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OPINION YEAR OF ASTRONOMY NATURE|Vol 457|1 January 2009 ESSAY Mankind’s place in the Universe Technological developments in astronomy have long helped to answer some of the greatest questions tackled by humanity, recounts Owen Gingerich.

Just over 400 years ago, news Earth-like, rather than a pure ball of crystal- in his A Perfit Description (1576), placed a “hab- swept across Europe of an line aether: the perceived distinction between itacle [home] for the elect” among the stars. astonishing device — two lenses Earth, home of corruption and decay, and the It is not surprising that clerical authorities for within a tube — that almost eternal, aethereal heavens was crumbling. Jupi- the most part resisted the new cosmology. More magically brought distant views ter had no trouble keeping its moons in tow, than this, the Roman Catholic authorities were closer. Its exact origins are lost and everyone agreed that Jupiter was moving. furious that Galileo, a mere amateur theologian, in a mist of controversy, but it is known that Why could a moving Earth not keep its Moon had the audacity to tell them how to interpret one Hans Lipperhey in Middelburg, the Neth- on an invisible tether? Galileo’s skillful polem- scripture. It was clearly a turf battle. Galileo erlands, applied for a patent in October of ics on this matter became full-blown in his was brought to trial in Rome, allowed to plead 1608. His application was turned down on the 1632 Dialogue on the Two Chief World Systems innocent to charges of vehement suspicion of grounds that the unnamed novelty was already — a work that failed to conclusively prove the heresy, but convicted of disobeying orders (in common knowledge. teaching the Copernican cosmology), Seventeen months later a small and sentenced to house arrest for the booklet by an Italian mathemat- remainder of his life. ics professor announced wonderful “New philosophy calls all in doubt,” discoveries made with this newly lamented the poet John Donne. “‘Tis devised spyglass. The title page may all in pieces, all coherence gone.” have implied that the ‘perspicillum’ Galileo’s persuasiveness was helped was Galileo Galilei’s own invention, along by Kepler, whose landmark vol- but he should be forgiven any exag- ume of theoretical astronomy was also geration, for what Galileo had done published in 1609. His aptly named was to turn a popular carnival toy into Astronomia nova or ‘New Astronomy’ a scientific instrument. In December relied heavily on looking at the physi- 1609 he used his spyglass to discern cal causes of planetary motion — a craters, mountains and plains on critical departure from the past, when the Moon. The 400th anniversary of astronomers used strictly geometrical

these astonishing observations sets modelling to explicate the heavens. ORTI DAGLI UFFIZI FLORENCE/A. DEGLI ARCHIVE/GALLERIA ART the stage for what the United Nations Even Kepler’s teacher and mentor, has designated the International Year Michael Maestlin, urged him to for- of Astronomy. get about physics and stick to astron- By January 1610, Galileo had fur- omy (that is, geometry). But Kepler ther found four bright moons of the believed in a physically real cosmos, planet Jupiter (it would be his con- and even ahead of Galileo advocated temporary, Johannes Kepler, who the Sun-centred system. named them ‘satellites’). Before that Heliocentrism as it had come down year was out Galileo had also found from Copernicus, however, was the phases of Venus, proving that it Galileo’s observations of the Moon had far-reaching consequences. flawed. Copernicus used entirely dif- revolved about the Sun. ferent geometrical models for the lati- The implications of such findings were motion of Earth, yet was persuasive enough to tudes of planets than for the longitudes, whereas immense. Although Nicolaus Copernicus’s land him in deep trouble with the Inquisition. for a physically real system, the same model De revolutionibus orbium coelestium (‘On the should work for both coordinates. According Revolutions of the Heavenly Spheres’; 1543) Heavenly vision to Copernicus, the planets moved in circles (the — the work that proposed a Sun-centred or Aristotle had, some two millennia earlier, main ones eccentrically placed with respect to ‘heliocentric’ system — was already nearly seven described a mundane world of earth, air, fire the Sun), and Earth did not move faster when decades old, it was taken only as a manual for and water that was separate from the eternal closest to the Sun. It was Kepler’s requirement computing positions of the planets; by no means purity of the aethereal spheres in the heavens. for plausible physical explanations that drove was it thought to be a physically real description The ecclesiastical vision of a heavy, central him ultimately to postulate an ellipse as the of the cosmos. How ridiculous to think of liv- Earth upon which the human drama played fit basic form of planetary orbits, ironing out these ing on a globe that spun around once every 24 nicely into this Aristotelian cosmos — volca- difficulties. hours! And how could Earth keep the Moon in noes belching out smoke and flames hinted at Alongside Galileo’s telescopic observations, tow if it whirled around the Sun every year? the hellfire below, whereas the realm of God and Kepler’s improvements in planetary theory It was Galileo’s work that made it intellectu- the elect lay beyond the starry firmament. Even eventually brought about general acceptance ally respectable to believe in heliocentrism as a Thomas Digges, the English astronomer who of the Copernican cosmology. In the intro- physical reality. Galileo saw that the Moon was supported the “noble Copernican philosophy” duction to Astronomia nova, Kepler wrote:

“Perhaps there is someone whose faith what significance do rational, is too weak to believe Copernicus observing mortals have in the without offending his piety. Let him wilderness of a near-infinite stay at home and mind his own busi- space-time continuum? This ness. Let him assure himself that he is existential question has been serving God no less than the astrono- simmering for decades and WELLCOME LIB., LONDON WELLCOME mer to whom God has granted the undoubtedly drives our willing- privilege of seeing more clearly with ness to invest taxpayers’ money the eyes of the mind.” in further cosmic explorations. Before and since, astronomi- Today, the electronic revolu- cal devices have been at the heart tion has provided charge-coupled of mankind’s literal search for our devices to replace photographic place in the Universe. It is not an plates that have nearly 50 times inexpensive endeavour. Tycho their efficiency; has made feasible Brahe boasted that his observations the collection and handling of data (which did not involve a telescope in the trillions of bits; and has ena- but rather carefully graduated bled high-speed adaptive optics to naked-eye sightings using quad- compensate for atmospheric varia- rants and other devices) cost the tions, allowing astronomers to take King of Denmark more than a full advantage of large-aperture ton of gold — a huge fortune in Earth-based telescopes. the sixteenth century. Today, tel- The stellar and galactic escopes can cost billions of dol- denizens of the Universe

AKG-IMAGES lars. It could be argued that such can now be catalogued devices are ultimately as useful as never before. That (or useless) to human progress has included, in recent as poetry. But they are funded years, the discovery and because, like the greatest poetry or the build- Fresh views: cataloguing of exoplan- ing of a Gothic cathedral, cosmology is a voyage Thomas Digges’s ets — those beyond our of the human spirit, and as such, a point of per- heliocentric Universe Solar System. sonal or national pride. It is worth a great price (above) and Galileo’s NASA’s Kepler mis- to understand our place in the intricate web of perspicullum. sion, scheduled for time and space. launch in March 2009, mirrors, and the abil- is the first craft designed The farthest reaches ity of photography to explicitly to look for After Galileo’s work and Kepler’s refinements capture images of stars Earth-like exoplanets. — replacing a convex objective lens and con- and nebulae, astrono- Don’t expect radio com- cave eyepiece with two convex lenses, allowing mers finally marched munications from intel- for a wider field of view and accommodating through that portal. In 1859,59 iin a chemical h i l llab- b ligentli life lif to come ffrom one of those planets. crosshairs — the next major leap forward for oratory in Heidelberg, chemist Robert Bunsen But other exciting signals could surely be found. observational astronomy would not come and physicist Gustav Kirchhoff discovered the Today, spectroscopy can be used to spy on the for nearly two centuries. Towards the end of key to unlocking the chemical secrets of the atmospheres of far-away planets, and look for the eighteenth century, William Herschel, Universe via the distinctive spectral lines asso- chemical traces that may hint at signs of life — an inspired musician-turned- ciated with individual elements. even an extremely basic form of life could pro- amateur-astronomer, began “Will we soon Meanwhile, rich philanthropists duce an oxygen signal in a planet’s atmosphere. his seemingly quixotic quest to answer the next poured cash into instruments of Such studies may help in answering the next determine the three-dimensional psyche-shifting discovery, and from the new giant psyche-shifting question: are we alone? structure of the Universe. In the telescopes emerged a sequence of The International Year of Astronomy might process, he discovered a new question: are we consciousness-raising discoveries. well launch the next intellectual revolution in planet — Uranus — an event that alone?” Among them was the immense our understanding of our place in the Universe. changed his status from amateur size of the Milky Way, far beyond Could this have as much of an impact on soci- to professional. The most inventive astrono- anything dreamed of by Herschel. Then came ety as Galileo and Kepler’s entrenchment of the mer of his age, Herschel set on a path to ever- the realization that the Milky Way was but one heliocentric view? Only time will tell. ■ greater light-gathering power by building huge of myriad galaxies stretching beyond by mil- Owen Gingerich is professor emeritus of reflecting telescopes. He ended up counting lions (and even billions) of light years, rushing astronomy and history of science at the Harvard- thousands of stars and discovering hundreds away from each other as if from a cataclysmic Smithsonian Center for Astrophysics in Cambridge, of clusters and nebulae — the gateway to the explosion billions of years ago. Massachusetts, and author of God’s Universe. vast outer Universe beyond the traditional This vast increase in the size and age of the e-mail: [email protected] sphere of naked-eye stars. perceived cosmos set the stage for an angst A century later, thanks to engineering as deep as that caused by the displacement See http://tinyurl.com/57589t for further reading. advances, the discovery of how to silver glass of the ancient human-centred cosmology: See also www.nature.com/astro09.