Birth chart guidesMethod and accuracy
Tropical vs sidereal zodiac: did your sign change?
By the Hourwyn team
No, your sign did not change. Western astrology uses the tropical zodiac, which is tied to the seasons: Aries begins at the March equinox every year. The sidereal zodiac, used in Indian (Vedic) astrology, is tied to the stars and currently sits about 24 degrees behind, so most people have the previous sign in that system. Both are conventions, and neither is a correction of the other.
Two zodiacs
| Tropical | Sidereal | |
|---|---|---|
| Anchored to | The seasons | The fixed stars |
| 0° of Aries is | Where the Sun stands at the March equinox | A fixed point among the stars |
| Used in | Western astrology | Indian (Vedic) astrology and some Western astrologers |
| Aries season begins | About March 20 | About April 14 |
Why they drifted apart
Earth's axis wobbles slowly, like a spinning top, and completes a circle in about 26,000 years. Because of this the equinox point slides backward against the stars by one degree roughly every 72 years. The two zodiacs lined up around 1,700 years ago. Since then the gap has grown to about 24 degrees, most of one sign.
Signs are not constellations
A sign is one of twelve equal slices of the Sun's path, 30 degrees each. A constellation is a pattern of stars, and the patterns along that path are very unequal in size. The two share names because the system was named when they roughly lined up.
The thirteenth sign story
Every few years a headline says the zodiac has a new thirteenth sign, Ophiuchus, and that everyone's sign has moved. The astronomy in the story is old news: the Sun does pass through thirteen constellations, Ophiuchus among them, from about November 30 to December 17. The conclusion does not follow. The twelve signs are equal divisions of the circle, and have been since Babylonian astronomers set them up. No astrological system gained a sign.
Which one should you use?
Use the zodiac that matches what you read. Descriptions written by Western astrologers assume tropical positions, and Vedic ones assume sidereal. Mixing them, such as reading a Western description of Taurus for a sidereal Taurus Sun, gives you text written for a different part of the sky.
Common questions
Is Ophiuchus a zodiac sign?
It is a constellation the Sun passes through, not one of the twelve signs. The signs are equal 30° divisions of the Sun's path, and there are twelve in both the tropical and the sidereal zodiac.
How do I find my sidereal sign?
Subtract about 24° from each tropical position. A planet in the first 24 degrees of a sign falls in the previous sign in the sidereal zodiac, and a planet in the last 6 degrees stays where it is.
Is Vedic astrology more accurate than Western astrology?
Neither has been shown to describe people accurately in controlled tests. They are different traditions with different rules. Both calculate the planets' positions exactly.
Why do sun sign dates differ by a day between sources?
The moment the Sun enters each sign shifts by a few hours every year and resets with leap years. A calculated chart uses the exact moment for your birth year.
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Sources
- Axial precession. Wikipedia.
- What's the difference between astrology and astronomy?. NASA Space Place.
The guides are written by Hourwyn with the help of AI tools. Astronomical and historical facts are checked against the sources listed under each guide. Astrology is described as a tradition and offered for entertainment. Nothing here is medical, financial, legal or psychological advice.