Methodology

Zodiac and ayanamsa

Positions are sidereal, measured from a fixed point among the stars. The default ayanamsa is Lahiri, also called Chitrapaksha. It is named after N. C. Lahiri, Secretary of the Calendar Reform Committee, which India’s Council of Scientific and Industrial Research appointed in 1952 under M. N. Saha. Like the nakshatra tables in the Committee’s 1955 report, it places the star Spica (Chitra) at 180°. The report itself sets the start of the religious solar year at 23° 15′ of tropical longitude.

The calculation settings also offer B. V. Raman, Krishnamurti (KP), True Chitra, True Revati, Sri Yukteshwar, Surya Siddhanta and Fagan-Bradley, and the tropical zodiac. Each chart states the ayanamsa it used and its value in degrees at the birth moment.

Source: Report of the Calendar Reform Committee (CSIR, 1955), pp. 184 and 251.

Ephemeris, time and place

Planetary positions are computed with the Swiss Ephemeris, using its data files based on JPL’s DE441 ephemeris. The calculation engine is open source under the AGPL: github.com/astroscorpio/engine. A local birth time is converted to Universal Time with the IANA time zone database, which carries each place’s historical clock changes. When a clock change made a local time happen twice, the calculation asks for the UTC offset from the birth record.

Places come from GeoNames (populated places with 500 or more people), used under the CC BY 4.0 licence.

Lunar nodes

Rahu and Ketu are the true lunar nodes by default. The mean node is in the calculation settings, and the choice applies to charts and transits alike.

Houses and divisional charts

Houses are whole signs counted from the lagna: the rising sign is the first house, the next sign the second, and so on round the zodiac.

Without a birth time the chart is a Moon chart (Chandra lagna), with houses counted from the Moon’s sign. The lagna and the divisional charts depend on the exact time, so they are left out and marked.

The divisional charts are the sixteen of the shodashavarga, from D1 to D60.

Sunrise and the day

Sunrise and sunset are the moments when the centre of the Sun’s disc crosses the horizon, allowing for atmospheric refraction. The Vedic day runs from one sunrise to the next, so the weekday (vara) changes at sunrise.

Tithi, nakshatra, yoga and karana

• A tithi is each 12° the Moon gains on the Sun, 30 to a lunar month.
• A nakshatra is each 13° 20′ of the Moon’s sidereal longitude, 27 round the zodiac.
• A yoga is each 13° 20′ of the Sun’s and Moon’s longitudes added together.
• A karana is half a tithi, 6°. Seven movable karanas, Bava to Vishti, repeat eight times a month. Four fixed karanas, Kimstughna, Shakuni, Chatushpada and Naga, fall at the turn of the month.

The panchang shows the limbs current at sunrise, then each one that begins before the next sunrise, with its start and end times.

Source: Sūrya-siddhānta 2.64⁠–⁠69, tr. Ebenezer Burgess, pp. 104⁠–⁠107.

Rahu kalam, Yamaganda and Gulika kalam

Each is one eighth of the daytime, from sunrise to sunset. Which eighth depends on the weekday:

Kalaprakasika gives these periods as clock times for a day running from 6:00 to 18:00. The panchang applies the same division into eighths to the real length of each day at the chosen place, so the times move with sunrise and sunset through the year.

North India also uses another system under similar names, based on fifteenths of the day (Muhurta Chintamani 1.37). This site follows the eighths.

Source: Kālaprakāśikā, tr. N. P. Subramania Iyer (1917), pp. 175⁠–⁠176.

Abhijit muhurta and durmuhurta

The daytime is divided into fifteen muhurtas. Abhijit is the eighth, around local noon. On Wednesdays Abhijit is one of the day’s forbidden muhurtas, so the panchang marks it as avoided.

The forbidden daytime muhurtas (durmuhurta) for each weekday are:

Source: Muhūrta-cintāmaṇi 6.50 and 6.52, with the Pīyūṣadhārā commentary (1945 printing), pp. 274⁠–⁠275.

Brahma muhurta

Brahma muhurta is shown as the fourteenth of the fifteen muhurtas of the night, the one that ends one muhurta before sunrise. On a 12-hour night it runs from 96 to 48 minutes before sunrise. This window is current practice.

The texts place the brāhma muhūrta at the end of the night without fixing this window. Commenting on Manusmṛti 4.92, Kullūka Bhaṭṭa reads it as the last yāma (watch) of the night and Govindarāja as the last muhūrta.

Source: Manusmṛti 4.92, with Kullūka Bhaṭṭa’s commentary (1909), p. 149.

Choghadiya

The daytime and the night are each divided into eight equal parts. Each part is named after the planet that rules it: Udveg (Sun), Char (Venus), Labh (Mercury), Amrit (Moon), Kaal (Saturn), Shubh (Jupiter) and Rog (Mars). The first part of the day belongs to the lord of the weekday.

Amrit, Shubh and Labh are shown as good, Char as neutral, and Udveg, Kaal and Rog as times to avoid.

The classical texts read do not describe choghadiya; the panchang follows current almanac practice.

Hora

The daytime and the night are each divided into twelve equal parts, so a hora is longer than an hour on long days and shorter on short ones. The lords follow the order Sun, Venus, Mercury, Moon, Saturn, Jupiter, Mars: each lord is the sixth, in weekday order, from the one before. The first hora of the day belongs to the lord of the weekday.

Muhurta Chintamani (1.55) gives the same order of lords but uses equal horas of 60 minutes (two and a half ghatis), counted from the start of the weekday.

Source for the order of lords: Kālaprakāśikā, p. 176; Muhūrta-cintāmaṇi 1.55, p. 49.

Vimshottari dasha

The Vimshottari cycle lasts 120 years and is divided among nine planets. The first period of life belongs to the lord of the nakshatra the Moon occupies at birth, and only the part of that nakshatra the Moon has yet to cross remains of the first period. The periods then follow in this order:

A dasha year here is 365.2425 days, the mean Gregorian year. Software differs on this point: 365.25 days (Julian), 365.2422 (tropical), 365.2564 (sidereal) and 360 (savana) are all in use, and none of the texts we have read fixes the count. The first four agree to within two days over the whole cycle. The 360-day year moves late periods by more than a year.

Source: Bṛhaj-jyotiḥsāra vv. 411⁠–⁠414 (1892), p. 150.

Fasts and festivals

Fast and festival days follow the Nirṇaya-sindhu of Kamalākara Bhaṭṭa, with the Dharmasindhu of Kāśīnātha Upādhyāya where it sets the rule. Each page names the test it applies. An Ekadashi is checked for Daśamī at sunrise (the Smārta test) and in the 96 minutes before sunrise (the Vaiṣṇava test). Lakshmi Puja on Diwali falls in pradoṣa on the Amāvasyā. Where the texts give two days, both are shown and labelled. All times use the sunrise and sunset convention above, at the chosen place.

Source: Nirṇaya-sindhu, pariccheda 1, pp. 49⁠–⁠63 and pp. 299⁠–⁠300; Dharmasindhu (1888).

Sources

Each edition is listed with the verses and pages cited on the Sources page.

Send corrections to contact@astroscorpio.com.

Last updated 15 October 2026