Module: AstroChart::Progressions

Defined in:
lib/astro_chart/progressions.rb

Overview

Secondary progressions (二次推運): "a day for a year".

For a target date N years after birth, the progressed chart is the sky N days after birth: jd_prog = jd_natal + years_elapsed, where years_elapsed = (jd_target - jd_natal) / 365.2425.

Typical usage with a Chart#generate result:

AstroChart::Progressions.secondary(natal_chart, "2026-07-24")

Constant Summary collapse

DAYS_PER_YEAR =

Mean Gregorian year length in days (matches the calendar's 400-year cycle).

365.2425

Class Method Summary collapse

Class Method Details

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

Secondary-progressed positions for a natal chart at a target date.

natal_chart: a Chart#generate result hash (its "input" block supplies birth date/time/timezone, so jd_natal is reconstructed exactly). target_date: "YYYY-MM-DD". The target moment is taken at the same local birth time + timezone, so whole calendar years elapse cleanly. orb_limit: keep only progressed-to-natal aspects with orb <= limit (default 1.0 — progressions move slowly, only exact contacts matter).

Returns:

{
"progressed_jd" => 2447926.72,
"years_elapsed" => 30.0,
"planets" => [ { "planet" => "太陽", "zodiac" => "獅子座",
                 "degree" => 9.87, "total_degree" => 129.87,
                 "natal_house" => 3 }, ... 12 entries ],
"aspects_to_natal" => [ { "progressed_planet" => "月亮",
                          "natal_planet" => "金星",
                          "aspect_type" => "三分相", "orb" => 0.4 }, ... ]
}

aspects_to_natal are sorted by orb (tightest first).



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# File 'lib/astro_chart/progressions.rb', line 40

def self.secondary(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"])

  years_elapsed = (jd_target - jd_natal) / DAYS_PER_YEAR
  jd_prog = jd_natal + years_elapsed # a day for a year

  progressed_positions = Planets.calculate_positions(jd_prog)
  natal_positions      = Synastry.positions_from_chart(natal_chart)
  natal_cusps          = Synastry.cusps_from_chart(natal_chart)

  {
    "progressed_jd" => jd_prog,
    "years_elapsed" => years_elapsed.round(2),
    "planets" => Transits.planet_details(progressed_positions, natal_cusps),
    "aspects_to_natal" => Transits.aspects_to_natal(
      progressed_positions, natal_positions,
      orb_limit: orb_limit,
      keys: %w[progressed_planet natal_planet]
    ),
  }
end