Science Milestones: A New Astronomy with Johannes Kepler

Each month, I like to share a post celebrating the accomplishments of a scientist whose discoveries and advancements have made a significant difference in our lives. To honor the work of these amazing people, I provide a little peak into their life and share an unschool-style learning guides or unit study to guide you and your children on a path of discovery.

This month, I chose to honor the Johannes Kepler, who lived in an era when there was no clear distinction between astronomy and astrology. There was, however, a strong division between astronomy (a branch of mathematics within the liberal arts) and physics (a branch of natural philosophy).

Science Milestones: A New Astronomy with Johannes Kepler @EvaVarga.netJohannes Kepler

In 1596, the German astronomer published his first important work on astronomy, Mysterium Cosmographicum (The Cosmographic Mystery). As well as defending the heliocentric model of the universe previously proposed by Copernicus in 1543.

Kepler explained the orbits of the known planets around the Sun in geometric terms in an attempt to unravel “God’s mysterious plan of the universe.” To do this, he dow upon the classical notion of the “harmony of the spheres” which he linked to the five Platonic solids – octahedron, icosahedron, dodecahedron, tetrahedron, and cube.

Science Milestones: A New Astronomy with Johannes Kepler

The Platonic solids, when inscribed in spheres and nested inside one another in order, correspond to the orbits of the planets Mercury, Venus, Earth, Mars, Jupiter, and Saturn.

In 1619, he published Harmonices Mundi (The Harmony of the World) wherein he stated his third law of planetary motion. He described the relationship between a planet’s distance from the Sun and the time taken to orbit around it as well as the speed of the planet at any time in that orbit.


Science Milestones: Johannes KeplerKepler was born in the small town of Weil der Stadt in the Swabia region of Germany and moved to nearby Leonberg with his parents in 1576. His father was a mercenary soldier and his mother, the daughter of an innkeeper. Johannes was their first child.

When Johannes was just five, his father left home for the last time and is believed to have died in the war in the Netherlands. As a child, Kepler lived with his mother in his grandfather’s inn. He tells us that he used to help by serving in the inn.

Kepler’s early education was in a local school and then at a nearby seminary. Intending to be ordained he went on to enroll at the University of Tübingen, a bastion of Lutheran orthodoxy.

Throughout his life, Kepler was a profoundly religious man. All his writings contain numerous references to God, and he saw his work as a fulfilment of his Christian duty to understand the works of God.

At Tübingen Kepler was taught astronomy by one of the leading astronomers of the day, Michael Mästlin. The curriculum was of course, geocentric astronomy, in which all seven planets – Moon, Mercury, Venus, Sun, Mars, Jupiter and Saturn – moved around the Earth, their positions against the fixed stars being calculated by combining circular motions.

This system was more or less in accord with current Aristotelian notions of physics, though there were certain difficulties. However, it seems that on the whole astronomers were content to carry on calculating positions of planets and leave it to natural philosophers to worry about whether the mathematical models corresponded to physical mechanisms. Kepler did not take this attitude. His earliest published work, Mysterium Cosmographicum, proposed to consider the actual paths of the planets, not the circles used to construct them.

 “I am satisfied…to guard the gates of the temple in which Copernicus makes sacrifices at the high altar.” ~ Johannes Kepler

Kepler was one of the few pupils to whom Mästlin chose to teach more advanced astronomy by introducing them to the new, heliocentric cosmological system of Copernicus. Kepler seems to have accepted almost instantly that the Copernican system was physically true.

Soon after moving to Regensburg in 1630, he became seriously ill with fever and on November 15 he died.

Bring it Home

What are Kepler’s three laws of planetary motion? How were his ideas viewed by his contemporaries?

Learn more about star polyhedra, discovered by Kepler in 1619 and prominently featured in the architecture of European churches.

Build models of the five Platonic solids; consider The Finnish Craft of Himmeli or Paper Models of Polyhedra.

Research the epitaph inscribed on his gravestone (sadly swept away in the Thirty Years War):

I used to measure the heavens,
now I shall measure the shadows of the earth.
Although my soul was from heaven,
the shadow of my body lies here.


Science Milestones

Visit my Science Milestones page to learn more about scientists whose discoveries and advancements have made a significant difference in our lives or who have advanced our understanding of the world around us.

Interested in learning about others who were born in the month of January? Hop over to Birthday Lessons in December to read posts by other iHomeschool Network bloggers.