Mars continues to approach Earth as the Red Planet grows steadily brighter, but on June 28, it will halt its normal eastward motion among the stars and turn back toward the west. A strange change in its nightly wandering that befuddled ancient stargazers.
All of the planets in our solar system exhibit this “retrograde motion” at one time or another. But for the longest time, the ancient astronomers were unable to come up with a satisfactory explanation for it. For one thing, while behaving in this strange manner, Mars will also appear to deviate significantly from its normal course; the retrograde motion will appear to bring it far below its regular orbital track.
In other words, for those of us watching from Earth, during that two-month interval, Mars will appear to travel in a broad loop, measuring about 10 degrees long and 2 1/2 degrees wide. Yet the ancient Greeks staunchly believed that the sun, moon and planets all moved around the Earth in perfect circles. They had a great difficulty in representing and calculating this mysterious loop, and for a long time, they had no adequate explanation for it.
Another problem was trying to explain why Mars sometimes described a loop and other times a zigzag/back-and-forth motion, which resembled the letter “Z” in its path across the sky. In fact, it did just this during the spring of 2016 and will do so again in the late fall of 2022.
The Greeks finally explained away these anomalies by assuming that the planets moved around Earth in smaller “epicycles” — that is, small circles whose centers move along their main orbital circles around Earth, resulting in complex, almost coil-like curves. Unfortunately, the actual observations of the planets never seemed to fit this strange orbital mechanism, ultimately making the Greeks’ explanation utterly useless.
It was not until 1543, when the great Polish astronomer Nicolaus Copernicus(1473-1543) had his lifelong work “De revolutionibus” published, that the secret of the odd retrograde loops were finally revealed. By demoting Earth from its hallowed position at the center of the solar system and replacing it with the sun, Copernicus was able to triumphantly explain the riddle of the apparent “backward motion effect” of the planets.
It’s all an illusion
In fact, it’s the same effect obtained when you pass another car on the highway: Both cars are going in the same direction, but one is moving more slowly. As they pass, the slower car will appear to be moving backward in relation to the faster one. Copernicus applied the same effect to the planets out in space. In the upcoming situation, both Earth and Mars are moving in the same direction around the sun, but the slower one — Mars — appears to move backward compared to the faster one, Earth.
Let’s stress one thing here: Mars is not actually stopping or reversing its orbital path in space! What we are witnessing is merely an illusion based on perspective.After Aug. 28, the movements of Earth and Mars will cancel out the apparent backward motion. Having spent more than half of this year trailing and ultimately catching up to Mars (like race cars “hot lapping” each other), Earth will eventually leave Mars far behind. The rapid increase in brightness for Mars we’re seeing now will be reversed and, consequently, during the latter part of this year, will fade rapidly