How the Vedic chart engine works

Vedic Astrolab calculates planetary positions from NASA JPL's DE421 ephemeris using the open-source Skyfield library. It converts them to the sidereal zodiac with the Lahiri ayanamsa, assigns whole-sign houses, finds the nakshatra of each planet, and builds the Vimshottari dasha timeline. The same birth details always give the same chart.

• Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn: apparent positions from the DE421 ephemeris, with retrograde motion marked for the planets that can be retrograde.
• Rahu and Ketu: from the mean lunar node (not the true node), always shown as retrograde.
• Each position: sign, degree within the sign, nakshatra (one of 27) and pada (quarter).

Vedic astrology (Jyotish) uses the sidereal zodiac, which is fixed to the stars. The tropical zodiac used in Western astrology is fixed to the seasons, so a person's Vedic Sun or Moon sign is often different from the Western one. Differences like this are normal, not an error.

Vedic Astrolab uses the Lahiri ayanamsa (about 23.85 degrees at the year 2000, growing with precession) to convert tropical positions to sidereal ones, and whole-sign houses: the sign that rises is the first house, the next sign is the second house, and so on.

The rising sign (lagna) needs the birth time and the birthplace. It is calculated from local sidereal time and the latitude of the birthplace. Houses depend on it.

If you do not know your birth time, the engine does not give a rising sign or houses. It uses noon for the Moon but also checks the first and last minute of your birth day, because the Moon moves about 13 degrees a day. If the Moon's sign or nakshatra changes during that day, Vedic Astrolab says it is uncertain instead of guessing.

The Vimshottari dasha is a 120-year cycle of nine planetary periods. It starts from the nakshatra of your Moon and how far the Moon had moved through it at birth. Each main period (mahadasha) is divided into sub-periods (antardasha). Years are counted as 365.25 days.

With an unknown birth time, the running period is stated only when it is the same for the whole birth day.

To talk about the present, the engine also calculates where Jupiter, Saturn, Rahu and Ketu are now, and which house they fall in counted from your Moon sign (and from your rising sign when it is known).

The AI never calculates astrology. It receives a structured summary of your calculated chart and what you wrote in the conversation, and it explains and reflects. It is told to use only that information.

It does not receive your date of birth, email or exact birthplace. See the Privacy Policy for what is shared and why.

It is an AI, not a human astrologer. It can be wrong. Astrology here is a lens for reflection, not a prediction, and it does not give medical, legal or financial advice.

• Rahu and Ketu use the mean node, which can differ slightly from the true node some other tools use.
• The Lahiri ayanamsa is computed from a standard formula; other software may differ by a small fraction of a degree.
• The ephemeris covers roughly the years 1900 to 2050.
• Divisional charts such as the navamsa are not calculated yet.
• Birth times are converted with the time zone of the birthplace; very old or unusual local time rules can cause errors.

Found something that looks wrong? Write to the address below and include the birth details you used. We will check it.