If you follow Mars across the night sky, you’ll see some odd goings-on. For one thing, it gets brighter and fainter over a period of 26 months. For another, over the same period it stops its normal motion against the sky, moves in reverse for a while, then stops and resumes its usual course. For centuries, that drove scientists loopy.

Until the mid-1500s, most thought Earth was the center of the universe. In 1543, though, Nicolaus Copernicus showed that Earth and the “planets” all orbit the Sun. That explains most of Mars’s behavior. As Earth and Mars follow their own paths around the Sun, our viewing angle changes, so Mars appears to switch directions.

Yet Copernicus assumed the orbits of the planets were perfect circles — an idea that math couldn’t confirm.

The final answer was provided by Johannes Kepler. He pored over decades of observations of Mars. After eight years of effort, he figured it out: Mars and the other planets follow elliptical orbits — like circles that have been stretched out. When it’s close to the Sun, a planet moves faster than when it’s far from the Sun. Kepler’s laws of planetary motion revealed what was happening with Mars — and all the other planets, too.

And Mars is shining at its best this week because it lines up opposite the Sun. It’s in view all night, and shines at its brightest. It’s low in the east at nightfall, and looks like a brilliant orange star.

More about Mars on Thursday.

Script by Damond Benningfield

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