Astrology is often criticized for being “off” by about a month because the zodiac signs were originally set over 2,000 years ago. But the full picture is more nuanced, especially since different astrologers use different systems to calculate signs—some based on the stars themselves, others on the seasons.
Tropical vs. Sidereal Astrology: Two Different Systems
Most Western astrologers use the tropical zodiac, which fixes the start of Aries at the March equinox—the first day of spring in the Northern Hemisphere. This system divides the ecliptic into twelve equal 30-degree signs based on the Earth’s seasons, not the actual positions of the constellations in the sky. Because of Earth’s slow wobble called axial precession, the background stars have shifted about 24 degrees (nearly a full sign) since the system was created. So, under tropical astrology, the Sun’s position relative to the stars no longer matches the traditional zodiac signs.
On the other hand, sidereal astrology, which is common in Indian (Vedic) astrology and some Western practices, bases signs on the actual positions of the constellations. Sidereal astrologers use a correction called the ayanamsa to adjust for precession and keep the zodiac aligned with the stars. This means that a person’s sidereal Sun sign is often about one sign earlier than their tropical sign. For example, someone who is an Aries in tropical astrology might be a Pisces in sidereal astrology.
Do Some Astrologers Use Actual Planet Positions?
Yes. Both tropical and sidereal astrologers calculate the real-time positions of the planets, Moon, and Sun in the sky. The difference lies in the reference frame they use for the zodiac signs:
– Tropical astrology measures planetary positions relative to the fixed seasonal points (like the equinox).
– Sidereal astrology measures planetary positions relative to the fixed stars and constellations.
Interestingly, while the signs differ, the planetary aspects (angles between planets) and lunar phases happen at the same time in both systems, because the planets move through the same sky.
What About the 13th Constellation, Ophiuchus?
Astronomers recognize 13 constellations along the ecliptic, including Ophiuchus, which lies between Scorpio and Sagittarius. Traditional astrology ignores Ophiuchus and divides the sky into 12 equal signs, so the zodiac signs don’t perfectly match the real constellation boundaries. Some sidereal astrologers consider Ophiuchus, but it’s rare.
Is Astrology Absurd Because of These Differences?
From a scientific perspective, astrology lacks empirical support and its predictive claims don’t hold up under testing. The mismatch between tropical signs and actual star positions highlights that astrology is not astronomy—it’s a symbolic system rooted in tradition, culture, and psychology rather than physical reality.
However, many astrologers and followers find value in astrology as a tool for self-reflection, storytelling, and cultural identity. Both tropical and sidereal systems offer meaningful frameworks, even though they differ in approach.
In Summary
– The zodiac signs set 2,000 years ago no longer align with the stars due to Earth’s precession.
– Tropical astrology is based on seasons and fixed calendar points; sidereal astrology is based on actual star positions.
– Both systems calculate real planetary positions but interpret them differently.
– Astrology is symbolic and cultural, not scientifically proven.
– Whether astrology “works” depends on personal belief and how one uses it.
If you want to explore astrology, it helps to understand these differences and choose the system that resonates with you. But it’s important to remember that astrology is not a science, and the “month off” issue reflects the difference between symbolic tradition and astronomical reality.
Read More
[1] https://en.wikipedia.org/wiki/Sidereal_and_tropical_astrology
[2] https://davidpetrusich.com/sidereal-astrology
[3] https://www.discoverastroyoga.com/blog/tropical-and-sidereal-astrology-two-views-of-the-same-sky
[4] https://www.whitelotusoflight.com/blog/sidereal-vs-tropical-zodiac-and-why-it-matters
[5] https://www.reddit.com/r/Advancedastrology/comments/109j7mr/for_those_of_you_who_have_switch_between_tropical/
[6] https://www.lightonvedicastrology.com/blog/the-sidereal-vs-tropical-debate
[7] https://horoscopes.astro-seek.com/tropical-vs-sidereal-zodiac-astrology-calculator
[8] https://www.ancientastrology.com/articles-/tropical-vs-siderereal-astrology