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Monday, December 11, 2017

Discoveries with the Telescope

Discoveries with the Telescope


In 1609 Hans Lippershey, a spectacle maker of Middleburg, Holland, made the first telescope. News of the invention soon reached Galileo Galilei, professor of mathematics at the University of Padua, who lost no time in making one for himself. In fact, he made several telescopes, all small and imperfect by modern standards, but powerful enough to reveal that the moon, instead of being smooth and polished as Aristotle had taught, was rough with mountains and valleys.

The sun, supposedly a perfect object, had blemishes. Dark spots drifted slowly across its face, and by their motion demonstrated that the sun, like the earth, rotated. The Milky Way, whose nature had hitherto been a complete mystery, was found to be composed of innumerable stars; the planet Venus went through phases; Jupiter had a round appearance and was accompanied by four moons; Saturn underwent strange changes and at one time seemed to have two handles attached to its disk.

Galileo Galilei before the Papal tribunal. From the painting by Joseph-Nicolas Robert Fleury

As a result of these discoveries Galileo wrote strongly in favour of the Copernican or heliocentric theory. By so doing he incurred the displeasure of the Church, and on June 22, 1633, was ordered by the Inquisition to renounce his heretical opinions. Although he was at no time tortured, he suffered great mental anguish and was placed under virtual imprisonment at Siena and his villa at Arcetri. Yet in spite of these proceedings his discoveries with the new instrument could not be ignored. Other astronomers repeated and extended his observations, and most of his critics had to admit that there was more in the universe than Aristotle and his followers had ever imagined.


The Earth Does Move


The microscope and telescope, both developed in early seventeenth-century Holland, represent an extension of human vision to the realms of the very small and the very large. Our observations of atoms and galaxies were launched in this time and place. The astronomer Christian Huygens loved to grind and polish lenses for astronomical telescopes and constructed one five meters long. His discoveries with the telescope would by themselves have ensured his place in the history of human accomplishment. Huygens marched in the footsteps of Eratosthenes, he was the first person to measure the size of another planet. Huygens was also the first to speculate that Venus is completely covered with clouds; the first to draw a surface feature on the planet Mars (a vast dark windswept slope called Syrtis Major); and by observing the appearance and disappearance of such features as the planet rotated, the first to determine that the Martian day was, like ours, roughly twenty-four hours long.

Huygens was the first to recognize that Saturn was surrounded by a system of rings which nowhere touches the planet. And he was the discoverer of Titan, the largest moon of Saturn and, as we now know, the largest moon in the solar system – a world of extraordinary interest and promise. Most of these discoveries he made in his twenties. He also thought astrology was nonsense. (Galileo discovered the ring of Saturn, but had no idea what to make of them. Through his early astronomical telescope, they seemed to be two projections symmetrically attached to Saturn, resembling, he said in some bafflement, ears).

Across the sea of space the stars are other suns, but the Earth does move! Image: Colorful mosaics © Megan Jorgensen (Elena)

Christian Huygens did much more. A key problem for marine navigation in this age was the determination of a longitude. Latitude could easily be determined by the stars – the farther south you were, the more southern constellations you could see. But longitude required precise timekeeping. An accurate shipboard clock would tell the time in your home port; the rising and setting of the Sun and stars would specify the local shipboard time; and the difference between the two would yield your longitude. Huygens invented the pendulum clock (its principle had been discovered earlier by Galileo), which was then employed, although not fully successfully, to calculate position in the midst of the great ocean. His efforts introduced an unprecedented accuracy in astronomical and other nautical clocks. He invented the spiral balance spring still used in some watches today; made fundamental contributions to mechanics – e.g., the calculation of centrifugal force, and – from a study of the game of dice, to the theory of probability. He improved the air pump, which was later to revolutionize the mining industry, and the “magic lantern”, the ancestor of the slide projector. He also invented something called the “gunpowder engine” which influenced the development of another machine, the steam engine.

Christian Huygens published Systema Saturnium in 1659, where he showed the correct explanation of the rings of Saturn over the years to the relative geometry of Earth and Saturn changes.

Huygens was delighted that the Copernicus view of the Earth as a planet in motion around the Sun was widely accepted even by the ordinary people in Holland. Indeed, he said, Copernicus was acknowledged by all astronomers except those who “were a bit slow-witted or under the superstitions imposed by merely human authority”. In the Middle Ages, Christian philosphers were fond of arguing that, since the heavens circle the Earth once every day, the can hardly be infinite in extent; and therefor an infinite number of worlds, or even a large number of them (or even one other of them), is impossible.

The discovery that the Earth is turning rather than the sky moving had important implications for the uniqueness of the Earth and the possibility of life elsewhere. Copernicus held that not just the solar system but the entire universe was heliocentric, and Kepler denied that the stars have planetary systems. The first person to make explicit the idea of a large – indeed, an infinite – number of other worlds in orbit about other suns seems to have been Giordano Bruno. But others thought that the plurality of worlds followed immediately from the ideas of Copernicus and Kepler and found themselves aghast. In the early seventeenth century, Robert Merdon contended that the heliocentric hypothesis implied a multitude of other planetary systems, and that this was an argument of the sort called reduction ad absurdum, demonstrating the error of the initial assumption. He wrote, in an argument which may once have seemed withering:

For if the firmament be of such an incomparable bigness, as these Copernical giants will have it ..., so vast and full of innumerable stars, as being infinite in extent… why may we not suppose… those infinite stars visible in the firmament to be so many suns, with particular fixed centers; to have likewise their subordinate planets, as the sun hath his dancing still around him?… And so, in consequence, there are infinite habitable worlds; what hinders?… these and suchlike insolent and bold attempts, prodigious paradoxes, inferences must needs follow, if it once be granted which… Kepler … and others maintain of the Earth’s motion.

But the Earth does move. Merton, if he lived today, would be obliged to deduce “infinite, habitable worlds”. Christian Huygens did not shrink from this conclusion; he embraced it gladly: Across the sea of space the stars are other suns. By analogy with our solar system, Huygens reasoned that those stars should have their own planetary systems and that many of these planets might be inhabited: “Should we allow the planets nothing but vast deserts, and deprive them of all those creature that more plainly bespeak their divine architect, we should sink them below the Earth in beauty and dignity, a thing very unreasonable”.

These ideas were set forth in an extraordinary book bearing the triumphant title The Celestial Worlds Discover’d: Cojectures Concerning the Inhabitants, Plants and Productions of the Worlds in the Planets. Composed shortly before Huygens died in 1690, the work was admired by many, including Czar Peter the Great, who made it the first product of Western science to be published in Russia. The book is in large part about the nature of environments of the planets. Among the figures in the finaly rendered first edition is one in which we see, to scale, the Sun and the giant planets Jupiter and Saturn. They are, comparatively, rather small. There is also an etching of Saturn next to the Earth: Our planet is a tiny circle.

Changes in the Heavens

Changes in the Heavens


Copernicus died in 1543, on the very day that the first copies of his book left the printing press. His opponents soon had much more to contend with. Towards the end of 1572 a new star appeared in the constellation of Cassiopeia. The Danish astronomer Tycho Brahe and other tried to detect its movement relative to the so-called fixed stars, but without success. It clearly belonged to the region of the celestial sphere, a region which, according to Aristotle, was inherently divine, eternal, and unchanging. Aristotle, and the theologians who accepted his world system, were therefore mistaken. As if to drive the point home, a large, bright comet appeared in northern skies in 1577. Tycho Brahe found that it was moving at a distance far beyond the moon and in a very definite path. It changed in appearance night after night, yet moved in celestial regions. How could those region be eternal and unchanging?

Tycho Brahe observing with his large mural quadrant

The new star of 1571 was really an old star which had literally exploded. Its estimated position is now occupied by a weak source of radio emission and a few small, ragged patches of nebulosity. One of these “super new stars”, or supernovae, flared up in 1054, and was mentioned by Chinese analysts of the time. Its remains form an object known as the Crab Nebula, an enormous, expanding, and chaotic mass of gas which emits light, cosmic rays, and radio waves. Yet it is so far away that it looks no more than a small misty patch even in telescopes of moderate size. Its light takes 4,500 years to reach us. The explosion, therefore, occurred not in 1572 but some 3,000 years before the Christian era.

After observing the new star, Tycho Brahe devoted the rest of his life to an accurate determination of the positions and motions of the heavenly bodies. At his observatory at Uraniborg on the island of Hveen, he assembled a princely collection of large measuring instruments of his own design. For 25 years he diligently measured the positions of the stars and used these as reference points for tracing the paths of the five planets. For the first time in many centuries the heavens were studied systematically and in detail, although still within the limits of naked-eye observation.

Breaks with Tradition

Breaks with Tradition


In the first half of the 16th century Nicholaus (Nicolas) Copernicus, a canon of Frauenberg, near the mouth of the Vistula, revived the ideas of two Greek astronomers Philolaus and Aristarchus by stating that the Earth was not necessarily at the centre of the universe. His growing conviction that the geometrical framework of Ptolemy’s system was both inaccurate and unduly involved found its final expression in a book, De Revolutionibus Orbium Coelestrium, printed during the winter of 1542-43. In this he set out the case for thinking of the Earth as a planet. As a planet the Earth rotated on its axis once in 24 hours, thereby producing the apparent daily motion of the sun and stars, and also revolved around the sun once in a year. In his opinion the sun, not the earth, was the true centre of the universe, but since he clung to the old idea that the heavenly bodies moved with uniform motions in circular orbits, his system was still quite complicated.

Nicholaus Copernicus (1473-1543)

The proposed change in viewpoint came as a profound shock to most theologians. The idea that the earth and therefore Man did not occupy a central place in the scheme of things was taken to be a denial of Biblical accuracy and to constitute heresy. Man, it was said, must live at the centre of the universe. Was he not the “apple of God’s eye,” did he not represent the aim and object of all creation, did not the sky revolve above his head and therefor around the earth? Small wonder that Martin Luther referred to Copernicus as “the fool who would overrun the whole science of astronomy”?

Ptolemy’s Almagest

Ptolemy’s Almagest


The last great astronomer of antiquity was Ptolemy, who lived in Alexandria in the second century A.D. He too made a survey of the heavens, being assisted by Hipparchus’s catalogue of stars and the fact that Aratus and others had grouped the stars into forty-eight star pictures or constellations. 

His great book, later known as the Almagest, summarized the main Greek achievements in astronomy and recounted in detail how all the heavenly bodies were supposed to revolve about the earth. The treatment was extremely involved, but it could scarcely have been otherwise. Ptolemy adopted without question the cherished Greek idea that the heavenly bodies moved with uniform motions in circular orbits or combinations of circular orbits. Actually, the moon and planets pursue elliptical orbits, their motions in those orbits are by no means uniform, and we observe them from an earth which is itself a moving body. But the great scope and rigorous treatment of the work ensured success, and it remained the basic text in astronomy until the close of the Middle Ages.

Ptolemy. Renaissance Portrait

The Muslims, to whom we owe most of the star names, studied, commented upon, abridged, and modified the Almagest with great enthusiasm. Many readers, however, were baffled by its geometrical complexity. One classic example was Alfonso X, King of Castille and Leon, surnamed “The Wise”. His reaction was to remark that if God had asked his advice when He created the universe he would have suggested something less complicated. In Western Europe the Church gave almost complete approval to the cosmological ideas of Aristotle and Ptolemy. In fact, these ideas became so sacrosanct that to question them came dangerously near to blasphemy. Not until the 16th century did the first ripples of rebellion against the dogmas of Aristotle disturb the complacency of astronomical and religious thought.

Astronomy Becomes a Science

Astronomy Becomes a Science


After 323 B.C., the year of the death of Alexander the Great, the Centre of Greek learning shifted from Athens to Alexandria. Another change, and a healthy one, was the appearance of a group of men who felt that theory had too greatly out stripped observation. Astronomy depends to a larger extent on the detailed and systematic observation of the movements of the heavenly bodies, a point which earlier Greeks had tended to overlook.

Foremost in the new approach was Aristarchus of Samos, who about 260 B.C. attempted to determine the sizes and distances of the sun and the moon. He also anticipated Copernicus by suggesting that the sun and celestial sphere were at rest while the planets, the earth included, revolved around the sun. But since his scheme was far removed from the earth-centered of commonsense view, it received little or no support.

The Evening Skies. Photo: Elena

The practical approach was also favored by Eratosthenes, a younger contemporary of Aristarchus and head of the great library at Alexandria. He was the first to measure the diameter of the earth by a sound method based on observation of the sun`s height in the sky, and his result, 7,850 miles, was only 50 miles short of the actual diameter.

About 150 B.C. in Alexandria, the Greek astronomer Hipparchus used measuring instruments to determine the places of objects in the sky with an accuracy greater than ever previously obtained. Altogether he recorded the positions of 1,080 stars and grouped them into six magnitudes according to their brightness. By comparing his own observations with others made about 150 years earlier he discovered the precession of the equinoxes, although in this he was preceded by Kiddinu, a Babylonian astronomer.

Scientia. Photo by Elena