Astronomy

ASTRONOMY. - Among ancient peoples, astrology (v.) was the mother of astronomy. Since, according to the common opinion, the destiny of men depended on the constellations, on the positions and groupings of the planets, in order to be able to forecast a configuration favorable to an undertaking of some importance it was necessary to observe the celestial phenomena assiduously in order to deduce from them their periodic returns. From observations of the sun the Chinese determined the length of the solar year as 365.25 days, and probably already 2000 years B.C. they knew the so-called Metonic cycle of 19 years, after which the lunar phases repeat on the same dates of the year. Among the Babylonians observations began in the 23rd century B.C. and, continued for many centuries, led to the laws of the motions of the sun, of the of the moon and of the planets among the stars. They knew the four lunar periods: synodic, sidereal, anomalistic, draconitic, and the Saros, a cycle of 18 years and 11 days, which makes it possible to predict the times of solar and lunar eclipses.

In antiquity the absolute immobility of the Earth and its central position in the world were accepted by almost universal consent. In the 5th century B.C. Philolaus, a native of Taranto, whence he emigrated to Thebes in Boeotia, supposed that around the center of the world there was placed a fire, around which move in a circle the five planets, then the Sun and the Moon, finally the Earth and lastly, near the central fire, the Counter-Earth. The Earth's circuit around the central fire is accomplished in the space of one day: and this same condition, combined with the other, that the face of the Earth is always turned outward, produces day and night, and the apparent daily revolution of all the stars, including the Sun and the Moon. The Counter-Earth, remaining always on the unknown side of the Earth, is never visible. While then Eudoxus (408-365 B.C.) and Aristotle (384-322 B.C.), rebelling against such a conception, created the system of the Sun homocentric to the immobile Earth, Heraclides Ponticus (4th century B.C.) taught the rotation of the Earth around its own axis, and the revolution of Mercury and Venus around the Sun as center, anticipating the Tychonic system. Meanwhile an unknown contemporary of Heraclides notes that the inequalities of the planets produced by the Sun are explained not only by making the planets circle around the Sun and the Sun around the Earth, but also by exchanging the roles of the Sun and the Earth, that is, by placing the latter in the number of the planets. Thus the idea of Copernicus was fully reached, which was later adopted by Aristarchus of Samos (310-230 B.C.) and by his pupil Seleucus the Chaldean.

Unfortunately the Greek astronomers after Aristarchus took no account of these remarkable advances, and stubbornly maintained as the foundation of their calculations always the hypothesis of the immobile earth. The most celebrated is the great Hipparchus, who applied trigonometry to astronomy and from his observations (made between 161 and 126 B.C.) composed a catalogue of 1080 stars. Comparing his positions with those observed 150 years earlier, he discovered the phenomenon of the precession of the equinoxes. Three hundred years later, the work of the observers came to completion in the synthesis of the great observer of ancient astronomy, Claudius Ptolemy (v.). In the Almagest, he set out his geocentric system: the Earth, spherical in shape, stands immobile at the center of the universe; around it the celestial sphere rotates in the daily motion from east to west; with this motion are combined the various motions of the seven planets: Moon, Sun, Mercury, Venus, Mars, Jupiter, Saturn, from west to east on planes sensibly parallel to the ecliptic. To reduce all celestial phenomena to uniform circular motions, he adopted a very complicated system of deferents and epicycles.

Ptolemy's system remained dominant throughout the Middle Ages. Then it came to collapse through the work of the great reformer of astronomy, the canon of Frauenburg, Nicholas Copernicus (v.), who in his immortal work De revolutionibus orbium coelestium (1543) places the Sun at the center of the planetary system. About 70 years later, Kepler found his three laws, which govern the elliptical motion of the planets, and in 1687 Newton demonstrated that those laws were a necessary consequence of his law of universal gravitation: two bodies attract each other with a force directly proportional to their masses and inversely proportional to the square of their mutual distance.

Descriptive astronomy begins with the invention of the telescope at the beginning of the 17th century. Its application to astronomy, first made by Galileo, led to a multitude of wonderful discoveries: the satellites of Jupiter, the phases of Venus, the mountains of the Moon, the spots of the Sun, the stellar composition of the Milky Way, and the appendages of Saturn, whose annular nature was discovered by Huyghens in 1656, who also discovered the largest satellite of Saturn, Titan, which was followed by the discovery of four other satellites made by Cassini (1671-72, 1684). The return in 1759 of the comet of 1682, predicted by Halley, gave the first proof of the existence of periodic comets. Of these, thirty-eight are known so far whose return has been observed and of which 27 have periods of less than 10 years. When, in 1781, W. Herschel began to scan the sky, he had the good fortune to find the planet Uranus, in 1787 two satellites of the same and in 1789 the 6th and 7th satellite of Saturn. On January 1 of the year 1801 the Theatine father Giuseppe Piazzi discovered Ceres, the first of that swarm of asteroids between Mars and Jupiter, whose number now surpasses 1600. A new era of discoveries began when Leverrier, from the perturbations of the orbit of Uranus, found by calculation alone the planet Neptune (1846), whose only satellite was found a month later by Lassell. There follow the 8th satellite of Saturn (Bond, 1840), two other satellites of Uranus (Lassell, 1851), the two satellites of Mars (Hall, 1877), the 5th satellite of Jupiter (Barnard, 1892), the 9th and 10th of Saturn (W. Pickering, 1898, 1904), the 6th and 7th of Jupiter (Perrine, 1904-1905), the 8th (Melotte, 1908), the 9th, 10th and 11th of the same (Nicholson, 1914-38), and finally the trans-Neptunian planet Pluto, found by Tombaugh (1930) near the place assigned to it by Prof. Lowell in a memoir of 1915. A 5th satellite of Uranus was found in 1940 by Kniper.

In 1866 Schiaparelli demonstrated that the swarms of shooting stars of August, called "tears of St. Lawrence" or Perseids, follow the orbit of the comet of 1862. Likewise it was found that the Leonids, shooting stars of mid-November, follow the orbit of Tempel's comet of 1866. Similar connections were found between the other swarms and known comets. Whence it was concluded that these swarms are the product of a partial disintegration of comets, the nuclei of which are constituted essentially by a mass of meteorites.

To sum up: the planetary system counts 9 great planets, 30 satellites, more than 1600 asteroids, 38 periodic comets, besides the Sun, which has a mass about 800 times greater than that of all the planets taken together. The mean distance of the Earth from the Sun is 149,673,000 km.; that of Pluto is ca. 40 times greater.

The application of spectral analysis to the study of celestial bodies was begun by Fraunhofer and by Kirchhoff, the latter of whom in 1861 drew a map of the solar spectrum. Of fundamental importance was the work of Father Secchi (v.), who after a systematic examination of 4000 stars, reduced their spectra to 4 types: a classification that was very soon universally accepted. From spectral analysis it follows that the matter of the Sun and of the stars is identical to that of the Earth. The temperature of stellar photospheres varies from 3000 to 23,000 degrees. That of the Sun is ca. 5700°; in the interior the temperature goes on increasing, and at the center, according to Eddington, it is ca. 40 million degrees, while the central density is 28 times that of water. In that burning furnace, from sub-atomic processes, is developed the enormous energy radiated by the Sun, equivalent, per minute second, to a number of kilowatt-hours which is written with 21 digits. And yet our Sun, with its diameter of 1,390,000 km., is rather a dwarf star, in comparison with the giant stars and super-giants, whose absolute luminosity surpasses that of the Sun by as much as 20,000 times and more. Giants of enormous dimensions are, for example, Betelgeuse and Antares, with radii respectively 300 and 450 times that of the Sun, that is, equal to 1½ times the semi-axes of the orbits of the Earth and of Mars, but with a density of barely 1/3000 of atmospheric air. On the other hand, there are dwarf stars of dimensions smaller than that of the planet Uranus, indeed of the Earth, but with a density of more than 50,000 times that of water.

Not all stars shine with an invariable brightness. Already more than 9000 variable stars have been discovered, some of which vary irregularly, others with more or less regular periods. One distinguishes variables with a short period (from a few hours up to two months) and those with a long period (from four months up to two years and more). The short-period variation is for the most part caused either by the mutual eclipses of the components of a double star, or by the pulsations of a star alternately dilating and contracting. The cause of long-period variations is still unknown. The Sun too, with its eleven-year period of sunspots, is a slightly variable star.

Among the variable stars a singular place is reserved for the new stars: luminaries that suddenly ascend from a minimum to a maximum of splendor, then descend, first rapidly, then progressively or with periodic oscillations, to their normal magnitude. Today one can say with certainty that the phenomenon of a new star consists substantially in the explosion of a star, although the intimate cause of the explosion remains hitherto unknown. Following this explosion, the outer layers are violently projected, and the phenomenon appears to us as an enormous increase in the diameter of the star, with a very great increase in total splendor. Disper-

then the expelled matter dispersing into space, the brightness gradually diminishes.

In recent years, searching the nebulae outside the Milky Way for new stars, a particular kind was discovered, which were called supernovae because of the intensity of their light, which at maximum is on average equal to 50 million times that of the Sun, varying between 2.5 and 1100 million times. So far about fifty supernovae have been discovered. The famous new star of Tycho Brahe of 1572 probably belonged to that class as well.

Of the utmost importance was the application of photography to astronomy. It has enabled us to number, measure, and catalog millions of stars, to determine their positions, size, and movements, to sound the depths of cosmic space, and to admire the wondrous greatness of creation. Today we know that the Milky Way has a diameter perhaps far exceeding one hundred thousand light-years, that its center lies in the direction of Sagittarius at a distance from the Sun of about 30 thousand light-years, and that this immense family of stars must be reckoned at several hundred billion stars, a great part of which, united in pairs, triples, or more, describe their orbits as double or multiple systems according to the law of universal gravitation. Our stellar system is a complex of star clusters, of loose groupings such as those of the Pleiades, the Hyades, the Manger, of luminous and dark nebulae, masses of gas of an unimaginable tenuity or of solid corpuscles, from tiny specks of dust to fragments the size of a fist and beyond, dark clouds, such as those of the great bifurcation of the Milky Way, which absorb part of the light of the stars behind them, of about a hundred compact globular clusters, each consisting of a hundred thousand stars. Very probably our galactic system has the flattened shape of a spiral nebula, in which all the stars revolve, in a period of about 200 million years, around the central mass, estimated as equal to 70 billion solar masses.

Outside the Milky Way there exist millions of similar stellar systems: the nearest of these, at a distance of 800,000 light-years, is the spiral nebula of Andromeda, visible to the naked eye as a faintly luminous patch. It has a diameter of at least 50,000 light-years, and counts from 2 to 3 billion stars. Of such nebulae, with diameters between 10,000 and 100,000 light-years, conglomerations of several billion stars, about 30 million are perceptible with the great photographic telescopes, with which, after several hours of exposure, the most distant ones, up to 170 million light-years away, appear on the plate as barely visible traces. And when the new telescope with a 5-meter aperture is ready, the penetrable distance of cosmic space will be doubled once again.

ASTRONOMY AND SACRED SCRIPTURE

The sacred authors, having no scientific aims, speak of the world as it appears to the senses and as it was conceived in their time. In the Bible we find no reference to what modern astronomy teaches us. According to St. Augustine, it was not the Lord's intention to impart scientific teachings to us, since they do not contribute to eternal salvation. Cardinal Baronio used to say that God wanted to instruct us how to go to heaven, not how heaven goes. References to the celestial bodies are therefore rare in the Old Testament. The first visibility of the Moon determined the beginning of each month, and this was the only reference to the sky made for the purposes of the Hebrew ritual. But there is a remarkable fact: while in those times, among all the surrounding nations, the celestial bodies were objects of divination and idolatry, the attitude of the sacred authors in this regard was always absolutely impeccable. And no ancient author can compare with the great Hebrew authors in spiritual elevation, in poetic sublimity, and in admiration for the works of the Creator. "In the beginning God created Heaven and Earth": this is the great truth, revealed by God to men, whatever the meaning of the "six days" in which the creation was accomplished. "You alone are, O Lord! You have made the heavens, the heaven of heavens and all their host, the earth and all that it contains, the seas and all that is in them; You give life to all these things, and the host of heaven adores You" (II Esd. 9:6).

Venus and Saturn are the only planets mentioned in the Old Testament. "How have you fallen from heaven, O Lucifer, who shone in the morning!" thus Isaiah (14:12) addresses the chief of the demons. And the prophet Amos reproaches Israel: "You have carried the statues of your idols, the star of your god"; in Hebrew: "Kijjūn (Saturn) your idol, the star of your god."

The passages where certain constellations are mentioned are:

Job 9:9: "(God) has created the Bear, Orion, the Pleiades and the recesses of the southern sky." According to Schiaparelli, the recesses of the southern sky (interiora Austri) refer to a group of brilliant constellations, formed by Argo Navis, the Southern Cross and Centaurus, constellations that were visible in Palestine when the book of Job was written, but are no longer seen now, because of precession.

Ibid. 26, 13: "His spirit adorned the heavens, and the skill of His hand produced the twisting serpent." Probably the constellation of Draco is meant.

Ibid. 38, 31: "Can you perhaps bind together the bright stars of the Pleiades or interrupt the course of Arcturus?" The Hebrew text has Orion, instead of Arcturus.

Ibid. 38, 32: "Is it perhaps you who make the morning star appear in its time and make the Vesper be born above the children of the earth?" In the original text one reads instead: "Can you produce Mazzârôth in their station? Or can you guide 'Ajîš with its children?" Probably Mazzârôth means the planet Venus, and 'Ajîš the star group of the Hyades.

Am. 5, 18: "Seek him who created Arcturus and Orion." The Hebrew text has: the Pleiades instead of Arcturus.

II Kings 23, 5: "(Josiah) exterminated the soothsayers... and those who burned incense to Baal, to the Sun, to the Moon, to the twelve signs (Mazzârôth) and to all the host of heaven." Mazzârôth, according to many interpreters, is identical to the Mazzârôth of Job 38, 32.

These are the only allusions to specific constellations in the Old Testament. In the New Testament they are entirely lacking. As for the Star of the Magi, it is enough to pause for a moment on the particulars of the Gospel account (Mt. 2, 2, 9, 10) to understand that this account intends to present an absolutely miraculous phenomenon, which cannot in any way be brought within the stable laws of a natural meteor however rare (G. Ricciotti, Vita di Gesù Cristo, n. 174; cf. n. 253). - See Plates XXIII-XXIV.

H. Bürgel, Dai mondi lontani, trans. by A. Abetti, Turin 1946: - Scientific manuals: G. V. Schiaparelli, I precursori di Copernico nell'antichità. Scritti sulla storia dell'a. antica, I, part 1, Bologna 1925; G. Armellini, Trattato di A. siderale, 3 vols., Bologna 1928-36; E. und B. Strömgren, Lehrbuch der Astronomie, Berlin 1933; H. Spencer Jones, General Astronomy, 2nd ed., London 1934; Fr. Becker, Grundriss der sphärischen und praktischen Astronomie, Bonn and Berlin 1934; H. N. Russell, R. S. Dugan, J. Q. Stewart, Astronomy, 2 vols., 2nd ed., Boston 1945; G. Cecchini and L. Gratton, Le Stelle Nuove, in Memorie R. Acc. d'Italia, 13 (1942), p. 1; id., I fondamenti scientifici dell'A., Milan 1947. - Biblical A.: E. N. Maunder, The Astronomy of the Bible, 2nd ed., London 1908; G. V. Schiaparelli, L'a. nell'Antico Testamento, Milan 1893; G. Hagen, La Stella Magorum, in Rivista di Astronomia, 5 (1911) pp. 74-75; U. Holzmeister, La Stella dei Magi, in La Civ. Catt. (1942, 1), pp. 8-22.

Giovanni Stein