Tropical vs Sidereal Astrology
Tropical vs sidereal astrology explained: why your sign can differ between the two zodiacs, how each is calculated and which one our calculator uses.
Tropical vs sidereal is the choice between the two main ways to measure the zodiac. Western astrology mostly uses the tropical zodiac, while Vedic (Indian) astrology uses the sidereal zodiac. They can give you different signs, which is why some people find their sign “changes” depending on the website.
The tropical zodiac
The tropical zodiac is tied to the seasons. 0° Aries always begins at the spring equinox in the northern hemisphere, when day and night are equal. It is the system used by most Western astrologers, and it is the system our calculator uses.
The sidereal zodiac
The sidereal zodiac is tied to the background constellations. Because Earth wobbles slowly on its axis, the equinox drifts against the stars over centuries. Today the two zodiacs are about 24° apart, so sidereal placements are usually one sign earlier than tropical ones.
Tropical vs sidereal: which one is right?
Both are internally consistent systems with long traditions. Tropical astrology focuses on the relationship between Earth and the Sun’s seasonal cycle. Sidereal astrology focuses on the stars themselves. Choose the tradition that resonates with you and use it consistently.
- Tropical
- Seasons-based. Used in most Western astrology, horoscopes and our calculator.
- Sidereal
- Star-based. Used in Vedic astrology, about 24° behind tropical today.
Further reading: an overview of sidereal and tropical astrology and its history.
Tropical vs sidereal: your questions answered
Why is my sign different on another website?
That site may use the sidereal zodiac. Sidereal positions are currently about 24° behind tropical, often shifting placements back one sign.
Which zodiac does this calculator use?
The tropical zodiac with whole-sign houses, the most common approach in Western astrology.
Is there a thirteenth sign?
Ophiuchus is a constellation the Sun passes through, but neither the tropical nor traditional sidereal zodiac includes it as a sign.
What Is a Birth Chart?
The Big Three: Sun, Moon and Rising Explained
The 12 Houses in Astrology Enter your birth date, time and city. It is free, private and takes less than a minute.