Sky & Telescope - September 2022 - 38

Solar System History
the effect of making further correspondence between the two
astronomers impossible for nearly a year.
As for the battles over credit for Neptune's discovery,
research by historian Robert W. Smith and others reveals
that in the 1840s, scientists were already intensely focused
on working out ground rules for establishing what, exactly,
constitutes a discovery. Was Neptune " discovered " when
its existence was mathematically predicted, or only after its
presence was verified through a telescope? Were pre-discovery
sightings actually themselves discoveries? The idea was
emerging that there must be some connection between scientific
merit, priority, and publication, but at that time there
was no consensus.
A " Happy Accident, " Indeed
Amongst everything else surrounding the discovery of Neptune,
was the question of this event signifying the moment
in which (in the words of the great historian of 19th-century
astronomy Agnes Mary Clerke) " the last lingering doubts
as to the absolute exactness of the Newtonian Law were
dissipated " ? Despite the apparent promise of the inverseperturbation
approach pioneered by Le Verrier and Adams,
the mathematical feat was never again successfully repeated,
though not for lack of trying. This includes Percival Lowell's
well-known, fruitless attempts in the late 19th and early 20th
1850
1840
1830
1830
1850
1840
Sun
1810
1800
1800
1820
1820
1810
COINCIDENTAL POSITIONS The orbits predicted by Adams and Le
Verrier for a hypothetical outer planet diverged not only from each other,
but also from the actual orbit of Neptune. Remarkably, however, all the
orbits approximately coincided for several decades in the early 19th
century - just as the hunt for Neptune was underway.
centuries to find a " Planet X " more distant than Neptune.
In 1892, mathematician Henri Poincaré published his
monumental work Les Méthodes Nouvelles de la Mécanique
Céleste. It revolutionized understanding and methodology
of celestial mechanics, recasting calculations in terms of
statistical probabilities, thus sounding the death knell of the
Newtonian deterministic clockwork universe. Indeed, because
of gravitational resonances among planetary orbits, computational
models reveal that planetary positions and velocities
fall not only into regions of regular predictable behavior, but
also into regions of chaotic, unpredictable behavior.
So was the discovery of Neptune indeed just a happy
accident? Modern mathematical analysis of Uranus reveals
there were actually two solutions to the inverse-perturbation
problem. " One solution was the one found by Adams and Le
Verrier, " concluded Sheehan and mathematician Kenneth
Young, " the other is displaced 180 degrees opposite. The fact
that Adams and Le Verrier found the correct solution (the
one actually occupied by the planet at the time) would seem
to be rather fortuitous. "
So, the solar system's outermost major planet was found -
not only through the efforts of a remarkable group of astronomers,
but also because of extraordinary good fortune.
PLANET CATCHER Galle and d'Arrest used this magnificent, 9.6-inch
Fraunhofer refractor to locate Neptune using positions calculated by
Le Verrier. They found the planet after just one hour of searching, slightly
more than 1° from the predicted position.
38 SEPTEMBER 2022 * SKY & TELESCOPE
¢ Contributing Editor TRUDY E. BELL is coeditor of Neptune:
From Grand Discovery to a World Revealed (Springer, 2021).
She wishes to thank historians Roger Hutchins, Carolyn Kennett,
James Lequeux, Robert W. Smith, William Sheehan, and
Brian Sheen for their helpful input to this article.
U
N
c
l
a
c
r
p
e
u
c
l
a
t
a
l
l
u
n
e
d
d
e
u
b
s
b
y
y
n
u
e
t
t
a
r
O
i
b
O
c
t
r
b
a
t
i
L
d
e
a
V
e
s
r
r
i
e
r
A
m
BERLIN OBSERVATORY TELESCOPE: DEUTSCHES MUSEUM; ORBIT: GREGG DINDERMAN / S&T;
SOURCE: WILLIAM SHEEHAN / PUBLIC DOMAIN
Sky & Telescope - September 2022

Table of Contents for the Digital Edition of Sky & Telescope - September 2022
