Astronomic icon: Remembering Johannes Kepler’s ‘interstellar’ legacy

Johannes Kepler’s legacy lives on all around us. If Kepler were alive today, he would be celebrating his 450th birthday. He was one of those early thinkers who revolutionised science and the way we see and understand the universe — the natural world and life itself. Kepler was an astronomer and mathematician. 

He stands next to giants like Copernicus, Galileo, and Newton. And today’s science stands on their shoulders.

Kepler was born on December 27, 1571, near what is now Stuttgart in southern Germany. He is best known for his discovery of three laws of planetary motion. Presented between 1609 and 1619, those laws describe how the planets orbit around our sun. 

Living at a time when there was a strong divide between astronomy and physics, Kepler wanted to bring the two disciplines together. In doing so, he transformed scientific thought. It all started with Kepler’s discovery that Mars orbited the sun in an ellipse — an oval shape.

That first discovery led Kepler to then realise that all the planets moved at different speeds around the sun in an elliptical orbit. 

This improved on an earlier heliocentric theory, proposed by a Polish mathematician and astronomer Nicolaus Copernicus, who had theorised that the planets orbited the sun in a circular movement.

Kepler’s laws of planetary motion were essential for Isaac Newton’s law of gravitation in the 1680s. Newton’s law says that all objects — or the particles that make up objects — attract each other with a gravitational force. And that explains why planets orbit around the sun in the first place. 

Kepler’s laws are helpful when it comes to our understanding of the movement of natural objects. They help us understand stellar systems and extrasolar planets, which are outside our solar system. 

They are also used in the design of rocket trajectories and how we have satellites orbit our planet today. Satellites can be farther or nearer to us, depending on where they are on their orbit — that’s the nature of an elliptical orbit.

And that’s important to know when, for instance, you are planning when and where you can take images of Earth — or when it’s most efficient to send data from one place on Earth to another via satellite. 

Kepler was born into a time when the scientific community worked within the confines of religion and the church. It wasn’t always an easy match between science and religion, and many early philosophers and scientists paid the price.

In Kepler’s case, religion was a positive influence. He avoided calling his discoveries about planetary motion “laws” and instead considered them “celestial harmonies” that reflected God’s design for the universe. All schooling at the time was controlled by church institutions, both Roman Catholic and Protestant. Kepler was raised in a Lutheran family. He received a scholarship through the church and that started him on his scientific journey. 

He attended a seminary at the University of Tübingen from 1589.

People tended to graduate from these schools to become teachers or church ministers — Kepler had initially planned to become a theologian. That was until he studied under his mentor, Michael Mästlin. What Kepler’s story shows us, however, is how science evolves. 

It is in constant flux and movement, discovery and rediscovery. It reminds us how scientific thought exists in the context of its times and the lives of its thinkers.