The Neptune File by Tom Standage, AllenLane/ The Penguin Press, 拢12.99,
ISBN 071399472X
ON 13 MARCH 1781, William Herschel spotted something unusual through his
telescope. His first thought was that it was a nebula. Then he saw that this
mysterious body appeared to move against the background of stars: it had to
belong in the Solar System and it must be a comet, he reasoned. In fact, as he
soon realised, it wasn鈥檛 a comet at all but a new planet, the seventh in the
Solar System: Uranus.
About 70 years later, in 1846, the German astronomer Johann Gottfried Galle
also found an intriguing object in the heavens. One autumn night, he watched as
it moved out of step with the stars. He had found the first direct evidence for
the existence of the eighth planet, Neptune.
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These two crucial astronomical discoveries aren鈥檛 merely independent pieces
of good fortune. They are intimately connected, and in The Neptune File
Tom Standage sets out to piece together exactly how one led to the other.
The discovery of Neptune provoked a violent controversy on both sides of the
Channel. It flared up again and again in the following century. The Neptune
Fileshould end the debate once and for all. It weighs up the contributions
of all the players, sorting out the roles of mathematicians John Couch Adams and
Urbain-Jean-Joseph Le Verrier, as well as Galle himself.
Standage weaves into a gripping chronology an impressive amount of
information. Most notable is the lost and rediscovered Neptune File
itself鈥攃orrespondence between Adams and Astronomer Royal George Airy,
who dismissed the suggestion of a planet search, leaving the field to Galle.
Nowadays the planets of our Solar System are so familiar to us, thanks to the
fabulous images sent back by planetary probes and the Hubble Space Telescope,
that the discovery of Neptune may seem a mere collection of entertaining
stories. But it was revolutionary鈥攐ne of the first occasions in the
history of science when theoretical prediction preceded observation.
From the brains of two inspired mathematicians, Adams and Le Verrier, had
come a prediction of the position of a hypothetical planetary body. All that had
to be done to verify this was to look at the right part of the sky. Galle
obliged.
Standage develops an important theme: the scientific method itself, as much
in effect now as then. We still collect data and test a
theory鈥攇ravitation, for example, against them. We still use empirical
models to simplify the problem, and thence make observable predictions that
allow theory and model to be tested. Mathematically, Adams and Le Verrier picked
slightly different paths, but their results were compatible.
The same method applies in current research on extrasolar planets. The
theory鈥檚 the same鈥攇ravity and Kepler鈥檚 laws. Without benefit of direct
visual detection, today鈥檚 planet spotters have nevertheless come up with a test:
they can predict the transit times of certain planets in front of their star.
These transits have been observed at the predicted moment for the star HD
209458, removing the last doubts about the interpretation of the measurement of
a star鈥檚 speed.
The Neptune File will suit a wide range of readers. Its thorough
documentation will satisfy science historians, but Standage鈥檚 clear accounts of
the science behind the story aren鈥檛 bogged down by too much detail. He
illustrates these principles with explanatory drawings that allow non-specialist
readers to grasp what鈥檚 going on. It will please everyone who longs
to learn more about research into planets within the Solar System and
beyond.