Nicolaus Copernicus revolutionized our understanding of the universe. He demonstrated that Earth and the other planets orbit the Sun. And he proposed that their orbits were perfect circles.

Decades later, German astronomer Johannes Kepler tried to prove those ideas mathematically. He used observations made by his mentor, Tycho Brahe, to try to plot the orbit of Mars. But he found that Copernicus was off a bit. To explain what’s happening, he devised what are now known as Kepler’s laws of planetary motion.

The first law says the orbits of the planets aren’t circles. Instead, they’re ellipses — like circles that have been flattened a bit. So the distance between a planet and the Sun changes throughout the year.

And the second law says that a planet moves fastest when it’s closest to the Sun, and slowest when it’s farthest.

For a demonstration of those laws, consider an event that takes place tonight: Earth will be closest to the Sun for the entire year — about 1.7 percent closer than the average distance of 93 million miles. We’ll then move farther from the Sun until July.

Because of that close approach, Earth is moving at its fastest right now. And that has an impact on the seasons. Winter in the northern hemisphere is the shortest season — about five days shorter than summer. So if you prefer the warm days of summer, you can thank Kepler’s laws — a nice description of our planet’s motion around the Sun.

Script by Damond Benningfield