheorghe Vass, MariaMagdalena Crmaru, Eugenia Radu, Dan elaru, Ctlin Cucu-Dumitrescu, Alexandru Dumitrescu, Ferenc Szenkovits, Rodica Roman. We have to mention that two researchers of the Cluj-Napoca Observatory were appointed as Ph.D. advisors: Dr. Tiberiu Oproiu (since 1990) and Dr. Vasile Mioc (since 1994, when he still was working in Cluj-Napoca). Researchers of the Astronomical Institute of the Romanian Academy (and not only) elaborated and defended Ph.D. theses under their direction. Along the last decades, the astronomers from Cluj-Napoca published dozens of books, among which we quote: Mathematical Processing of Experimental Data. Empirical Functions by Ioan Todoran (1976); Chronicle of Romanian Astronomical Observations by Vasile Mioc and Damaschin Mioc (1977); The Eclipses and their Foresight by Ioan Todoran (1977); As Close as Possible to Stars by Ioan Todoran (1977); Space Rockets by Vasile Mioc and Tiberiu Oproiu (1978); Todays Astrophysics by Vasile Ureche (1978); Explosions in the Universe by Ioan Todoran (1979); The Comets by Vasile Mioc (1980); The Universe (two volumes: 1982, 1987) by Vasile Ureche; Stellar Pulsations. Mathematical Theory by Nicolaie Lungu (1982); The Book of the Amateur Astronomer by Ioan Todoran (1983); Astronomy (by Arpad Pal, Vasile Ureche, 1983; the first published course following a curriculum released by the Ministry of Education); Astronomy. Collection of Exercises with Solutions by Arpad Pal, Vasile Pop, Vasile Ureche (1998; a collection of exercises for this curriculum); Astronomy of the Invisible by Ioan Todoran (1989); Gomtrie Riemannienne et systmes dynamiques. Applications by Mihail Brbosu (2000); Methods for the Analysis and Interpretation of Stellar Variability by Alexandru Pop (2000); Our Solar System by Cristina Blaga (2001); Topological Methods in Celestial Mechanics by Ferenc Szenkovits (2002); The Roche Model of Double Stars by Rodica Roman (2003); Planar and Spherical Trigonometry by Vasile Pop and Drago Pop (2003);Vasile POP, Ovidiu FURDUI, Vasile MIOC16 Methods of Regularization in Celestial Mechanics by Iharka Csillik (2003); Observational Astronomy by Vasile Pop and Cristina Blaga (2005). It should be also noticed that, along many years, the official textbook of astronomy for high-school education was the one published by Professor Gheorghe Chi (Astronomy, 1965). All this constitutes an incontestable evidence of the important role played by the Cluj-Napoca Astronomical Observatory in the Romanian scientific life. As a final remark, the bibliography on the Cluj-Napoca Astronomical Observatory is huge, and impossible to be reproduced within the framework of a review paper. So, we direct the reader to the countless quotations on Internet.Received on 20 July 2009