Sidereal vs tropical
Sidereal vs tropical: your planets in both zodiacs
The same sky, two zodiacs. See where each of your planets falls in the tropical zodiac most Western charts use and in the sidereal zodiac used in Vedic astrology.
Sidereal vs tropical: the short answer
Sidereal vs tropical is a question about where the zodiac begins. Tropical astrology, the system behind most Western horoscopes, starts Aries at the March equinox and ties the twelve signs to the seasons. Sidereal astrology starts Aries at a fixed point among the stars and ties the signs to the sky. Both split the circle into twelve signs of 30 degrees. They simply start counting from places that are now about 24 degrees apart.
The planets are in the same place whichever you choose. Only the sign names and degrees change, so one planet can be in Gemini in one system and Taurus in the other. The tool above shows every planet in both zodiacs for your own birth, with the changes marked.
Seasons versus stars
The Sun appears to travel once a year around a circle of sky called the ecliptic. Tropical astrology divides that circle starting from the point where the Sun crosses the celestial equator each spring. That moment, the March equinox, is tied to the seasons: the Sun is always at 0 degrees Aries on the first day of spring in the northern hemisphere.
Sidereal astrology divides the same circle starting from a fixed star position. In the Lahiri system, the star Spica sits at 0 degrees of Libra, which pins everything else in place. A sign in this system is therefore a region of the sky you can point to at night.
Each choice has a clear logic. Tropical keeps astrology tied to the Earth's year, with its seasons and light. Sidereal keeps it tied to the constellations and the stars behind the planets.
Why the two zodiacs drifted apart
They were close to identical about 1,700 years ago. Earth's axis wobbles like a spinning top, one full turn taking about 26,000 years. This is called the precession of the equinoxes. As the axis wobbles, the March equinox slides backwards against the stars by around 50 arc-seconds each year, which adds up to roughly 1 degree every 72 years.
The tropical zodiac follows the equinox as it moves. The sidereal zodiac stays on the stars. The angle between them is the ayanamsa. It is about 24.2 degrees in 2026 under the Lahiri system and keeps growing. This is why the old rule of thumb that sidereal signs run about three and a half weeks behind tropical ones is roughly right today, and why the gap will slowly grow.
Side-by-side comparison
| Tropical | Sidereal | |
|---|---|---|
| Reference point | The March equinox, so the signs follow the seasons | A fixed point among the stars, so the signs follow the sky |
| Where Aries starts | Where the Sun is at the equinox, around 20 March | About 24 degrees further along the sky, where the Sun is around 14 April |
| Drift | Moves with the equinox, so it stays tied to the seasons | Stays put against the stars; the gap grows about 1 degree every 72 years |
| Who uses it | Most Western astrologers | Vedic astrology and a minority of Western astrologers |
| Typical Sun sign effect | The sign you know from newspapers | Usually the sign before it, if born in the first 24 days or so |
For a fuller introduction to the sidereal side, including who uses it and what an ayanamsa is, read sidereal astrology explained.
Which one is right?
Honestly, it depends on what you mean by right. They are two reference frames for the same sky, and each is internally consistent. A tropical chart is correct about where a planet sits relative to the equinox. A sidereal chart is correct about where it sits relative to the stars. Neither is a mistake, and neither can be said to be the only valid way to divide the circle.
Neither has been shown to predict events in controlled studies, so the test that matters is personal. Read the description of your Sun, Moon and Rising in each system and notice which one explains your life better. Some people find the tropical signs fit the way they present themselves. Others feel the sidereal signs describe how they actually behave. It is fine to keep both.
What it means for your Sun, Moon and Rising
Sun signs change least often, because the Sun moves about a degree a day. If you were born in the last week or so of a sign, you usually keep it. If you were born earlier, your sidereal Sun is usually the sign before.
The Moon covers about 13 degrees a day, so its sign depends on the exact day and hour, and it changes sign for roughly four people in five. The Rising sign depends on the minute you were born and changes about every two hours, so it is the most sensitive to an accurate time. If you only want these three, the Vedic sign calculator lays them out side by side.
A real chart in both zodiacs
This is one real birth, 15 May 1990 at 10:30 in Delhi, calculated by the same engine as the tool, with an ayanamsa of 23.72 degrees. Bold rows show a sign change.
| Point | Tropical | Sidereal |
|---|---|---|
| Sun | 24°07' Taurus | 0°24' Taurus |
| Moon | 22°42' Capricorn | 28°59' Sagittarius |
| Mercury ℞ | 8°03' Taurus | 14°20' Aries |
| Venus | 12°29' Aries | 18°46' Pisces |
| Mars | 18°07' Pisces | 24°24' Aquarius |
| Rising | 3°37' Leo | 9°53' Cancer |
The Sun is the exception. At 24 degrees of Taurus, subtracting 23.72 leaves it just past the start of the same sign. Everything else steps back one sign. Mercury was retrograde, and that holds in both systems because retrograde motion is about the planets' orbits, not the zodiac.
A second birth, 1 January 2000 at noon in New York, behaves the usual way. Its Sun goes from 10 degrees of Capricorn to 16 degrees of Sagittarius, and Venus goes from 2 degrees of Sagittarius to 8 degrees of Scorpio. In a third, 20 August 1985 in London, the Sun at 28 degrees of Leo stays in Leo at 4 degrees, while Venus moves from Cancer to Gemini.
Do other ayanamsas change the answer?
Sidereal astrologers do not all agree on exactly where the stars should anchor the zodiac. Lahiri is the most common choice and the one used here. Others, such as Raman, Krishnamurti and Fagan-Bradley, differ from it by anything from a few arc-minutes to about a degree and a half. For most planets that makes no difference at all, because the planet sits well inside a sign.
It matters only when a planet is within a degree or two of a sign edge. In that case, two sidereal astrologers can honestly give different signs for the same person. If one of your placements lands that close to an edge, note it as borderline and read both neighbouring signs.
How to use the comparison
Enter your details in the tool and look at the rows in bold. Those are the placements that give you two different descriptions. Begin with the Moon and Rising, then check whether the Sun has moved. Where the signs agree, the two systems tell the same story. Where they differ, you get a second view to test against your experience.
The calculation is explained on the method page, including how we handle the ayanamsa and the Moon. The positions come from a Swiss Ephemeris based engine and are accurate to a fraction of a degree. The Rising sign needs a birth time to within about 15 minutes, so if you do not know yours, treat that row as a guess. When you want the meaning of the planets in your chart, ask Vedica in the chat.
Questions people ask
What is the difference between sidereal and tropical astrology?
Tropical astrology starts the zodiac at the March equinox, so signs follow the seasons. Sidereal astrology starts it at a fixed point among the stars. The planets are in the same place in the sky either way. Only the sign labels move, which is why a planet can be in Gemini in one system and Taurus in the other.
Why are the two zodiacs about 24 degrees apart?
Earth's axis wobbles slowly, a cycle of about 26,000 years called precession. The two zodiacs lined up around the year 285 CE by the Lahiri reckoning, and the equinox has since slid backwards against the stars by roughly 24 degrees. That gap is the ayanamsa and it grows by about 50 arc-seconds a year.
Which one is correct?
Neither is proven to predict anything, and each is internally consistent. Tropical astrology ties meaning to the seasons and the Sun's cycle. Sidereal astrology ties it to the star background. Which one feels right is a personal choice, which is why this tool shows both rather than telling you to drop one.
Will all my planets change sign?
Not all. A planet changes sign when its degree in the tropical sign is below about 24. A planet at 25 degrees or later usually stays in the same sign. Across a whole chart, most people find several planets move back a sign, and the table above marks which ones do for you.
What do the retrograde marks mean?
A retrograde planet appears to move backwards against the stars as seen from Earth. This is an effect of relative orbits, and it is the same in both zodiacs. We flag it because Vedic and Western astrology both read retrograde placements as worth noting, although they interpret them differently.
Why do the nodes show as Rahu and Ketu?
The Moon's north and south nodes are called Rahu and Ketu in Vedic astrology, where they count as full planets in the chart. This tool uses the mean node, the usual choice. In both zodiacs they sit exactly opposite each other and are always shown as retrograde.