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3 Astronomy Around 1875
higher orbital velocity when the planet is closer to the Sun and a longer
orbital period the further they are from the Sun. Subsequently, Isaac Newton (1642–1727) had demonstrated that these properties and laws could be
derived directly from his theory of gravitation. Until the middle of the nineteenth century, great progress was made in the study of the disturbances of
the orbits of the planets by their mutual attraction, which made it possible
to calculate these effects with great accuracy. The high point of this early
modern astronomy was undoubtedly the discovery of the planet Neptune in
1846.
Since antiquity, only the planets that are visible to the naked eye were
known, Mercury up to Saturn. In 1781 William Herschel had accidentally
discovered the planet Uranus during his systematic ‘sweeping’ (surveying)
of the sky. He was a musician who had deserted from the army fleeing
from Hanover to England, and had developed into a very successful amateur
astronomer. The orbit of the new planet could be accurately determined, but
even then deviations were found. This could only be due to the attraction
of a planet even further away. The further away a planet is from the Sun,
the longer it takes to complete an orbit around the Sun. Uranus then would
overtake a planet further out regularly and during that passage the two would
be relatively close to each other; the disturbance of the orbit of one planet by
the other would then be the greatest. Indeed, we now know that Uranus has
‘overtaken’ that eighth planet, Neptune, at the beginning of the nineteenth
century; around 1821/22 they were closest to each other, when they were
on one line as seen from the Sun. Now it should be possible to calculate
from the disturbances of the orbit of Uranus what the orbit of that disturbing
planet would have to be, how massive that planet would be and where it
would be at any given moment in its orbit. No easy task but not impossible
although taking much time.
The Frenchman Urbain Jean Joseph le Verrier (1811–1877) had performed such calculations and had arrived at a prediction of the position of
Neptune in the sky at particular times. Next Johann Gottfried Galle (1812–
1910) found Neptune in Berlin in September 1846 at the position predicted
by le Verrier. The Englishman John Couch Adams (1819–1892) had also
made such calculations (also correctly and predicted a position for Neptune even somewhat earlier), but astronomers of the Royal Observatory in
Greenwich had too little faith in it to check it out. It is ironic that Galileo
Galilei (1564–1642) has actually seen Neptune in his field of view in 1611
during his first telescopic observations, when he discovered the four large
satellites of Jupiter, because Neptune happened to be extremely close to
Jupiter in the sky at that time. However, he did not recognize the planet as
3 Astronomy Around 1875
higher orbital velocity when the planet is closer to the Sun and a longer
orbital period the further they are from the Sun. Subsequently, Isaac Newton (1642–1727) had demonstrated that these properties and laws could be
derived directly from his theory of gravitation. Until the middle of the nineteenth century, great progress was made in the study of the disturbances of
the orbits of the planets by their mutual attraction, which made it possible
to calculate these effects with great accuracy. The high point of this early
modern astronomy was undoubtedly the discovery of the planet Neptune in
1846.
Since antiquity, only the planets that are visible to the naked eye were
known, Mercury up to Saturn. In 1781 William Herschel had accidentally
discovered the planet Uranus during his systematic ‘sweeping’ (surveying)
of the sky. He was a musician who had deserted from the army fleeing
from Hanover to England, and had developed into a very successful amateur
astronomer. The orbit of the new planet could be accurately determined, but
even then deviations were found. This could only be due to the attraction
of a planet even further away. The further away a planet is from the Sun,
the longer it takes to complete an orbit around the Sun. Uranus then would
overtake a planet further out regularly and during that passage the two would
be relatively close to each other; the disturbance of the orbit of one planet by
the other would then be the greatest. Indeed, we now know that Uranus has
‘overtaken’ that eighth planet, Neptune, at the beginning of the nineteenth
century; around 1821/22 they were closest to each other, when they were
on one line as seen from the Sun. Now it should be possible to calculate
from the disturbances of the orbit of Uranus what the orbit of that disturbing
planet would have to be, how massive that planet would be and where it
would be at any given moment in its orbit. No easy task but not impossible
although taking much time.
The Frenchman Urbain Jean Joseph le Verrier (1811–1877) had performed such calculations and had arrived at a prediction of the position of
Neptune in the sky at particular times. Next Johann Gottfried Galle (1812–
1910) found Neptune in Berlin in September 1846 at the position predicted
by le Verrier. The Englishman John Couch Adams (1819–1892) had also
made such calculations (also correctly and predicted a position for Neptune even somewhat earlier), but astronomers of the Royal Observatory in
Greenwich had too little faith in it to check it out. It is ironic that Galileo
Galilei (1564–1642) has actually seen Neptune in his field of view in 1611
during his first telescopic observations, when he discovered the four large
satellites of Jupiter, because Neptune happened to be extremely close to
Jupiter in the sky at that time. However, he did not recognize the planet as