by Archie E. Roy

       I was delighted to be invited by my colleagues Alessandra Celletti and Ettore Perozzi to provide a foreword to their book  Celestial Mechanics : The Waltz of the Planets. Having known them for many years and long admired their work in the subject so many of us love and are fascinated by, I read with great attention and pleasure the text when it arrived. It is a formidable task they have set themselves, to provide a book that describes attempts by successive generations of astronomers from the dawn of history five millennia ago to observe, record and understand the phenomena of the heavens, particularly the intricate and perplexing behaviour of the planets, Sun and Moon. As naked eye astronomy became aided by the telescope and the photographic plate, and since the middle of the twentieth century by instruments launched on spacecraft into circum-Earth orbit or to the Moon and planets and beyond, the discovery of new satellites, scores of them, and ring systems displaying new and initially perplexing behaviour also demanded explanations for that behaviour.

(...)  The popular myth of a scientist is of a rational person who observes, notes, produces a theory or hypothesis, and carefully sets up an experiment to verify or to disprove that theory. If the result of the experiment supports the theory, the scientist has greater faith in his theory, especially if studies by other scientists, replicating his experiment and its results take place and support his findings.  If the result disproves his theory, he without hesitation dutifully discards it or at least modifies it. In this way the body of identified knowledge is expanded, evolving in time to give us a more accurate picture of the world. Ah! If only it were like that.

     Most scientists are formidably expert in their own speciality, are extremely knowledgeable in a wider region and, apart from hobbies, are often as ignorant in everything else as anyone else. One might expect however that their scientific training should give them some advantage in assessing the validity of anything new brought to their attention.  Nevertheless scientists are human too and the modern generation are well aware that they live in a world of politicians, propaganda and spindoctors, a world awash with a torrent of ephemeral frothy and downright worthless media pap for people of limited attention, education and capacity for rational thought. In their own speciality scientists know what they and previous generations of researchers have found. Anything that drastically threatens to challenge the fortress of their hard-won and repeatedly tested and applied consensus of opinion is automatically suspect until supported by replicable experiment. Indeed, the greater the threat, the more reluctant the scientist will be to undertake the required experiments, especially if the person putting forward the new idea is not a respected colleague. In the past, many scientists have demonstrated a hostility to such challenges to seemingly well-established natural laws in their speciality. It is no good the aggrieved pioneer complaining that surely history has shown that the establishment has always spurned or neglected the maverick, the unconventional and the innovator only to accept his discoveries in the end. In this respect the wise words of Marx - not Karl but Groucho! - are relevant.

         "They said Galileo was mad when he claimed the Earth revolved round the Sun - but it does.
         They said Wilbur and Orville Wright were out of their minds when they said men could fly - but they did.
         They said my uncle Waldorf was crazy - and he was as mad as a hatter!'

      In modern times there are also the ever-pressing factors of time and money. In these days when funds for research are difficult to come by, there is enormous pressure from many quarters on the scientist to ensure that his available time is devoted to research projects that are `respectable', grant-attractive and with promise of acceptable, immediately applicable results, improving the status and reputation of the institution that employs him or her.

      In a real sense, all the above is relevant and comes within the science of celestial mechanics. But it is far more than that. In space research it also involves the design and control of the orbits and trajectories within the solar system of the spacecraft we launch together with the ability to know what it requires in rocket hardware to launch them.  Some of its successes in this branch of celestial mechanics, called astrodynamics or astronautics, have been the placing in carefully tailored circum-Earth orbits of the hundreds of multi-purpose satellites for communication, Earth surveillance, observation of the far reaches of the universe; the missions to the Moon, Mercury, Venus, Mars, Jupiter, Saturn and beyond; missions to comets and asteroids; the Mariner and Voyager missions and the spectacularly successful Cassini-Huyghens mission to greatly enlarge our knowledge of Saturn and its system of satellites, particularly Titan.. The astronautical dreams of Tsiolkovski, Hermann Oberth, Walter Hohmann and Werner von Braun became reality.

(...) The authors include accounts of many of the people who have contributed from the earliest times to our understanding of the phenomena of the heavens and the Earth’s place under the celestial sphere. They relate how over four millennia ago in Mesopotamia careful records of eclipses of Sun and Moon, comets, and meteors were kept and attempts made to relate heavenly phenomena to terrestrial events such as famine and flood. We do not know the name of the person, possibly a priest in ancient Babylon, who, going through the astronomical library of clay tablets, discovered that very similar eclipses of the Moon occurred at intervals of 6585 days, a period of time named the Saros. The implications to him must have been staggering. If he could predict a heavenly event, what power it would give the priesthood in predicting terrestrial ones. Did he tell his fellow priests? Or did he, perhaps trembling with excitement, climb the steps of the ziggurat when the next lunar eclipse of that type was due? And only when he had witnessed it, did he reveal his discovery?

     Subsequent pioneers such as Aratus, his poem The Phaenomena, Eudoxus and his sphere, Aristarchus of Samos, Eratosthenes, Hipparchus, discoverer of the precession of the equinoxes, Ptolemy and his epicyclic solar system, their theories and discoveries and the background to their lives are depicted. Later, Kepler, Galileo, Copernicus and Newton appear on the scene. Their lives, background and major contributions to astronomy are clearly given. Running through the accounts of their work is an important thread – motivation.  These people were fascinated by heavenly phenomena, they wanted to understand why things happened, they got a ‘fix’ of supreme satisfaction when they believed their theories accounted for the phenomena. They sought the truth. In a real sense they became people we would recognise. They were scientists.

(...) Mathematical celestial mechanics in fact finds its proper place in this book. Even without their elegant mathematics, the major contributions made by Newton, Lagrange, Poincare, Hamilton and others are clearly described by the authors because of their own expertise in the subject and skill in presentation. Believing also that a picture is worth a thousand words, they have markedly increased the book’s attraction by the choice, number and clarity of the diagrams and illustrations they include. And not the least of the book’s value is the due attention they give to perhaps the hottest astronomical topic of the twenty-first century, the continuing discovery of planetary systems of other stars and the search for extraterrestrial life not only in our own solar system but also elsewhere in the universe. Giordano Bruno’s heresy about the plurality of worlds will even receive its ultimate verification this century if life elsewhere is found. It would be a discovery equally as momentous in its implications for humanity as Darwin’s theory of evolution.

      I enjoyed this book. It is fresh and attractively written in its presentation of humanity’s long-lasting love affair with the universe and I thank Alessandra and Ettore again for inviting me to provide the foreword.

Archie E. Roy.

                                                                                 Professor Emeritus of Astronomy,
                                                                                 Honorary Senior Research fellow,
                                                                           Department of Physics and Astronomy,
                                                                                   Glasgow University, Scotland.

find @



Hosted by