Moving Mars

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Moving Mars

Mars is moving at a leisurely pace — slower than at any other time during its almost two-year orbit around the Sun. That’s because it’s farthest from the Sun — 13 million miles farther than average. So the planet is coasting at about 50,000 miles per hour — thousands of miles per hour slower than its average speed.

Neither Mars nor any other planet follows a circular path around the Sun. Instead, their orbits are elliptical — they’re stretched out. And the orbit of Mars is more stretched than most. Its distance from the Sun varies by almost 10 percent in either direction.

Those details were worked out four centuries ago, by Johannes Kepler. At the time, astronomers assumed that the planets all followed circular orbits — perfect shapes. But Mars’s motion didn’t fit that idea.

Kepler pored through years of observations, mostly by his boss, Tycho Brahe. He then spent more years analyzing those observations. From that, he developed several laws of planetary motion. The first law says that Mars and the other planets follow elliptical paths. The second says that a planet moves faster when it’s close to the Sun, and slower when it’s farther away. Since Mars is at its maximum distance today, it’s moving at its slowest — a leisurely pace for the Red Planet.

Mars is a third of the way up the western sky at sunset, and looks like a fairly bright orange star. It’s to the upper left of Venus, the brilliant “evening star.”

Script by Damond Benningfield

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