Astro

About

How Astro works

Astro is a free birth chart and kundli calculator. Every chart is calculated by the page itself, in your browser, from published astronomical theories. There's no server doing the work and no account.

Your privacy

Your name and birth details are never sent anywhere, and never appear in the page's address. The last chart you cast and any charts you save are kept in this browser only, so they're there when you come back. The site counts visits anonymously, without the birth details. See the privacy policy.

The astronomy

  • Planets: the VSOP87 planetary theory of the Bureau des Longitudes (Bretagnon and Francou), with light-time, aberration and nutation, as observatories compute apparent positions.
  • Moon: the main terms of the ELP-2000/82 lunar theory (Chapront-Touzé and Chapront), as given in Jean Meeus's Astronomical Algorithms. Pluto follows the same book.
  • Rahu and Ketu: the mean node, or the true (osculating) node worked out from the Moon's orbit at the moment of birth.
  • Time: your place's time zone, with its daylight saving and historical changes, comes from your browser's own time zone database. Before standard time zones, places kept local mean time, and that's used too. You can always type the UTC offset yourself.
  • Houses: Placidus, Koch, Porphyry, Equal, Whole Sign. Inside the polar circles, where Placidus and Koch don't work, Porphyry is used instead.

Accuracy

Tested against NASA JPL's Horizons ephemeris at 25 dates from 1900 to 2100, the Sun and planets are within 3.5 arcseconds and the Moon within 6. That's far finer than astrology needs: the ascendant moves about 15 arcseconds every second of time. Your birth time is almost always the real limit on accuracy.

Vedic charts use each ayanamsa's published definition, carried forward by precession, so they agree with the usual Indian astrology software. Dashas use years of 365.25 days.

Ayanamsas

Choose one in Settings, under the birth form. Lahiri is the default.

  • Lahiri (Chitrapaksha): India's official ayanamsa: 23°15'00.658" on 21 March 1956, Spica near 0° Libra.
  • B.V. Raman: B.V. Raman's ayanamsa, used in his books and tables.
  • Krishnamurti (KP): K.S. Krishnamurti's ayanamsa for the KP system.
  • Fagan/Bradley: The Western sidereal ayanamsa of Cyril Fagan and Donald Bradley.
  • Sri Yukteshwar: From Sri Yukteshwar's The Holy Science.
  • J.N. Bhasin: J.N. Bhasin's ayanamsa.
  • Ushashashi: Puts Revati (zeta Piscium) near 29°50' Pisces.
  • De Luce: Robert De Luce's ayanamsa.
  • Surya Siddhanta: Zero in 499 CE, from the Surya Siddhanta.
  • Aryabhata: Zero in 499 CE, from Aryabhata's Aryabhatiya.
  • True Chitra: Spica (Chitra) always at exactly 0° Libra.
  • True Pushya: Delta Cancri (Pushya) always at 16° Cancer.
  • True Revati: Zeta Piscium (Revati) always at 29°50' Pisces.
  • Custom value: Your own ayanamsa at J2000 (1 January 2000), carried forward by precession.
  • None (tropical): No ayanamsa: the Vedic charts use the tropical zodiac.

Credits

Places come from GeoNames (CC BY 4.0) and the astrological glyphs from Noto Sans Symbols (SIL Open Font License). Every source and license is listed in credits.txt.