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.

Kerykeion supports 48 sidereal modes (47 named + USER for custom definitions).

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 #

Classic Modes #

Extended Modes #

Custom Ayanamsa (USER Mode) #

The USER sidereal mode lets you define a custom ayanamsa by providing a reference epoch and offset:

from kerykeion import AstrologicalSubjectFactory

custom = AstrologicalSubjectFactory.from_birth_data(
    "Custom Ayanamsa", 2000, 1, 1, 0, 0,
    lng=0.0, lat=51.5, tz_str="Etc/GMT", online=False,
    zodiac_type="Sidereal",
    sidereal_mode="USER",
    custom_ayanamsa_t0=2451545.0,      # J2000.0 reference epoch (Julian Day)
    custom_ayanamsa_ayan_t0=23.5,       # Ayanamsa offset at epoch (degrees)
)

print(f"Sun (Custom): {custom.sun.sign} {custom.sun.position:.2f}")
print(f"Ayanamsa value: {custom.ayanamsa_value:.4f}")

Both custom_ayanamsa_t0 and custom_ayanamsa_ayan_t0 are required when using sidereal_mode="USER". Omitting either will raise a KerykeionException.

Accessing the Ayanamsa Value #

For any sidereal chart, the computed ayanamsa offset (in degrees) is available via ayanamsa_value:

from kerykeion import AstrologicalSubjectFactory

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

print(f"Ayanamsa value: {subject.ayanamsa_value:.4f}°")
# e.g. 23.7273° -- the tropical-sidereal offset for this date

ayanamsa_value is None for tropical charts.

A rendered chart names the ayanamsa mode but not its offset. Pass show_ayanamsa_value=True to ChartDrawer to append the value to that line — Ayanamsa: Lahiri (23°43'). The mode names the convention; the offset says where it actually put the zodiac for this date, which is what differs between two charts drawn under the same ayanamsa centuries apart. Degrees and minutes only, and nothing at all on a tropical chart.

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.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", style="classic")

Output:

Sun (Lahiri): Vir 23.24°

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 Gem 0.36°
FAGAN_BRADLEY: Sun at Tau 29.48°
KRISHNAMURTI: Sun at Gem 0.46°
RAMAN: Sun at Gem 1.81°

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 24.09°
  Moon: Pis 14.80°
  Ascendant: Vir 14.74°

Sidereal (Lahiri) positions:
  Sun: Gem 0.36°
  Moon: Aqu 21.07°
  Ascendant: Leo 21.02°

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

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