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.