Class: Zodiacly::Ephemeris

Inherits:
Object
  • Object
show all
Defined in:
lib/zodiacly/ephemeris.rb

Constant Summary collapse

BODY_TO_COMMAND =

Horizons target IDs (common major bodies)

{
  sun: "10",
  moon: "301",
  mercury: "199",
  venus: "299",
  mars: "499",
  jupiter: "599",
  saturn: "699",
  uranus: "799",
  neptune: "899",
  pluto: "999"
}.freeze
DEFAULT_BODIES = 
%i[sun moon].freeze

Class Method Summary collapse

Class Method Details

.at(time_utc = Time.now.utc, center: "500@399", bodies: DEFAULT_BODIES, cache_ttl: 3600) ⇒ Object

Public API: Zodiacly::Ephemeris.at(time, bodies:)

bodies:

- Array of symbols (e.g. %i[sun moon mars])
- :all (for all supported major bodies)

cache_ttl:

- seconds to keep cached results (default: 3600)


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# File 'lib/zodiacly/ephemeris.rb', line 37

def self.at(time_utc = Time.now.utc, center: "500@399", bodies: DEFAULT_BODIES, cache_ttl: 3600)
  time = Time.parse(time_utc.to_s).utc
  iso  = time.iso8601

  bodies =
    if bodies == :all
      %i[
        sun moon mercury venus mars
        jupiter saturn uranus neptune pluto
      ]
    else
      Array(bodies).map(&:to_sym)
    end

  cache_key = Digest::SHA256.hexdigest([
    iso,
    center,
    bodies.sort.join(",")
  ].join("|"))

  cache_fetch(cache_key, cache_ttl) do
    results = {}

    bodies.each do |body|
      command = BODY_TO_COMMAND.fetch(body) do
        raise Zodiacly::Error, "Unknown body: #{body.inspect}. Known: #{BODY_TO_COMMAND.keys.join(", ")}"
      end

      json = Zodiacly::Horizons.vectors(command: command, center: center, time_utc: iso)
      vec  = parse_vectors(json)

      lon   = ecliptic_longitude_deg(vec[:x], vec[:y])
      speed = ecliptic_longitude_speed_deg_per_day(vec[:x], vec[:y], vec[:vx], vec[:vy])

      results[body] = {
        lon: lon.round(2),
        sign: Zodiacly::Zodiac.sign_for_lon(lon),
        retrograde: speed.negative?,
        speed: speed.round(4)
      }
    end

    {
      time_utc: iso,
      center: center,
      bodies: results
    }
  end
end

.cache_fetch(key, ttl) ⇒ Object 



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# File 'lib/zodiacly/ephemeris.rb', line 145

def self.cache_fetch(key, ttl)
  dir = File.join(Dir.tmpdir, "zodiacly-cache")
  FileUtils.mkdir_p(dir)

  path = File.join(dir, "#{key}.json")

  if File.exist?(path) && (Time.now - File.mtime(path) < ttl)
    return JSON.parse(File.read(path), symbolize_names: true)
  end

  data = yield
  File.write(path, JSON.pretty_generate(data))
  data
end

.ecliptic_longitude_deg(x, y) ⇒ Object

---- Math ----



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# File 'lib/zodiacly/ephemeris.rb', line 126

def self.ecliptic_longitude_deg(x, y)
  rad = Math.atan2(y, x)
  deg = rad * 180.0 / Math::PI
  deg %= 360.0
  deg += 360.0 if deg.negative?
  deg
end

.ecliptic_longitude_speed_deg_per_day(x, y, vx, vy) ⇒ Object

Angular speed of longitude using planar angular velocity: omega = (xvy - yvx) / (x^2 + y^2) [rad/s] convert to deg/day



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# File 'lib/zodiacly/ephemeris.rb', line 137

def self.ecliptic_longitude_speed_deg_per_day(x, y, vx, vy)
  r2 = (x * x) + (y * y)
  return 0.0 if r2.zero?

  omega = (x * vy - y * vx) / r2 # rad / s
  omega * (180.0 / Math::PI) * 86_400.0
end

.extract_soe_line(result_text) ⇒ Object

Raises:



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# File 'lib/zodiacly/ephemeris.rb', line 112

def self.extract_soe_line(result_text)
  start_idx = result_text.index("$$SOE")
  stop_idx  = result_text.index("$$EOE")
  raise Zodiacly::Error, "Horizons result missing $$SOE/$$EOE markers" unless start_idx && stop_idx

  block = result_text[(start_idx + 5)...stop_idx].strip
  # Take the first non-empty line
  line = block.lines.map(&:strip).find { |l| !l.empty? }
  raise Zodiacly::Error, "Horizons SOE block was empty" unless line
  line
end

.parse_vectors(json) ⇒ Object

Horizons JSON has a "result" string which contains a table between $$SOE and $$EOE. With CSV_FORMAT=YES and VEC_TABLE=2, each row is CSV and includes x,y,z,vx,vy,vz.



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# File 'lib/zodiacly/ephemeris.rb', line 91

def self.parse_vectors(json)
  result = json.fetch("result") { raise Zodiacly::Error, "Horizons response missing 'result' key" }

  line = extract_soe_line(result)
  parts = line.split(",").map(&:strip)

  # We expect the last 6 CSV columns to be numeric x,y,z,vx,vy,vz (in km and km/s typically)
  nums = parts.last(6).map { |v| Float(v) }

  {
    x: nums[0],
    y: nums[1],
    z: nums[2],
    vx: nums[3],
    vy: nums[4],
    vz: nums[5]
  }
rescue KeyError, ArgumentError => e
  raise Zodiacly::Error, "Failed to parse Horizons vectors: #{e.message}"
end