Kepler and the planetary harmony – Part I

There are multiple stories of perseverance and hard work in science history, on how even under adverse conditions, curiosity and the desire to find answers is stronger than any adversity; One interesting example is that of Johannes Kepler.

Kepler is one of the most important figures in Astronomy, and his contribution in this field was fundamental to later complement the work of other scientific personalities such as Huygens, Halley and Newton.


Complicated life

Kepler suffered several misfortunes during his life; in his childhood he was the victim of smallpox, which caused him permanent damage such as poor vision and a hand motor disability, which limited his work in experimental side of the astronomy, a passion he discovered at a young age. Kepler had the opportunity to see “the great comet” of 1577, a non-periodic comment that was seen in that year. Then at the age of nine he was able to witness a lunar eclipse, which sparked his interest in science and astronomy.

Kepler lived at a time when religious institutions still ruled and were the dominant power; and where the distinction between science and esotericism was not yet well delimited; and because of this his study included astronomy and astrology, learning about the incorrect Ptolemaic system; the solar system model accepted by the dominant religious institutions at that time, where the Earth was positioned in the center and the planets and the Sun orbit around it. But he also learned about the Copernicus model, which correctly describes how the solar system is constituted. As was usual at that time, higher education institutions were also controlled by the cleric, and Kepler, even when tried to become a minister, was eventually recommended to become a professor in Mathematics and Astronomy.

His misfortunes continued when after his marriage, he lost her first two children (this, although was not uncommon, was still tragic). Later he had three more children, but at early age, he lost two of them due the smallpox; and later he had the loss of his wife because of a severe infection; he also later became practically a refugee, having to move to Prague after the religious instability generated after the death of Emperor Rudolph.



Kepler began his research on the mechanics of the planet’s orbits in the solar system; but with the influence of astrology his first attempts failed, as he attempted to define this as a model of concentric polygons, based on platonic solids, trying to give a “divine explanation” based on a geometric plan to the mechanics of planet’s movement, model that he presented in his book Mysterium Cosmographicum.

Kepler platonic solids (

Kepler platonic solids (

Later, seeking accreditation of his work by the scientific community at that time, he maintained communications with different figures of the time, among them Tycho Brahe, another very important cosmologist, who kept very detailed records of observations of the movement of the planets, records that he guarded jealously. The professional relationship of Kepler and Tycho Brahe was becoming very close, but it was always very complicated, Kepler finally and after complicated negotiations agreed to work with him, but he was only working as a clerk doing general calculations. Tycho was very mistrusted of the discoveries that could be achieved through his observations, and for that reason presented to Kepler only fragments of his observations to avoid this possibility, recognizing Kepler’s skill and expertise; situation that Kepler did not find encouraging at all.

Johannes Kepler & Tycho Brahe (

Johannes Kepler & Tycho Brahe (

Tycho Brahe died in 1601, and Kepler obtained the position he held as Imperial Mathematician for the emperor Rudolph the second, and with this position he finally had access to the records and data accumulated by Tycho; and with them he finally had the means to restart his work on the mechanics of the planets, these became the most productive years of his career.


Kepler Laws

The culmination of this work was presented in 1605 (although it was finally published in 1609), in his book “Astronomy Nova“, where he presented two of the now known as Kepler laws that state the following:

I. Planets move in elliptic orbits, with the Sun located in one the foci.
II. The radius vector describes equal areas in equal times.

Kepler continued analyzing the data for several years, trying to find a new revelation, and it was until the year 1618, when, as he relates it, “in a moment of inspiration, it appeared in my mind“, having the epiphany that would become his third law.

III. For any planet, the square of its orbital period is directly proportional to its to the cube of the major semi-axe of its elliptic orbit.

After finishing his work, he had to defend it quite fiercely, as it was not fully accepted by the so-called scientists of the time, basing their disputes on astrological approaches; this discussion caused Kepler to publish Tertius Interveniens (Interventions of third parties), where, even though it did not discredit astrology altogether; he put it in a different category of non-scientific studies calling it the “dung from which occasionally a seed or even a gold nugget can be found“.

Kepler continued his work for several years, this including the publication of the “Rudophine tables“, a catalog of stars and planets, named in memory of Emperor Rudolf II, a work that was considered his greatest contribution at that time.

In this article I will not delve into what these laws represent, and what is their meaning to explain the movement of the planets. This topic is very interesting, and I do not want to miss the opportunity to present this information with the detail it deserves and to note what Kepler laws represent and their understanding of the planet’s movement; Kepler’s work of and his three laws were key in the work of Newton, whose laws are a generalization of Kepler’s laws. They are also indirectly related to Einstein’s work, to explain his general theory of relativity.

Kepler can certainly be considered a pioneer in his field, and one of the first to initiate the separation between religious institutions and science, a fundamental step in modern science.


Alex, ScienceKindle


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