Perspective Type #

The perspective_type parameter defines the viewpoint from which planetary positions are calculated. Kerykeion supports four different perspectives.

Available Perspective Types #

Apparent Geocentric (Default) #

This is the standard perspective for almost all astrological work. It accounts for the time light takes to travel from celestial bodies to Earth.

from kerykeion import AstrologicalSubjectFactory

# Default perspective - no need to specify
subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    # perspective_type="Apparent Geocentric"  # This is the default
)

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

Output:

Sun: Lib 16.27°
Moon: Aqu 3.50°

Heliocentric #

In heliocentric charts, we view the solar system from the Sun’s perspective. The Earth appears in the chart instead of the Sun.

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

subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon - Heliocentric", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    perspective_type="Heliocentric",
)

# Note: In heliocentric, Earth replaces Sun
print(f"Earth: {subject.earth.sign} {subject.earth.position:.2f}°")
print(f"Mars: {subject.mars.sign} {subject.mars.position:.2f}°")

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

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

The output will be:

Note: Heliocentric charts have no houses or Ascendant since there is no observer on Earth. The house system is ignored.

True Geocentric #

Shows positions without light-time correction. The difference from Apparent Geocentric is typically very small (a few arcseconds for most planets).

from kerykeion import AstrologicalSubjectFactory

# True geocentric perspective
subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon - True Geocentric", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    perspective_type="True Geocentric",
)

print(f"Sun: {subject.sun.sign} {subject.sun.position:.4f}°")

Topocentric #

The most precise perspective for the Moon and fast-moving points. Accounts for the observer’s exact location on Earth’s surface (parallax correction).

from kerykeion import AstrologicalSubjectFactory

# Topocentric for precise Moon position
subject = AstrologicalSubjectFactory.from_birth_data(
    "John Lennon - Topocentric", 1940, 10, 9, 18, 30,
    lng=-2.9833, lat=53.4, tz_str="Europe/London",
    online=False,
    perspective_type="Topocentric",
)

print(f"Moon: {subject.moon.sign} {subject.moon.position:.4f}°")
print(f"Ascendant: {subject.first_house.sign} {subject.first_house.position:.4f}°")

Comparing Perspectives #

from kerykeion import AstrologicalSubjectFactory

perspectives = ["Apparent Geocentric", "True Geocentric", "Topocentric"]

for perspective in perspectives:
    subject = AstrologicalSubjectFactory.from_birth_data(
        "Test", 1990, 6, 15, 12, 0,
        lng=-0.1276, lat=51.5074, tz_str="Europe/London",
        online=False,
        perspective_type=perspective,
    )
    print(f"{perspective}:")
    print(f"  Moon: {subject.moon.position:.4f}°")

Output:

Apparent Geocentric:
  Moon: 15.2347°
True Geocentric:
  Moon: 15.2348°
Topocentric:
  Moon: 15.1892°  # Note the larger difference due to parallax

Tip: For most astrological work, stick with the default Apparent Geocentric. Use Topocentric only when precise Moon timing is critical (e.g., for electional astrology or void-of-course Moon calculations).

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