93
See also: Elliptical orbits 50–55 ■ Galileo’s telescope 56–63 ■ Gravitational theory 66–73 ■
The theory of relativity 146–53 ■ Delambre (Directory) 336
URANUS TO NEPTUNE
1784, he turned his attention to
a long-standing question known
as the “great Jupiter-Saturn
inequality.” Laplace showed that
perturbations in the orbits of these
two planets were due to the orbital
resonance of their motions. This
refers to the situation in which the
orbits of two bodies relate to each
other in a ratio of whole numbers.
In the case of Jupiter and Saturn,
Jupiter orbits the sun almost
exactly five times for every two
orbits of Saturn. This means that
their gravitational fields have a
greater effect on each other than
they would for orbits that are not
in resonance.
The nebular hypothesis
Laplace published his work on
the solar system in two influential
books—a popular account called
Exposition du système du monde
and the mathematical Méchanique
celeste. In his Exposition, Laplace
explored the idea that the solar
system developed from a primeval
nebula. Laplace described a
rotating mass of hot gases that
cooled and contracted, breaking
off rings from its outer edge. The
core material formed the sun and
the matter in the rings cooled to
form the planets.
Shortly after Laplace’s death,
his work was translated into English
by the Scottish mathematicianMary Somerville, and this led to
a wide dissemination of his ideas.
Using Laplace’s new theorems,
his fellow countryman Jean
Baptiste Joseph Delambre was
able to produce far more accurate
tables predicting the motions of
Jupiter and Saturn. ■Pierre-Simon Laplace Pierre-Simon Laplace was born^
in Normandy, France, to a minor
landowner. His father intended
him for the Church, and he studied
theology at the University of Caen,
but it was there that he developed
his interest in mathematics. He
gave up any intention of entering
the priesthood and moved to Paris,
where he obtained a teaching
position in the École Militaire.
Here, he taught a young Napoleon
Bonaparte. The post allowed him
time to devote himself to research,
and through the 1780s, he
produced a string of influential
mathematical papers.When Napoleon seized power
in 1799, Laplace became a
member of the senate and
served on many scientific
commissions. He continued
to work on the mathematics
of astronomy until his death,
publishing five volumes on
celestial mechanics.Key works1784 Théorie du movement et de
la figure elliptique des planètes
1786 Exposition du système
du monde
1799–1825 Méchanique célesteOrbital resonance occurs
when the gravity of orbiting
bodies produces a stable
and self-correcting
system. An example
is the orbits of the
neighboring giant
planets Jupiter
and Saturn, whose
orbital periods are
in a ratio of 5:2.JupiterSunSaturnTwo orbitsFive orbits