Articles periodically circulate online claiming that astronomical observations, sometimes referencing NASA, have “changed the zodiac” or invalidated astrological signs. These stories usually rely on two astronomical facts: the shifting position of constellations over time and the existence of a “13th sign,” Ophiuchus.
This often leads to confusion about whether astrological signs are now “wrong.” The discrepancy, however, comes from a fundamental misunderstanding between two different systems: scientific astronomy and the system of tropical astrology.
Both use the same names (e.g., Aries, Pisces) to describe different things: physical constellations in space versus a symbolic calendar based on Earth’s seasons.
Astronomy is a science, with precession and 13 constellations
From a scientific perspective, astronomers are describing well-established facts.
The first fact is precession. Earth has a slight “wobble” as it spins on its axis, a cycle that takes roughly 26,000 years to complete. When the zodiac system was developed over 2,000 years ago, the constellations and the seasonal signs roughly aligned. Around the spring equinox, the Sun appeared “in” the constellation Aries.
Because of precession, Earth’s axis has since shifted. Today, at the spring equinox, the Sun is actually in front of the constellation Pisces.
The second fact is that the Sun’s path – the ecliptic – passes through 13 constellations, not 12. Astronomers recognize this 13th constellation as Ophiuchus (the serpent-bearer). The Babylonians were aware of it but likely left it out to keep a clean 12-part system that matched their 12-month calendar.
From a purely astronomical standpoint, if “signs” were defined strictly by the current positions and widths of these constellations, most people would indeed have a different sign.
Tropical astrology is a symbolic, seasonal system with 12 signs
The apparent conflict disappears once you look at how Western astrology actually works. This system, known as tropical astrology, is not based on the physical constellations. It is a symbolic framework based on the seasons.
In the tropical system, the zodiac is divided into 12 equal 30-degree segments. The starting point, 0° Aries, is defined as the exact moment of the spring equinox (the first day of spring).
Consequently, 0° Cancer is the summer solstice, 0° Libra is the autumn equinox, and 0° Capricorn is the winter solstice.
A person’s “sign” is just the label for whichever 30-degree segment the Sun occupied at their time of birth.
Because the tropical zodiac is defined by the equinoxes and solstices, it stays aligned with Earth’s seasons. Precession shifts the background constellations, but in this framework their positions are not a factor. The spring equinox always marks the start of Aries, regardless of which stars lie behind the Sun.
Understanding the key distinction
The confusion arises because these two systems use overlapping terminology to describe different things:
- Constellations (Astronomy, science): Physical groupings of stars in the sky. They have different sizes and shapes. The Sun passes through 13 of them along the ecliptic.
- Signs (Tropical Astrology, symbolic belief): Twelve equal, symbolic divisions of the sky used as a celestial calendar fixed to Earth’s seasons.
There is another, less common system called sidereal astrology, which ties the zodiac more closely to the constellations and explicitly accounts for precession. In a person’s sidereal sign will often be different from their tropical sign.
However, in the Western (tropical) system, the zodiac signs remain consistent and are unaffected by changes in the apparent positions of the stars or by the Ophiuchus constellation, because the system was never based on the physical star patterns in the first place.
Sources
Britannica – precession of the equinoxes – 2023
This source provides a scientific definition of precession as the wobble in Earth’s axis, explaining the mechanics behind this long-term cycle.
Space.com – What’s your zodiac sign? (It may not be what you think it is) – 2022
This article explains the astronomical facts, clarifying that the Sun is currently in front of Pisces during the spring equinox due to precession.
EarthSky – Is Ophiuchus the 13th constellation of the zodiac? – 2025
This source confirms the astronomical position of Ophiuchus as the 13th constellation that the Sun passes through on the ecliptic.
Astrology Zone – Is There a 13th Sign? – The Precession of the Equinoxes – 2025
This article presents the astrological perspective, explaining that the tropical zodiac is fixed to the seasons, not the constellations, which is why the ‘controversy’ is unfounded.
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