Johannes Kepler

1571 - 1630
by David F. Coppedge

By anyone’s measure, Johannes Kepler ranks as a gold medalist in the history of science. This great German mathematician and astronomer (contemporary with the King James Bible and the Pilgrims) discovered fundamental laws of nature that have stood the test of time and are still widely used today. He advanced mathematics in science to new heights, including the first use of logarithms for astronomy and the foundation for integral calculus. He made useful inventions. He was a major force in moving science away from its subservience to authority and onto an empirical foundation, and from superstition to mathematical law. He helped mankind understand how the universe works. When the great Isaac Newton expressed that his ability to see farther than others was due to “standing on the shoulders of giants,” he most certainly had Kepler in mind. Yet this humble, devout Christian, from a poor, uneducated home, had a life filled with difficulty. In spite of it, he stands as a consummate example of a Christian doing excellent science from theological motives; Kepler pursued science as a mission from God. In his words, he was merely “thinking God’s thoughts after Him.” Anyone who thinks Christianity is inimical to science should take a close look at the life of this giant of science – and Christian faith.

Kepler is considered the Father of Celestial Mechanics. The story of how he worked for eight years trying to figure out the orbit of Mars and the other planets from the observations of Tycho Brahe is legendary. Kepler was a perfectionist; “close enough” was not good enough.  He started by assuming the common belief that the orbits of the planets must be perfect circles. Moreover, he had a tempting hypothesis of his own, that the ratios of the orbital distances must match the proportions of the regular solids. But it did not quite work. It was Kepler’s genius and integrity that forced him to abandon his pet theory and discover the truth.

After many years of work, and thousands of pages of tedious calculations, he fit the data to the formula for an ellipse, and finally, everything fell into place. This illustrates how in science frequently a fundamental truth lays lurking in the minute details that do not fit the expectations. To an honest scientist, the data must drive the conclusions, and Kepler’s discovery ranks as a seminal point in the history of science. With this finding, he overcame 1500 years of error based on the thinking of Ptolemy, Aristotle and even Copernicus that the heavenly orbits must be perfect circles.

From his discovery, Kepler derived his famous Three Laws of Planetary Motion. These were the first truly scientific laws, based as they were on empirical data and not authority or Aristotelian logic. They were also solidly based in mathematics, and could be used to make predictions. Kepler established precise mathematical relationships describing orbital motion:

  1. The orbits of the planets are ellipses, with the sun at one focus.
  2. The motion of a body is not constant, but speeds up closer to the sun (a line connecting the sun and the planet sweeps out equal areas in equal times).
  3. The farther away a planet is, the slower it moves (the square of the period is proportional to the cube of the semimajor axis).

Newton later explained these relationships in his theory of universal gravitation, but Kepler’s Laws are just as accurate today as when he first formulated them, and even more useful than he could have imagined! Even today, NASA’s Jet Propulsion Laboratory navigates spacecraft around the solar system using Kepler’s Laws, and astronomers routinely speak of Keplerian orbits not only for the solar system but for stars orbiting galaxies, and for galaxies orbiting clusters and superclusters. The whole universe obeys Kepler’s Laws, or as he would have preferred to say, obeys God’s laws that he merely uncovered: he said:

Since we astronomers are priests of the highest God in regard to the book of nature, it befits us to be thoughtful, not of the glory of our minds, but rather, above all else, of the glory of God.

These discoveries alone would be enough to guarantee Kepler membership in the science hall of fame, but there’s much more. Not only was he the Father of Celestial Mechanics, Kepler is also considered the Father of Modern Optics. He advanced the understanding of reflection and refraction and human vision, and produced improvements in eyeglasses for both nearsightedness and farsightedness, and for the telescopes that his colleague Galileo (with whom he corresponded) had first turned toward the heavens. He invented the pinhole camera and designed a gear-driven calculating machine. He investigated weather phenomena and also made other fundamental discoveries about the heavens, such as the rotation of the sun, and the fact that ocean tides are caused primarily by the moon (for which Galileo derided him, but Kepler was proved right). He predicted that trigonometric parallax might be used to measure the distances to the stars. Though the telescopes of his day were too crude to detect the parallax shift, he was right again, and the Hipparcos satellite (1989-1993) used this principle to refine our measurements to thousands of stars. Kepler’s “firsts” make an impressive list of accomplishments.

One would think a man must be the son of a privileged family to rise to such heights, but nothing could be farther from the truth for this scientist, as for other great Christians in this series like Newton, Carver and Faraday. Kepler came from a poor, uneducated family. He was often ill, and lived with no advantages that would have predicted his success. His mother was a flighty woman given to superstition, and his father was a roaming mercenary, frequently off to the battlefield to fight for the highest bidder. At age six, Kepler saw the Great Comet of 1577. In those days, people assumed comets were bad omens, but Kepler was fascinated.

Later, his father bought and operated a low-class inn, and young Johannes was required to do hard labor to help the struggling family business. When given a chance to go to school, Kepler’s genius coupled with diligence advanced him quickly. Devout by nature, he decided he would serve God as a clergyman. He studied for two years in a seminary at the University of Tubingen, receiving training in Latin, Greek, Hebrew, mathematics and the usual Greek philosophy, but there also became acquainted with the newer ideas of Copernicus and those who doubted that the Greeks were the last word in knowledge. It was only when he was pressured to accept a position as a mathematics instructor 500 miles away in Graz that he reluctantly postponed his goal to become a Lutheran minister. Later, he was chosen by the great but eccentric Danish astronomer Tycho Brahe to figure out the problem of the orbit of Mars, and the rest is history.

Artwork by J. Beverly Greene commissioned for this biography. All rights reserved.

In spite of his successes, Kepler’s life was filled with hardship, poverty, political turmoil, false accusations and difficult work. He had to defend his mother who was falsely accused of being a witch. He was forced to move on several occasions due to religious wars or pestilence. He was never paid near what he was worth. He probably never thought of himself as famous. Yet he had an inner joy that would make his imagination soar when he thought of the heavens and how everything worked according to the Creator’s mathematical plan.

A man of passionate imagination as well as scientific rigor, Kepler imagined space travel and speculated about earthlike planets around distant stars. He wrote 80 books, including the first science fiction story, The Dream (about an imaginary flight to the moon), and of course more technical treatises such as the consummate compilation of Tycho’s data using logarithms, The Rudolphine Tables; this work did much to advance the heliocentric theory. His signature work, expressing his philosophy of science, is Harmony of the World in which he saw the heavenly bodies making a kind of celestial “music of the spheres” as the outworking of the mind of God, perfect in geometric harmony. It expressed his belief that the world of nature, the world of man and world of God all fit together into a harmonious system that could be explored by science.



Johannes Kepler had once believed that becoming a clergyman was the only way to serve God and proclaim His truth, but he found that astronomy and mathematics were also a ministry, a way to open windows to the mind of God. Deeply spiritual all his life, he said, “Let also my name perish if only the name of God the Father is elevated.” On November 15, 1630, as he lay dying, he was asked on what did he pin his hope of salvation. Confidently and resolutely, he testified: “Only and alone on the services of Jesus Christ.  In Him is all refuge, all solace and welfare.”

Craters on the moon and Mars are named in Kepler’s honor. NASA’s Kepler spacecraft was launched in March, 2009 and completed its mission in 2018, having found over 3,000 extrasolar planets, all of them obeying Kepler’s Laws of Motion.


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