Mercury as seen on approach by the Messenger spacecraft during a 2008 flyby of the planet.

We’re in Mercury retrograde. Here’s what that really means.

The planet’s apparent backward motion occurs for a few weeks about every four months. Here’s what’s really happening—and how astrology became a modern phenomenon.

Mercury is seen in an image taken by the NASA MESSENGER probe from a distance of about 17,000 miles. Several times throughout the year, the planet appears to move backwards from our perspective on Earth.
Photograph by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

From a fight with your spouse to a newly-broken part in your car, the planet closest to the sun is often blamed for life’s misfortunes, big and small.

You may hear responsibility placed on “Mercury retrograde,” referring to how the planet appears to move backward in its march across our sky for a few weeks about every four months. This season, it will occur from August 23 to September 14. 

The apparent backward movement of Mercury is an actual astronomical phenomenon, but its connection to happenings on Earth (astrology) is largely refuted as pseudoscience. Still, the idea that Mercury holds power over our communication is popular in the West. 

Retrograde motion has captured sky-gazing humans’ attention for millennia. Today’s astrological interpretation of the planets’ motions trace deep roots to ancient tablets etched by early astronomers.

What happens during Mercury retrograde?

Mercury isn’t actually moving backward in its orbit around the Sun. Retrograde motion is an optical illusion caused by all the planets moving at different speeds from one another. 

It’s kind of like driving on a highway with multiple lanes going the same direction, explains Carolyn Ernst, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory and vice chair of NASA’s Mercury Exploration Assessment Group. If you’re passing a car in another lane that’s going more slowly, they might appear to move backward compared to you, despite going in the same direction, and vice versa. That’s what happens when Mercury laps Earth.

Amidst ancient astronomers’ Earth-centric ideas about the heavens,a celestial body appearing to move backward would’ve presented an eye-catching conundrum. Indeed, the apparent retrograde motion of planets was documented quite early in human history.

First recorded observations of Mercury retrograde

Mercury retrograde was probably first documented by Babylonian astronomers around the 7th century B.C., says Mathieu Ossendrijver, a historian of ancient science, Assyriologist and astrophysicist at the Freie Universität Berlin. 

Those ancient astronomers etched astronomical diaries into clay tablets, describing the motion of the planets in detail—including how Mercury appeared to slow down and loop back on itself. The Babylonian astronomers also created formulas to predict where celestial bodies, including Mercury, would appear in the sky.  

“They had a very clear mathematical understanding of that motion,” Ossendrijver says. 

“In Babylonia, the planets and the stars were viewed as manifestations of gods,” he adds. So any motion or phenomena related to the planets were seen as signs to be interpreted about the fate of “king or country,” he says. The more individual-focused horoscopes came later, around 400 B.C.

Another set of cuneiform tablets detailed how to interpret the motion of celestial bodies. Unfortunately, the tablet interpreting Mercury’s motion is missing, Ossendrijver says, so we don’t know what omens the Babylonians saw in Mercury retrograde. 

We do know the Babylonian name for the planet Mercury “means something like ‘the jumpy one,’” Ossendrijver says. “It’s a planet that jumps back and forth, it’s of course the fastest planet, and so there is some quirkiness about Mercury in the sky, something mercurial, one could say, which the Babylonians already saw in this planet.”

How opinions of astrology in the West changed

The idea that the positions and motion of celestial bodies could predict the fates of a nation, a ruler, a harvest, or an event endured into medieval Europe. 

“You’d have someone really powerful go to an astrologer and say, ‘I want to besiege a castle or attack my enemies, what’s a good time?’” says Nicholas Campion, director of the Sophia Centre for the Study of Cosmology in Culture at the University of Wales Trinity Saint David. 

Mercury in retrograde was believed to impede such endeavors, as well as these astrologers’ divinations. In fact, Campion adds, some astrologers might say they couldn’t read the chart when Mercury was in retrograde.

Still, “no astrological decision would have been taken purely on Mercury retrograde,” Campion says. An astrologer would look at the whole horoscope when answering someone’s question, he says. 

Astrology became popular in Europe as early as the 12th century, Campion says, and drew more enthusiasts after the mechanical printing press was invented in 1439. It had yet to be separated from astronomy as it is today. 

But things started to change within a few centuries, likely due to a combination of political, cultural, and scientific factors. 

In 1543, Nicolaus Copernicus proposed that our planetary system centered around the sun, not the Earth. When Galileo started turning telescopes on the heavens in the early 1600s, the heliocentric model caught on—which, “for many people, made astrology a bit less likely,” Campion says. 

There also may have been a political component eroding interest in astrology, he adds. During the tensions around the English Civil Wars in the mid 1600s, astrology became associated with radical puritans who overthrew the monarchy in 1649. Once the monarchy was restored, all things seen as radical were rolled back. 

By 1700, astrological consultation for personal destinies and the use of personal horoscopes “pretty much disappeared from Europe … and was no longer taken seriously by educated people,” Campion says. Astrology endured only in the publication of monthly or annual almanacs. 

A modern phenomenon

Horoscope astrology began to resurface around the 1920s, Campion says, with regular newspaper columns describing predictions for the 12 zodiac signs. But the popularity of the concept of Mercury retrograde has been a more recent trend, particularly in the last five years, says Jennifer Freed, an astrologer with a PhD in psychology. 

Retrograde is a concept outside of the zodiac signs, so it can appeal to people who are new to astrology, she says. “It’s adjacent to everyone’s experience,” she says. “No one’s left out of the conversation.”

Want to see Mercury go retrograde in the sky?

Because of its speed, Mercury goes retrograde multiple times in an Earth year. After being in retrograde from August 23 to September 14, the planet will next appear to move backward from December 13 to January 1, 2024. 

Keen skywatchers might be able to watch Mercury appear to slow down and then reverse direction during those periods, says Ernst. The trick is to look at where Mercury is in the sky relative to stars or constellations every clear night, and make note of it. Over the nights that pass, those plots will show Mercury appearing to slow down in its progression across the starscape and then loop back on itself, before continuing on. 

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