Rick Robinson

Feb 17th 2023

Retrograde Motion: What Happens When Planets Backtrack?


What happens when Mercury is in retrograde? Lifestyle websites might warn you to expect dropped phone calls, airport delays and other strange happenings. They may also suggest it’s a good time to take stock of your personal relationships and brace for bad luck. But, oddly enough, the one thing Mercury’s planetary retrograde has absolutely no effect on whatsoever is Mercury itself.

The periodic retrograde motion of Mercury is not an actual physical motion of the planet — it’s only an optical effect. As Astronomy magazine explains, it’s how Mercury appears to move counter to its usual orbit across the night sky as seen from Earth. Let’s look at what causes this phenomenon and explore the effects of planets in retrograde.

The View From the Merry-Go-Round

When you learn about planets and their orbits from books and websites, they’re often accompanied by diagrams or animated graphics of planets in neat, elliptical orbits. But that’s not what you see when you go outside on a dark, clear night away from city lights and look up at the starry sky.

You don’t see the solar system neatly laid out as if you were looking down at it from a few billion miles above the sun’s north pole. Instead, when you look up at the sky, you see it from Earth’s vantage point inside it, which makes puzzling out its motions a bit like trying to work out the motion of other things on a merry-go-round while you’re riding on it — but even more so because, unlike horses mounted fixedly on a carousel, planets move independently and at varying speeds.

What you see in the night sky are stars forming patterns (the constellations) that do not change from night to night, along with a handful of bright starlike lights that usually twinkle less than their neighbors and shift position compared to the static stars around them. The ancient Greeks dubbed these planetes, or wanderers; we now call them planets.

If you watch the visible planets night after night, they will mostly appear to shift eastward. Every so often, though, a planet’s nightly eastward motion slows to a stop, then reverses. For a period of time — two or three weeks about three times a year in the case of Mercury — the planet shifts westward night by night instead of eastward. This is retrograde motion.

In due course, the retrograde motion also slows to a stop, and the planet resumes its more usual eastward motion against the starry backdrop.

Mysteries of the Calendar

We don’t know when people first recognized the retrograde motion of planets. It must have been long before any form of writing was invented, but we can guess that retrograde motion, like other motions of the night sky, must have seemed like more than just a matter of curiosity.

After all, humans have known that the entire starry sky revolves with the seasons for thousands of years. The stars we see rising after sunset on fall evenings are east of the ones we see rising on summer evenings. By winter, we see stars yet farther east rising at sunset. The night sky is thus a calendar showing the time of year — vital information for early people.

If the motions of the night sky could predict the changes of seasons, as they did, that made them enormously consequential for human life. It’s no wonder, then, that people watched these motions carefully and made their best guesses as to what other consequences they might have for us here on Earth. Astronomy and astrology initially developed together.

Shifting Perspectives

When astrology columns on today’s lifestyle websites discuss what happens when Mercury is in retrograde, their advice comes directly from this very old tradition. Mercury is the fastest-moving planet — not only as to its true orbital speed but also with its apparent motion in the night sky. The Farmers’ Almanac has noted that it was linked from early times to communications and transportation; the Greeks and Romans regarded Mercury as the messenger of the gods.

As for retrograde motion, a planet backtracking from its usual eastward course suggests some sort of disruption or suspension — the equivalent of a person who forgot something and needs to go back for it or someone who is unsure about where to go next. Thus, suggested The Cut, a planet in retrograde provides us an occasion to rethink our perspective on life.

Astrology is not a science: No studies have ever consistently shown that a horoscope can reliably predict our life patterns. But science is not the only tool that people use to make sense of their lives and surroundings. People also find insight in fiction, and, as The Atlantic reported, people’s perspectives on astrology itself are undergoing an interesting shift (though not a retrograde one). So while planets in retrograde may not have any scientific or measurable impact on people, Earth or our fortunes, Mercury in retrograde may have a powerful story to tell about planets from the human perspective. If you draw inspiration from that, more power to you.

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