Tropical vs sidereal: your chart in five systems
Same sky, same birth, five ways of measuring it. This free tool computes your chart through every major system and lays them out side by side, with each difference highlighted.
Free, no account. Your birth details stay in your browser and are never stored.
Why your sun sign changes between systems
If you have ever typed your birthday into a Vedic astrology site and watched your sun sign slide back one, nothing went wrong. You ran into the oldest open question in astrology: where does the zodiac start?
The tropical zodiac, which most Western astrology uses, starts at the March equinox. Zero degrees Aries is the point where the Sun crosses the celestial equator heading north, every year, forever. The sidereal zodiac, which Jyotish and other star-anchored traditions use, starts from the fixed stars. Around 1,700 years ago the two starting points lined up. Since then Earth's slow wobble, called precession, has drifted them apart by about one degree every 72 years. Today the gap is roughly 24 degrees, which is most of a sign. Anyone born in the last two thirds of a sign shifts back one sign in sidereal reckoning. That single fact explains almost every "wait, I'm a different sign?" moment on the internet.
The measured value of that gap at any moment is called the ayanamsa. The tool uses Lahiri, the value most of Indian astrology standardized on, and shows you the exact ayanamsa at your own birth.
What the tool shows
You enter your birth details once. The tool computes your real chart through five systems and puts them in one table, planet by planet:
- Tropical with Placidus houses, the baseline most Western charts show
- Tropical with Whole Sign houses, which isolates what the house system alone changes
- Sidereal (Lahiri) with Whole Sign houses, the pairing you actually meet in practice
- Draconic, the zodiac rotated so your North Node sits at 0 degrees Aries
- Heliocentric, the view from the Sun, where nothing rises and nothing retrogrades
Cells that land in a different sign than the baseline are highlighted in gold, and house shifts get their own marker, so the real differences jump out instead of hiding in a wall of degrees.
The house problem, briefly
Houses divide the sky by your horizon at the moment of birth, and there has never been one agreed way to cut them. Whole Sign, the oldest method, gives each sign one full house starting from your rising sign. Placidus, the common modern default, divides by rotation time, so its houses stretch and shrink with latitude. Both are legitimate conventions. A planet near a boundary can genuinely sit in different houses under each one, and the table shows you exactly where that happens in your own chart.
So which one is right?
They are different lenses on the same sky, built for different questions. The tropical zodiac measures where a planet stands in the seasonal cycle. The sidereal zodiac measures where it stands against the stars. Draconic measures everything from your lunar nodes, and heliocentric drops the earthbound view altogether. Each one is internally consistent, and none of them contradicts the astronomy: the planets are exactly where they are, and each system is a choice about what to measure them against. Pick the lens that matches the question you are asking.
YouCast's own readings use the tropical zodiac with Placidus houses, and the comparison exists so you can see precisely what that choice means. If you want to walk through these systems in three dimensions, AstroView renders your actual birth sky and lets you switch the zodiac live.
Common questions
Why is my sun sign different in Vedic astrology?
Western astrology usually uses the tropical zodiac, which is anchored to the seasons. Vedic astrology (Jyotish) uses a sidereal zodiac, anchored to the stars. Earth's slow wobble has drifted the two apart by about 24 degrees, so anyone born in roughly the last two thirds of a sign shifts back one sign in sidereal reckoning. The tool shows your sidereal zodiac positions with the Lahiri ayanamsa, the offset Jyotish most commonly starts from, without the interpretive system on top.
Which zodiac is correct, tropical or sidereal?
Both are internally consistent measurements of the same sky from different reference points. The tropical zodiac tracks the seasonal cycle and always starts at the March equinox. The sidereal zodiac tracks the fixed stars. Each answers its own kind of question, and neither one is a mistake.
What is an ayanamsa?
The ayanamsa is the measured angle between the tropical and sidereal zodiacs at a given moment, currently about 24 degrees and growing by about one degree every 72 years. Lahiri is the most widely used value in Indian astrology; other ayanamsas differ from it by fractions of a degree.
What are Whole Sign houses?
Whole Sign is the oldest house system: your rising sign is your first house, the next sign is your second, and each house is one full sign. Placidus, the common modern default, divides houses by time of rotation instead, so its houses vary in size and planets can land in different houses under each method.
What is a draconic chart?
A draconic chart rotates the zodiac so your Moon's North Node sits at 0 degrees Aries. The geometry of your chart stays exactly the same; only the sign labels move. Astrologers who use it read it as a symbolic layer underneath the natal chart.
Is my birth data stored?
No. Every chart is computed in your own browser and your birth details are never stored on any server.