Foreword
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.
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