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The history of the zodiac

There’s a predictable moment in the year when the news cycle slows and the same types of articles fill the blogosphere:

Did You Know That Your Astrology Sign Is Wrong?

Have You Heard of the 13th Sign?

Why You’re No Longer a Scorpio!

These relentless headlines are designed to attract clicks, upend mainstream knowledge about astrology, and cast doubt on the ancient practice.

There’s just one problem: These aspirational gotchas aren’t revelations at all.

Many of the articles hinge their arguments on a phenomenon called “the precession of the equinoxes” — aka old news repackaged as clickbait. But astrologers aren’t the ones who are behind on the state of the sky; the journalists are. By about 2,000 years. So before you mournfully fold up your “Virgo 4 Lyfe” T-shirt, let’s break down exactly what these articles get wrong — and right — about how astrology works.

Time to get technical

First, we have to understand the concept of the ecliptic. The ecliptic is the path that the Sun appears to carve through the sky over the course of the year. It’s like a celestial superhighway where the Sun, Moon, and planets appear to travel from our vantage point on Earth. “From our vantage point” is a key phrase here: We’re writing horoscopes for Earthlings, generally, so we interpret the sky from the Earth’s perspective.

So as Sol, Mercury, Venus, and the rest move along this strip of sky-road at varying speeds, their journeys have a stable backdrop: the fixed stars. Unlike the planets, the relative positions of these stars don’t appear to change. Their stability helps us locate the planets in their journey. The stars that sparkle along the ecliptic belong to the zodiac family of constellations, groups of fixed stars identified by familiar names such as Aries, Taurus, Gemini, and so forth. From our perspective, Sol appears to take one Earth year to pass through all 12 of these constellations.

Would-be debunkers claim that your Sun sign is indicated by the constellation behind Sol at the moment of your birth. If the constellation Scorpius lurks in the background of the Sun when you are born, news outlets explain, you are a Scorpio. These writers add that, because of a phenomenon called the precession of the equinoxes, the Sun no longer aligns with the same constellations it did when the first astrologers observed it 2,000 years ago. So that means astrology must be all hogwash, right?

Wrong.

To help you understand why, we have to explain the phenomenon of precession.

Precession of the equinoxes

It’s common knowledge that the Earth rotates on its axis once every 24 hours. That’s how we get day and night. But the Earth’s axis itself also rotates, like a slowly spinning top, gradually completing its cycle approximately once every 26,000 years. This secondary rotation creates a tilt, often referred to as a “wobble” — in more scientific terms, a precession.

Because of this imperceptible wobble, the constellation in which Sol rises on the equinox changes over time. It drifts by about one degree every 72 years — and about one sign every two millennia. Hence the name: “the precession of the equinoxes.” The relative positions of the fixed stars don’t change, but the Sun won’t always appear in the same place among the fixed stars on a given date. So if Sol no longer aligns with the Ram constellation on March 21st, the critics argue, it might be time to put away your trademark Aries necklace and embrace your new identity as a Pisces. Reasonable, right?

It would be — if it had anything to do with the past 2,000 years of Western astrology. What these media outlets get wrong is that astrologers have been well aware of precession and have developed multiple approaches to dealing with its effects.

Two ways to map the stars

To address the question of precession, the ancients established two distinct zodiacs. One is the sidereal zodiac, the dominant system used in India today. The other is the tropical zodiac, now the most common in North America and Europe.

By the 5th century BCE, the Mesopotamian astronomer-astrologers standardized the signs of the zodiac as 12 equal, 30-degree segments of the sky, independent of the constellations themselves. Over time, astrologers started to call this system the sidereal zodiac (from the Latin term sidereus, “of the stars or constellations”). This was the move that solidified astrology as a primarily symbolic practice, not a purely empirical one, since it doesn’t reflect the exact positions of the stars in the sky.

Think of it this way: The night sky seems boundless, but what the human mind can conceptualize is not. Thanks to the ancient Mesopotamians, your astrological chart is evenly divided into 12 portions, which represent 12 distinct signs. But in the heavens, the constellations aren’t so orderly. The stars of Virgo, for example, sprawl across a wide section of the ecliptic, whereas other constellations, such as Cancer, occupy a relatively narrow slice.

But sidereal astrologers do take into account the impact of precession and adjust the location of the signs to roughly align with the constellations. In other words, those so-called “new signs” in the tabloids are already used by sidereal astrologers across the world. To be clear: The system is still symbolic. Sidereal astrologers still pretend that the constellation Virgo isn’t taking up a disproportionate share of ecliptic real estate. But they adjust the degrees to account for the past 2,000 years of “wobble.”

So that’s one approach.

The second approach is to pin the astrology to something that doesn’t change: the equinox. The equinoxes are the two days each year when there is a perfect balance of daylight and darkness — no matter where you are on Earth, and no matter when in history. Two millennia ago, when ancient astrologers were getting it all down in writing, the Sun entered the constellation Aries on the Northern Hemisphere’s vernal equinox. So 0° Aries became the first degree of the tropical zodiac.

The ancient Greek astronomer Hipparchus, who discovered the phenomenon of precession, used the tropical zodiac system to stabilize his calculations. Hipparchus and other astronomers knew that, eventually, a different constellation would be Sol’s backdrop on the equinox. But that didn’t bother them, since the zodiac has always been a symbolic representation of the sky. For thousands of years, the tropical zodiac has reflected the steady rhythm of the seasons, not the slow drift of the constellations.

Which zodiac is more accurate?

Around the first century BCE, the sidereal and tropical zodiacs were roughly aligned, and the Sun would begin to rise in Aries on the first day of spring in the Northern Hemisphere. Both zodiac systems were in use, so it can be difficult to differentiate between the two in early astrological texts. But as the effects of precession became more evident, so did the unique strengths of each system. And in the second century BCE, Claudius Ptolemy — the famed mathematician, astronomer, astrologer, and geographer — decisively favored the tropical zodiac over the sidereal in his writings.

So which system is better? Neither. Each system imparts uniquely valuable wisdom, and what works best for you is a matter of personal preference. But it’s important to note that astrologers were aware of the Earth’s wobble thousands of years ago, and they developed both zodiac systems in accordance with that knowledge.

Another crucial point: Astrology may be symbolic, but that doesn’t mean it’s false. There are many fields in the world — including poetry, psychoanalysis, and spirituality — whose secrets and powers can’t be explained in a lab report. Astrology’s relevance has extended across continental divides and millennia of profound cultural upheaval — and for good reason. As important as scientific inquiry is, it doesn’t always line up with the art of astrology. And it doesn’t need to; both disciplines are still valid. But it would be nice if the folks trotting out these tired headlines were to do a bit more research on their subject matter.