83
William Parsons, 3rd Earl of Rosse,
took the next big step in the
investigation of nebulae. In the
1840s, he set himself the ambitious
task of constructing the largest
telescope in the world. With it,
he discovered that some nebulae
(which we now know to be
galaxies) have a spiral structure.More planets
Herschel’s discovery of Uranus
aroused fresh interest in the wide
gap in the solar system between
the orbits of Mars and Jupiter.
The regular spacing of the other
planets suggested that there was
an unknown planet in the gap.
It turned out to be occupied not
by a single major planet but by
numerous minor planets, which
William Herschel dubbed “asteroids.”
Italian Giuseppe Piazzi discoveredthe first asteroid, Ceres, in 1801,
as he was observing for a new star
catalog. Three more were located
in the following six years. The next
was not found until 1845, after which
the pace of discovery increased.
Meanwhile, German Ernst
Chladni had correctly concluded
that meteorites reaching Earth are
chunks of rock and metal from space.
Clearly, the solar system contained
a great variety of bodies.The might of mathematics
By contrast to the fortuitous
discovery of Uranus, the discovery
of Neptune was a demonstration
of the power of mathematics. While
astronomers were working with
better telescopes, mathematicians
grappled with the practical
difficulties of applying Newton’s
theory of gravitation to the complexinterplay of gravitational forces
between the larger bodies of the
solar system. The calculations
of German mathematician Carl
Friedrich Gauss in 1801 allowed
Ceres to be relocated, while
between 1799 and 1825, Frenchman
Pierre-Simon Laplace produced
a monumental definitive work
on celestial mechanics.
It soon became evident that
Uranus was not following its
predicted course. The pull of an
unknown planet was suspected.
Building on Laplace’s work,
compatriot Urbain Le Verrier
tackled the problem of predicting
the undiscovered planet’s possible
position. Neptune was duly found
close to where Le Verrier thought
it would be. For the first time,
astronomers now had an idea of the
true extent of the solar system. ■URANUS TO NEPTUNE
1809
1833
1838
1845
1846
1849
German Friedrich Bessel
successfully measures the
stellar parallax of the star
61 Cygni to give a good
approximation of its
distance from Earth.Lord Rosse makes a
drawing of nebula M51,
now called the Whirlpool
galaxy, showing its
spiral structure.Neptune is discovered
very close to the
position predicted
through mathematics
by Urbain Le Verrier.John Herschel begins a
comprehensive survey of the
southern sky to complement
his father’s surveys of the
northern sky.French astronomer
Jean Baptiste
Joseph Delambre
produces a good
estimate of the
speed of light.
US astronomer Benjamin
Apthorp Gould boosts
US astronomy by founding
The Astronomical Journal.