Astronomical Observatories

OSSERVATORI ASTRONOMICI. -

I. HISTORICAL NOTES

Leaving aside the very ancient Chinese astronomical observatories, about which the information is highly uncertain, it is known that in the classical world the first observatories appeared in Mesopotamia, perhaps around the 10th century B.C., and consisted of tall, multi-level pyramidal towers (the ziggurats of the Babylonians), some remains of which have been found at Horsabad, near Nineveh. As is well known, the Chaldean priests (whom V. astronomy) were assiduous students of the stars and celestial movements; indeed, they had succeeded in discovering a practical method (the so-called Saros cycle) for the approximate prediction of solar and lunar eclipses.

From Chaldea, astronomy passed to Egypt and then to Greece; and, after the Macedonian conquest, the center of study moved from Athens to Alexandria in Egypt, which flourished under the rule of the Ptolemies, who founded there the famous museum, with a very rich library and a celebrated astronomical observatory described by Eratosthenes (276-196 B.C.), one of the greatest astronomers of antiquity. The Alexandrian astronomical school came to an end, so to speak, with Claudius Ptolemy (2nd century A.D.), who in his Almagest summarized the knowledge of past generations.

With him the ancient era of astronomy came to an end and the astronomical Middle Ages began. During the Middle Ages astronomy was cultivated extensively by the Arabs, who translated the Almagest into their language (later translated into Latin by Gerardo da Cremona in 1180) and carried out many observations of planets and comets with their astrolabes and triquetra. A precious Arab astrolabe, constructed at Valencia in 1175 by Sa'id Ibrāhīm, is preserved in the Astronomical Museum of the Observatory of Rome on Monte Mario.

Among Arab astronomical observatories, particular mention should be made of that of the astronomer al-Battānī (Albatenius) in Mesopotamia (10th century), and that of Ulugh Beg at Samarkand (Turkestan); the works of al-Battānī, discovered in the Library of the Escorial, were recently published by A. Nallino in the Arabic text with a Latin translation.

With the beginning of the modern age, genuine astronomical observatories also arose in Europe. Among the earliest, preceding the discovery of the telescope, were that of Kassel (Germany), erected in 1561 by Guglielmo IV, Landgrave of Hesse, and the celebrated observatory of Tycho Brahe on the island of Hven (Baltic Sea), where the great Danish astronomer carried out those methodical and exact observations of the position of the planet Mars that later led Kepler to discover the famous three laws governing the heliocentric motion of the planets. But a true flourishing of astronomy took place only after the invention of the telescope (1609) and Galileo’s first discoveries concerning sunspots, the mountains of the Moon, the phases of Venus, the satellites of Jupiter, the Milky Way, etc.

The following century therefore saw the foundation of the great European observatories: Paris (1667), Greenwich (1675); Berlin (1705); St. Petersburg (1725); Vienna (1735), etc.

With particular regard to Italy, mention should be made in Rome of the Observatory of S. Maria in Vallicella, founded by Ponteo, who there made observations of the comet of 1680—observations that had the honor of being mentioned by Newton himself. This is the first Italian observatory of which there is any record, since the earlier observations of Clavio, Scheiner, and E. Divini had been carried out on terraces with portable telescopes; it was followed by the observatory of the University of Bologna, founded in 1714. A few years later, the Jesuits who resided in the Palazzo di Brera in Milan, where they taught courses in philosophy and theology, founded the Milanese observatory (1760), appointing the illustrious mathematician and astronomer Fr. Ruggero Boscovich as its director. Shortly afterward (1766), by decree of the Venetian Senate, the Observatory of Padua was established in the tower of Ezzellino; then Fr. De Caesaris founded the Caetani Observatory in Rome (1780), near S. Maria Maggiore, later transferred to the Campidoglio, while a few years afterward (1787) Abbot Giuseppe Calandrelli founded the Observatory of the Collegio Romano in a small tower that he erected on that building and which is still visible from the square of the same name.

After the storm of the French Revolution had passed, Abbot Giuseppe Piazzi (who, some years earlier, had founded the Observatory of Palermo on the tower of S. Ninfa and had greatly distinguished it through the discovery of the first minor planet, Cerere Ferdinandea) was invited by Ferdinando I to complete and direct the Observatory of Naples, whose construction had recently been begun at Capodimonte (1812). Later (1823), Pope Leone XII reorganized studies with the brief Quod divina sapientia and decreed the foundation of an observatory on the great eastern tower of the Palazzo del Campidoglio in Rome; this foundation was entrusted to Abbot Feliciano Scarpellini, who transferred to the Campidoglio the equipment of the old Caetani observatory, which he had directed, and added new scientific instruments. At almost the same time, G. Plana founded the Observatory of Turin on one of the towers of Palazzo Madama; D. De Vecchi established the Observatory of Florence in the Palazzo del Museo delle scienze, etc. The end of the 19th century saw the establishment (1888) of the Vatican Observatory, then situated atop the Leonine Tower in the Vatican walls.

II. MODERN ASTRONOMICAL OBSERVATORIES

With the beginning of the twentieth century, astronomical observatories completely abandoned the old towers in which they had always been housed, and instead required the possession of a piece of land (preferably on a hill) on which to place, in separate pavilions, the instruments intended for measuring the positions of the planets and stars (transit instruments, meridian circles, etc.). Indeed, the great precision now required in positional measurements demands that these instruments have maximum stability and therefore be placed directly on the ground, upon extremely solid foundations. Moreover, the increasingly widespread use of celestial photography, especially in astrophysics for the study of nebulae, stellar spectra, etc., often recommends taking such photographs under particular conditions, for example, in the mountains. On the other hand, the photographic plates thus obtained must subsequently be measured and studied with the utmost care; and practice has shown that for every hour spent photographing the sky, fifty or seventy hours at the desk are then required for examining the plates. But nothing requires this lengthy examination to be carried out in the same place where the photographs were taken; furthermore, the large observatories often possess rich libraries, provide time-signal services, etc., and also house advanced courses for students, so that it would be detrimental to move them far from the city and the great universities. The problem has therefore been solved by equipping modern observatories with suitable “branch observatories.”

Thus, for example, as regards Italy, the astronomical observatory of Rome abandoned its ancient urban sites and moved to the summit of Monte Mario, on the prime meridian of Italy, placing the positional instruments in separate pavilions in the park; it has also recently established a branch station on the Gran Sasso d’Italia, at an elevation of 2,300 m above sea level. Similarly, the observatory of Bologna established a branch station at Loiano in the Apennines; that of Padua at Asiago, at an elevation of 1,000 m; that of Milan at Merate, etc. Likewise, the observatory of Turin was moved by its director, G. Boccardi, from the towers of Palazzo Madama to a suitable park near Pino Torinese; the observatory of Florence, through the efforts of G. B. Donati, moved from the old Palazzo del Museo to the hill of Arcetri near the city. Most recently, the Vatican Observatory, under the direction of the Jesuit Fr. J. Stein, also left the old Leonine tower for the papal park at Castel Gandolfo.

But the great advances of astronomy have led to a further specialization of astronomical observatories. At present, it is inconceivable that a single observatory could concern itself with every field of astronomy, just as no institute today could profitably concern itself with every field of medicine. Modern observatories therefore tend to be divided into astronomical observatories properly so called, whose duties concern chiefly positional astronomy, or classical astronomy; astrophysical observatories, which are primarily concerned with the physical constitution of the heavenly bodies; solar observatories, which study the sun; and finally astronomical laboratories, devoted particularly to calculations and to the examination of photographic plates obtained at other observatories.

Naturally, purely geodetic observatories are excluded from consideration (in Italy, the observatory at Carloforte, which is concerned with the movements of the Earth’s pole), as are meteorological and seismic observatories, which observe meteorological phenomena, earthquakes, microseisms, etc.; it should be noted that this classification is neither is nor can be absolute, but is merely intended as a guide. Thus, for example, there are observatories that are simultaneously astronomical and solar, or astrophysical and solar, astronomical and meteorological, astronomical and seismic, etc.

At present, the United States is undoubtedly the nation in which astronomy is cultivated to the greatest extent, both because of the large number and because of the high capabilities of the observatories at its disposal. It will suffice to recall those on Mount Palomar, Mount Wilson, and Mount Hamilton, as well as Lowell Observatory, etc.

III. ASTRONOMICAL INSTRUMENTS

The principal instruments of observatories are: the high-precision clock, the meridian telescope, the equatorial telescope (visual or photographic), the astrograph, the reflector, and the solar tower; the first are chiefly associated with astronomical observatories, the last with astrophysical and solar observatories.

Clocks are generally installed in basements or in rooms maintained at a constant temperature; often, too, under pneumatic bells at constant pressure. Meridian telescopes, installed in separate pavilions in the observatory park or garden, are of modest dimensions and can move only in the plane of the meridian; they are therefore suited to determining the precise instant at which a celestial body crosses the meridian, as well as the altitude it reaches at that moment above the horizon. From these observations the astronomer derives the celestial coordinates of the body under examination (right ascension and declination), the correction of the clock, and the longitude and latitude of the observatory. Equatorial telescopes are large telescopes (the largest, belonging to the Yerkes Observatory, has a lens more than one metre in diameter) installed beneath revolving domes; they are used for the study of double stars and variable stars, for the determination of stellar parallaxes, for examining the physical peculiarities of the planets, etc. For this purpose they have a special mounting (called equatorial) and are moved by an electric motor, which enables them automatically to follow a celestial body in its apparent motion across the sky, from rising to setting. Astrographs are photographic equatorials of modest dimensions, but equipped with a system of lenses that enables them to photograph a wide region of the sky; they are especially useful for locating and determining the positions of minor planets and comets. Reflectors are large equatorials in which the objective lens is replaced by a parabolic mirror (or a spherical mirror, in the modern Schmidt type); since the mirror concentrates at the same focus all light rays, whatever their wavelength, and since it can be constructed in very large dimensions (that of Mount Palomar has a diameter of 5 m), the reflector may be regarded as the principal instrument of astrophysics for the study of stellar spectra, the photography of extremely distant nebulae, etc. The solar tower is a tall tower (that at Mount Wilson is approximately 50 m high; that of Monte Mario in Rome, the largest in Italy, approximately 35 m) which supports within it a vertical telescope whose length is equal to the height of the tower. At its summit, beneath a revolving dome, there is a system of movable mirrors (a coelostat), which directs the solar rays onto the objective lens of the telescope.

The astronomer takes up position in a room on the ground floor of the tower, where a large focal image of the Sun is formed, which he can study or photograph with ease. In the basement there is another apparatus (spectroheliograph), which permits the spectroscopic study of individual regions of the Sun, as well as photography using only the light emitted by certain chemical elements, hydrogen, calcium, etc. This makes it possible to determine the distribution and movements of clouds of calcium, hydrogen, etc., in the upper layers (chromosphere) of the Sun.

For the sake of brevity, we shall merely mention here the auxiliary astronomical instruments (micrometers, photometers, chronographs, spectrographs, plate-measuring instruments, calculating machines, etc.), as well as meteorological and seismic instruments (barometers, thermometers, hygrometers, anemometers, seismometers, etc.), while also recalling that some observatories possess rich libraries and sometimes (for example, the Rome Observatory) an astronomical museum as well. - Vedi tav. XXVIII.

By contrast, in the second half of the last century, other scientific observatories were established.

In Manila, the Jesuits founded a meteorological station in 1865 which, under the direction of Fr. Federico Faura y Prat, a Spaniard, soon developed into the Observatory of Manila. Although the Fathers’ initial concern was the forecasting of typhoons, geomagnetic, seismological, and astronomical sections were soon added to the meteorological section. It was, however, completely destroyed in February 1945, when the Japanese army evacuated the city. Fr. Faura became widely known for inventing an instrument for forecasting typhoons.

The Observatory of Zi-ka-wei, near Shanghai, which in a certain sense marks the revival of the ancient imperial Observatory of China, was founded by the French Jesuits in 1873. Fr. Luigi Froc, known as the “Father of typhoons,” and his successor, Fr. Ernesto Gerzi, rendered great services to the economic and commercial development of that Chinese coast through their increasingly accurate and reliable forecasts of typhoons. From the scientific point of view, however, the work of the other sections established at the Observatory of Zi-ka-wei and at its branch at Zo-sè was no less important. For meteorology, the Observatory published a Bulletin de prévision de temps (daily), and for astronomy, Annales de l'Observation de Zo-sè. Among the more recent and important publications of Fr. E. Gherzi, mention may be made of La météorologie de la Chine (published by the Pontifical Academy of Sciences [Rome 1939]) and Climatological atlas of Asia (Shanghai 1944). In 1950, the buildings were occupied by the communist government of China.

Of lesser importance is the Observatory of Ambohidempona on the island of Madagascar, founded in 1889 by the French Jesuits. For some time, in collaboration with government institutions, the Fathers devoted themselves to the study of cyclones, which are fairly rare in that region. The most important work of that observatory, however, consists of geomagnetic research, conducted by its present director, Fr. Charles Poisson. It also has sections for astronomy, seismology, and meteorology. It likewise had an important geodesy section.

In 1907, the French Jesuit Fr. Bonaventura Berloty founded the Observatory of Ksara in Lebanon, which forms part of the University of St. Joseph in Beirut. From 1911 until 1944, the official direction of the State Meteorological Service was combined with that observatory. In addition to the meteorological section, it comprises astronomical, geomagnetic, and seismological sections. The climatological study of Lebanon constitutes its most important work. Until 1940, the Observatory published: Annales de l'Observatoire de Ksara, and until 1945: Climatologie aéronautique. It now publishes monthly: Bulletin mensuel de climatologie and Bulletin sismologique prévisoire.

Fr. Edward Pigot, an Irish Jesuit, founded in 1908 a seismological station which developed into the Astronomical and Seismological Observatory of Riverview, near Sydney in Australia. The present director is Fr. Daniel O'Connell. The principal work of that observatory consists in photographic photometry, especially of variable stars.

Since in the mission countries governments always wish to have their own observatories, it is expected that observatories in the missions will gradually lose some of their public importance and will instead be transformed into scientific research institutes affiliated with universities or colleges directed by missionaries. Alfonso Smeters