Module: AstroChart::SolarArc

Defined in:
lib/astro_chart/solar_arc.rb

Overview

Solar arc directions (太陽弧正向推運): advance every natal point by a single arc — the distance the secondary-progressed Sun has travelled since birth. Unlike secondary progressions (where each body moves at its own rate), solar arc moves the whole chart rigidly, so directed-to-natal aspects perfect at a rate of ~1° per year of life.

natal  = AstroChart::Chart.new(...).generate
result = AstroChart::SolarArc.directions(natal, "2026-07-24")
result["arc"]              # degrees the chart has been directed (~age)
result["planets"]          # directed positions + natal-house placement
result["aspects_to_natal"] # directed→natal aspects, sorted by orb

Constant Summary collapse

DAYS_PER_YEAR =

matches Progressions

365.2425
SUN = 
"太陽"

Class Method Summary collapse

Class Method Details

.directions(natal_chart, target_date, orb_limit: 1.0) ⇒ Object

natal_chart: a Chart#generate result hash (its input block gives birth date/time/timezone). target_date: "YYYY-MM-DD". orb_limit: keep only directed-to-natal aspects within this orb (default 1.0 — solar arc is slow, only near-exact contacts matter).



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# File 'lib/astro_chart/solar_arc.rb', line 27

def self.directions(natal_chart, target_date, orb_limit: 1.0)
  input = natal_chart&.dig("input")
  if input.nil? || input["birth_date"].nil? || input["birth_time"].nil? || input["timezone"].nil?
    raise ArgumentError, "chart has no input data (birth_date/birth_time/timezone required)"
  end

  jd_natal  = TimeConversion.to_julian_day(input["birth_date"], input["birth_time"], input["timezone"])
  jd_target = TimeConversion.to_julian_day(target_date, input["birth_time"], input["timezone"])
  jd_prog   = jd_natal + (jd_target - jd_natal) / DAYS_PER_YEAR # a day for a year

  natal_positions = Synastry.positions_from_chart(natal_chart)
  natal_cusps     = Synastry.cusps_from_chart(natal_chart)

  natal_sun = natal_positions[SUN] || Planets.calculate_positions(jd_natal)[SUN]
  prog_sun  = Planets.calculate_positions(jd_prog)[SUN]
  # The Sun only ever moves forward, so the forward arc is the plain
  # modular difference (< 360° for any human lifespan).
  arc = (prog_sun - natal_sun) % 360.0

  directed_positions = natal_positions.transform_values { |lon| (lon + arc) % 360.0 }

  {
    "arc" => arc.round(4),
    "planets" => Transits.planet_details(directed_positions, natal_cusps),
    "aspects_to_natal" => Transits.aspects_to_natal(
      directed_positions, natal_positions,
      orb_limit: orb_limit,
      keys: %w[directed_planet natal_planet]
    ),
  }
end