Birth Chart

This calculates where the Sun, Moon and planets actually were at a given moment, from a given place on Earth. Then it reads that one sky twice.

Western astrology uses the tropical zodiac, which is anchored to the seasons. Zero degrees of Aries is defined as the March equinox — the point where the Sun crosses the celestial equator going north — and the twelve signs are measured from there.

Vedic astrology uses the sidereal zodiac, which is anchored to the stars.

Those two anchors used to coincide. They no longer do, because the Earth's axis wobbles: the equinox point drifts backwards through the constellations by about one degree every seventy-two years. That is precession, and over roughly eighteen centuries it has opened a gap of about twenty-four degrees between the two zodiacs.

Twenty-four degrees is most of a sign. So a person the Western tradition calls a Taurus is very often a Vedic Aries, and the same is true right down the chart.

The gap has a name — the ayanamsa — and it is shown as a single number above the results. It is the entire difference between the two columns. Every row where the two traditions land in different signs is marked.

Neither column is a correction of the other. They are two different conventions, each internally consistent, each with a long argument behind it. Western astrologers hold that the zodiac is a seasonal framework and that the constellations were only ever a convenient label. Vedic astrologers hold that the stars are the actual referent and that the Western zodiac has simply drifted off its own foundation. Both positions are set out in the Library.

What else is shown

The Moon's nakshatra. Vedic astrology divides the sidereal ecliptic into twenty-seven lunar mansions rather than twelve signs, and the Moon's nakshatra is usually the first thing a Vedic astrologer looks at. Western astrology has no equivalent and does not divide the zodiac this way at all.

Which bodies each tradition actually uses. Hellenistic astrology worked with seven visible bodies and nothing else. Vedic works with nine — the same seven, plus Rahu and Ketu, the two points where the Moon's path crosses the Sun's, treated as full planets in their own right. Modern Western added Uranus, Neptune and Pluto after they were discovered, and treats the nodes as points rather than planets. Three traditions, three different lists, same sky.

Two house systems. Whole sign is the oldest, and is what Hellenistic and Vedic astrology use. Equal house is also ancient. Both are offered and they give different answers.

Placidus, which is the default almost everywhere else, is deliberately not offered. It divides time rather than space, produces houses of very unequal size, and above about sixty-six degrees of latitude it cannot be constructed at all. A tool that prints Placidus cusps for Reykjavik is printing something it cannot justify.

What this does not do

It does not interpret. It gives positions, the sign each falls in under each convention, the house each falls in under the system you pick, and the nakshatra of the Moon. It does not tell you what any of that means about you, and it makes no prediction of any kind.

The arithmetic is checked against published equinox, solstice and new-moon instants and against the Jupiter–Saturn conjunction of December 2020 before every release, and the working is shown under the results.

One warning that matters more than the rest. Historical daylight saving is not applied, and you should set the UTC offset yourself. An hour of error moves the Ascendant about fifteen degrees — half a sign — while leaving the planets essentially untouched. If you were born during summer time and do not adjust for it, the Ascendant and the houses are the parts that will be wrong, and they are the parts that depend on the birth time in the first place.