3
Astronomy Around 1875
O, telescope, instrument of much knowledge,
more precious than any scepter, is not he who holds thee
in his hand made king and lord of the works of God?
Johannes Kepler (1571–1630)
I have looked further into space than ever a human being
did before me. I have observed stars of which the light,
it can be proved, must take two million years to reach the Earth.
William Herschel [1].
3.1 Astronomy of the Solar System
A little bit of astronomical background is needed for a good understanding
of Kapteyn’s work and appreciation of its significance. I start with the Solar
System.
Our Solar System consists of eight planets, from the Sun first the ‘terrestrial’ planets with a solid surface, Mercury, Venus, Earth and Mars, and
further out the ‘gas giants’ Jupiter, Saturn, Uranus 1 and Neptune. The properties of their orbits were described around the beginning of the seventeenth
century by Johannes Kepler (1571–1630) in the form of his three laws,
which specify that they are elliptical with the Sun in a focus and with a
1 Uranus should be pronounced with the emphasis on the first syllable ‘U’.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Switzerland AG 2021
P. C. van der Kruit, Pioneer of Galactic Astronomy: A Biography of Jacobus C. Kapteyn,
Springer Biographies, https://doi.org/10.1007/978-3-030-55423-1_3
27
Astronomy Around 1875
O, telescope, instrument of much knowledge,
more precious than any scepter, is not he who holds thee
in his hand made king and lord of the works of God?
Johannes Kepler (1571–1630)
I have looked further into space than ever a human being
did before me. I have observed stars of which the light,
it can be proved, must take two million years to reach the Earth.
William Herschel [1].
3.1 Astronomy of the Solar System
A little bit of astronomical background is needed for a good understanding
of Kapteyn’s work and appreciation of its significance. I start with the Solar
System.
Our Solar System consists of eight planets, from the Sun first the ‘terrestrial’ planets with a solid surface, Mercury, Venus, Earth and Mars, and
further out the ‘gas giants’ Jupiter, Saturn, Uranus 1 and Neptune. The properties of their orbits were described around the beginning of the seventeenth
century by Johannes Kepler (1571–1630) in the form of his three laws,
which specify that they are elliptical with the Sun in a focus and with a
1 Uranus should be pronounced with the emphasis on the first syllable ‘U’.
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Switzerland AG 2021
P. C. van der Kruit, Pioneer of Galactic Astronomy: A Biography of Jacobus C. Kapteyn,
Springer Biographies, https://doi.org/10.1007/978-3-030-55423-1_3
27