107
See also: The Milky Way 88–89 ■ Gravitational disturbances 92–93 ■
The theory of relativity 146–53
URANUS TO NEPTUNE
look for the planet. Working with
his assistant Heinrich D’Arrest,
he located an unknown object
within 1° of the predicted position
that same night. Observations on
subsequent nights showed that
the object was moving against the
background of stars and was, indeed,
a planet—one that would later be
named Neptune at Le Verrier’s
suggestion. Galle later gave the
credit for the discovery to Le Verrier.
Independent discovery
At the same time as Le Verrier
was calculating the position
of the unknown planet, British
astronomer John Couch Adams
(1819–92) was also looking at
the cause of the perturbations in
the orbit of Uranus. He arrived at
a similar conclusion to Le Verrier,
completely independently, but his
results were not published until
after Galle had observed the new
planet. There was some controversy
over who should have the credit for
the discovery, but Adams always
acknowledged that Le Verrier had
the better claim.
Galle was not the first person
to observe Neptune. Once the orbit
of Neptune had been worked out,
it was possible to go through old
records and find that others had
already observed it without realizing
it was a planet, including both
Galileo and John Herschel. Later,
Le Verrier used a similar technique
to analyze the orbit of Mercury
and found that perturbations in
its orbit could not be explained
by Newtonian mechanics. He
suggested that this might be due
to the influence of another planet
even closer to the sun, provisionally
named Vulcan. This speculation
ended when Einstein explained
the perturbations using his general
theory of relativity. ■Perturbations in the orbits of planets can be explained by the
gravitational effects of other bodies in the solar system.There may be another
planet beyond Uranus.The orbit of Uranus has
perturbations that cannot
be explained by any
known bodies.Newton’s laws show
where to look for
this planet.Neptune is discovered
very near the place
predicted by the
mathematics.Urbain Le Verrier
Urbain Le Verrier studied
at the École Polytechnique,
near Paris. After graduating,
his initial interests were in
chemistry, before he switched
to astronomy. His astronomical
work was focused on celestial
mechanics—the description
of the movements of the
bodies in the solar system
using mathematics. Le Verrier
obtained a position at the
Paris Observatory and spent
most of his life there, acting as
director from 1854. However,
his management style was
not popular and he was
replaced in 1870. He took
up the position again in 1873
after his successor drowned,
and held it until his own
death in 1877.
Le Verrier spent his early
career building on Pierre-
Simon Laplace’s work on the
stability of the solar system.
He later went on to study
periodic comets before turning
his attention to the puzzle of
Uranus’s orbit.Key work1846 Recherches sur les
Mouvements de la Planète
Herschel (Research on
the Movements of the
Planet Herschel)