class MoonCalc

Lunar/Moon phases ruby class

Code is based upon Bradley E. Schaefer”s moon phase algorithm. Ruby version based on JavaScript Phase Calculator by Stephen R. Schmitt

Attributes

days[R]

dist[R]

epoch[R]

icon[R]

ll[R]

phase[R]

Public Class Methods

new(epoch=Time.now) click to toggle source

Return the current (or input a date) moon.

Moon.new
Moon.new(some_day)

Methods available:

phase    => Phase of the moon as a sym
days     => Moon days
icon     => An integer from 0 to 29
dist     => Distance in earth radii
ll       => Moon ecliptic lat/lon

# File lib/moon_calc.rb, line 19
def initialize(epoch=Time.now)
  @epoch = epoch
  do_calc
end

Private Instance Methods

calc_coords(inter, phase) click to toggle source

# File lib/moon_calc.rb, line 40
def calc_coords(inter, phase)
  phase = phase * 2 * Math::PI
  dp = 2 * Math::PI * normalize((inter -  2451562.2 ) / 27.55454988)
  @dist = 60.4 - 3.3 * Math.cos(dp) - 0.6 * Math.cos(2 * phase - dp) - 0.5 * Math.cos(2 * phase)

  np = 2 * Math::PI * normalize((inter - 2451565.2) / 27.212220817)
  la = 5.1 * Math.sin(np)

  rp = normalize((inter - 2451555.8 ) / 27.321582241)
  lo = 360 * rp + 6.3 * Math.sin(dp) + 1.3 * Math.sin(2 * phase - dp) + 0.7 * Math.sin(2 * phase)
  @ll = [la, lo]
end

calc_phase(p) click to toggle source

# File lib/moon_calc.rb, line 26
def calc_phase(p)
  case p
  when 0       then :new
  when 1..6    then :waxing_crescent
  when 7..9    then :first_quarter
  when 10..12  then :waxing_gibbous
  when 13..16  then :full
  when 17..20  then :waning_gibbous
  when 21..24  then :last_quarter
  when 25..28  then :waning_crescent
  else :new
  end
end

do_calc() click to toggle source

# File lib/moon_calc.rb, line 53
def do_calc
  c_phase = 29.530588853
  t_year = @epoch.year - ((12 - @epoch.month)/10).to_i
  t_month = (@epoch.month + 9) % 12

  t1 = (365.25 * (t_year + 4712)).to_i
  t2 = (30.6 * t_month + 0.5).to_i
  t3 = (((t_year / 100.0) + 49.0) * 0.75).to_i - 38
  inter = t1 + t2 + @epoch.day + 59
  inter -= t3 if inter > 2299160
  phase = normalize((inter - 2451550.1) / c_phase)
  res = phase * c_phase;

  @days  = (res * 100).to_i / 100
  @icon  = res.to_i % 30
  @phase = calc_phase(@icon)
  calc_coords(inter, phase)
end

normalize(x) click to toggle source

# File lib/moon_calc.rb, line 72
def normalize(x)
  x %= 1
  x += 1 if x < 0
  x
end