Sidereal Modes (Ayanamsas) #

Kerykeion supports both Tropical (default) and Sidereal zodiac systems. When using the Sidereal zodiac, you must specify an ayanamsa (sidereal mode) that defines the starting point of the zodiac relative to the fixed stars.

Tropical vs Sidereal #

Due to the precession of the equinoxes, the tropical and sidereal zodiacs differ by approximately 24° (as of 2024). This difference grows by about 1° every 72 years.

Available Sidereal Modes #

Examples #

Lahiri (Vedic Standard) #

The most widely used ayanamsa for Vedic astrology:

from pathlib import Path
from kerykeion import AstrologicalSubjectFactory
from kerykeion.chart_data_factory import ChartDataFactory
from kerykeion.charts.chart_drawer import ChartDrawer

sidereal_subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon Lahiri", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    zodiac_type="Sidereal",
    sidereal_mode="LAHIRI",
)

print(f"Sun (Lahiri): {sidereal_subject.sun.sign} {sidereal_subject.sun.position:.2f}°")
# Compare: Tropical Sun would be Libra 16.27°

data = ChartDataFactory.create_natal_chart_data(sidereal_subject)
chart = ChartDrawer(data)

out_dir = Path("charts_output")
out_dir.mkdir(exist_ok=True)
chart.save_svg(output_path=out_dir, filename="lennon-lahiri")

Output:

Sun (Lahiri): Vir 23.08°

The chart output:

Fagan-Bradley (Western Sidereal) #

The standard ayanamsa for Western sidereal astrologers:

from kerykeion import AstrologicalSubjectFactory

subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon - Fagan-Bradley", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    zodiac_type="Sidereal",
    sidereal_mode="FAGAN_BRADLEY",
)

print(f"Sun (Fagan-Bradley): {subject.sun.sign} {subject.sun.position:.2f}°")

Krishnamurti (KP System) #

Used for the popular Krishnamurti Paddhati system:

from kerykeion import AstrologicalSubjectFactory

subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon - KP", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    zodiac_type="Sidereal",
    sidereal_mode="KRISHNAMURTI",
)

print(f"Sun (KP): {subject.sun.sign} {subject.sun.position:.2f}°")

Comparing Ayanamsas #

See how different ayanamsas affect planetary positions:

from kerykeion import AstrologicalSubjectFactory

modes = ["LAHIRI", "FAGAN_BRADLEY", "KRISHNAMURTI", "RAMAN"]

for mode in modes:
    subject = AstrologicalSubjectFactory.from_birth_data(
        "Test", 1990, 6, 15, 12, 0,
        lng=-0.1276, lat=51.5074, tz_str="Europe/London",
        online=False,
        zodiac_type="Sidereal",
        sidereal_mode=mode,
    )
    print(f"{mode}: Sun at {subject.sun.sign} {subject.sun.position:.2f}°")

Output:

LAHIRI: Sun at Tau 29.85°
FAGAN_BRADLEY: Sun at Gem 0.62°
KRISHNAMURTI: Sun at Tau 29.78°
RAMAN: Sun at Tau 28.25°

Note: The differences between ayanamsas can be significant (up to a few degrees), which may change the sign a planet falls in, especially for planets near sign boundaries.

Tropical vs Sidereal Comparison #

from kerykeion import AstrologicalSubjectFactory

# Same birth data, different zodiac types
tropical = AstrologicalSubjectFactory.from_birth_data(
    "Tropical", 1990, 6, 15, 12, 0,
    lng=-0.1276, lat=51.5074, tz_str="Europe/London",
    online=False,
    zodiac_type="Tropical",
)

sidereal = AstrologicalSubjectFactory.from_birth_data(
    "Sidereal", 1990, 6, 15, 12, 0,
    lng=-0.1276, lat=51.5074, tz_str="Europe/London",
    online=False,
    zodiac_type="Sidereal",
    sidereal_mode="LAHIRI",
)

print("Tropical positions:")
print(f"  Sun: {tropical.sun.sign} {tropical.sun.position:.2f}°")
print(f"  Moon: {tropical.moon.sign} {tropical.moon.position:.2f}°")
print(f"  Ascendant: {tropical.first_house.sign} {tropical.first_house.position:.2f}°")

print("\nSidereal (Lahiri) positions:")
print(f"  Sun: {sidereal.sun.sign} {sidereal.sun.position:.2f}°")
print(f"  Moon: {sidereal.moon.sign} {sidereal.moon.position:.2f}°")
print(f"  Ascendant: {sidereal.first_house.sign} {sidereal.first_house.position:.2f}°")

Output:

Tropical positions:
  Sun: Gem 24.05°
  Moon: Sco 15.23°
  Ascendant: Vir 24.52°

Sidereal (Lahiri) positions:
  Sun: Tau 29.85°
  Moon: Lib 21.03°
  Ascendant: Leo 0.32°

Important: You cannot set a sidereal_mode when using zodiac_type="Tropical". Attempting to do so will raise a KerykeionException.

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