What you know and what you can prove aren’t always the same. More than four centuries ago, for example, many astronomers knew that Earth wasn’t the center of the universe — that Earth and the “planets” revolved around the Sun. But proof was elusive. Until Johannes Kepler came along.

Kepler was born 450 years ago today, to a family of modest means in present-day Germany. As a student, he studied theology, astrology, and science. All three of them shaped his view of the cosmos — as a divine creation that could reveal its secrets while guiding the future.

In 1600, Kepler became an assistant to Tycho Brahe, perhaps the best naked-eye skywatcher ever. When Tycho died the following year, Kepler inherited Tycho’s job — and his decades of meticulous observations of the night sky.

It took him several years to work it all out, but Kepler used those records to formulate new ideas about the universe. Those ideas are known today as Kepler’s laws of planetary motion. Among other things, they describe how Earth and the other planets orbit the Sun, and how the Moon orbits Earth.

Later in the century, Isaac Newton used Kepler’s laws to form his own laws about the universe — especially the laws of gravity.

Kepler contributed to science in many other ways. He explained how vision works in the human eye and in the telescope, for example. But his greatest work remains his laws of planetary motion — laws that proved what others only “knew.”

Script by Damond Benningfield

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