Ayanamsa and Chart Calculation

Inputs that define the chart

A natal chart requires the birth date, recorded local time and place. The reliability of the time matters alongside the number of decimal places shown by software. A record stated approximately should not be presented as accurate to seconds simply because the chart displays arcseconds.

Local civil time is converted using the historical time-zone offset and daylight-saving rules applicable to the location and date. Coordinates, ambiguous place names and a conversion crossing midnight can affect the input record.

Ayanamsa

Ayanamsa is the offset relating tropical and sidereal zodiac longitudes. It reflects the adopted reference for the sidereal zodiac. Sidereal longitude is commonly obtained by subtracting the selected ayanamsa from tropical longitude and normalising within 0–360 degrees.

KP calculations use a specified KP ayanamsa option. Labels such as Original, New and Straight Line should not be treated as interchangeable without checking the program's definitions. Small differences can matter near a star or sub boundary.

Placidus cusps

The usual KP setup uses Placidus house cusps. Houses can have unequal zodiacal spans, and two cusps can fall in one sign while another sign contains none. Whole-sign and other bhava displays do not supply identical occupation results.

At high latitudes a Placidus calculation may encounter limitations. A clearly identified alternative is preferable to silently substituting another system under the same label.

A reproducible record

The complete calculation record includes the ephemeris, software version, exact ayanamsa, house system, node convention and dasha year convention. Comparing those settings is the first step when two programs disagree about a cusp or sub-lord.