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Kerykeion

Composite Subject Factory #

The CompositeSubjectFactory creates a new astrological subject representing the relationship between two people using the Midpoint Method. The resulting chart represents the relationship itself as a third entity.

What Is a Composite Chart? #

Unlike Synastry (which compares two separate charts), a Composite Chart creates a single unified chart that symbolizes the relationship itself. Think of it as the “birth chart” of the relationship.

How It Works:

  • Every planetary position is calculated as the midpoint between the two natal charts
  • The Composite Sun shows the relationship’s core identity and purpose
  • The Composite Moon reveals the emotional dynamics between partners
  • House placements show which life areas the relationship emphasizes

Composite charts are especially useful for understanding:

  • Romantic partnerships: What does this relationship want to become?
  • Business partnerships: What are the shared goals and challenges?
  • Friendships: What unique dynamic emerges when these two people interact?

Basic Usage #

The process involves creating two individual subjects first, then generating a composite from them.

from kerykeion import AstrologicalSubjectFactory, CompositeSubjectFactory

# 1. Create Individual Subjects
person_a = AstrologicalSubjectFactory.from_birth_data("Alice", 1990, 6, 15, 14, 30, "London", "GB")
person_b = AstrologicalSubjectFactory.from_birth_data("Bob", 1992, 9, 22, 18, 45, "Los Angeles", "US")

# 2. Create Composite Factory
composite_factory = CompositeSubjectFactory(
    person_a,
    person_b,
    chart_name="Alice & Bob Composite" # Optional custom name
)

# 3. Get the Composite Subject Model
composite_subject = composite_factory.get_midpoint_composite_subject_model()

print(f"Composite Sun: {composite_subject.sun.sign} {composite_subject.sun.abs_pos:.2f}°")

Chart Generation #

The returned composite_subject is a standard AstrologicalSubjectModel. You can use it just like a natal subject to generate chart data or SVG visualizations.

from kerykeion import ChartDataFactory
from kerykeion.charts.chart_drawer import ChartDrawer

# Generate Data
composite_data = ChartDataFactory.create_composite_chart_data(composite_subject)

# Draw Chart
drawer = ChartDrawer(composite_data)
svg = drawer.generate_svg_string()

Requirements #

To calculate a valid composite chart, both subjects MUST have matching configuration:

  • Zodiac System: Both Tropical OR Both Sidereal (with same Ayanamsa).
  • House System: Both Placidus, Whole Sign, etc.
  • Perspective: Both Apparent Geocentric, etc.

If these settings do not match, the factory will raise an error, as you cannot mathematically combine disparate coordinate systems.

Methodology #

  • Midpoints: Positions are calculated as the shortest arc mean between the two input points (e.g., Aries 0° and Aries 20° = Aries 10°).
  • House Cusps: House cusps are also calculated by midpoint.
  • Active Points: Only points present in both input subjects are included in the composite.