Class: MoonPhases

Inherits:
Object
  • Object
show all
Defined in:
lib/astro_calc/moon_phases.rb

Overview

Credits tingletech

Constant Summary collapse

YEAR_IN_DAYS = 
365.25
LIMIT_JULIAN_CALENDAR = 
2299160
JULIAN_DAYS_IN_MONTH = 
29.530588853

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(date = Date.today) ⇒ MoonPhases

Returns a new instance of MoonPhases.



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# File 'lib/astro_calc/moon_phases.rb', line 16

def initialize(date = Date.today)
  @date = date
  perform_calculations
end

Instance Attribute Details

#age ⇒ Object (readonly)

Returns the value of attribute age.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def age
  @age
end

#constellation ⇒ Object (readonly)

Returns the value of attribute constellation.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def constellation
  @constellation
end

#date ⇒ Object (readonly)

Returns the value of attribute date.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def date
  @date
end

#detailed_age ⇒ Object (readonly)

Returns the value of attribute detailed_age.



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# File 'lib/astro_calc/moon_phases.rb', line 13

def detailed_age
  @detailed_age
end

#detailed_constellation ⇒ Object (readonly)

Returns the value of attribute detailed_constellation.



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# File 'lib/astro_calc/moon_phases.rb', line 13

def detailed_constellation
  @detailed_constellation
end

#detailed_distance ⇒ Object (readonly)

Returns the value of attribute detailed_distance.



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# File 'lib/astro_calc/moon_phases.rb', line 13

def detailed_distance
  @detailed_distance
end

#detailed_position ⇒ Object (readonly)

Returns the value of attribute detailed_position.



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# File 'lib/astro_calc/moon_phases.rb', line 13

def detailed_position
  @detailed_position
end

#distance ⇒ Object (readonly)

Returns the value of attribute distance.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def distance
  @distance
end

#latitude ⇒ Object (readonly)

Returns the value of attribute latitude.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def latitude
  @latitude
end

#longitude ⇒ Object (readonly)

Returns the value of attribute longitude.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def longitude
  @longitude
end

#magnitude ⇒ Object (readonly)

for svg



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# File 'lib/astro_calc/moon_phases.rb', line 11

def magnitude
  @magnitude
end

#phase ⇒ Object (readonly)

Returns the value of attribute phase.



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# File 'lib/astro_calc/moon_phases.rb', line 10

def phase
  @phase
end

#sweep ⇒ Object (readonly)

for svg



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# File 'lib/astro_calc/moon_phases.rb', line 11

def sweep
  @sweep
end

Instance Method Details

#normalize(value) ⇒ Float

Normalizes the value to be in the range 0..1

Parameters:

  • value (Float) —

    the value to normalize

Returns:

  • (Float) —

    the normalized value



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# File 'lib/astro_calc/moon_phases.rb', line 110

def normalize(value)
  value -= value.floor 
  value += 1 if value < 0
  value
end

#perform_calculations ⇒ Object 



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# File 'lib/astro_calc/moon_phases.rb', line 21

def perform_calculations
  year  = @date.year
  month = @date.month
  day   = @date.day

  #calculate the Julian date at 12h UT
  y = year - ((12 - month) / 10.0).floor
  m = month + 9 
  m = m - 12 if m >= 12
  
  k1 = (YEAR_IN_DAYS * (y + 4712)).floor
  k2 = (30.6 * m + 0.5 ).floor
  k3 = (((y / 100) + 49) * 0.75).floor - 38
  
  julian_day = k1 + k2 + day + 59                                    # for Julian calendar
  julian_day = julian_day - k3 if julian_day > LIMIT_JULIAN_CALENDAR # for Gregorian calendar
      
  #calculate moons age in Julian days
  i_phase  = normalize((julian_day - 2451550.1 ) / JULIAN_DAYS_IN_MONTH)
  @age = i_phase * JULIAN_DAYS_IN_MONTH
  
  @phase = case @age
    when 1.84566..5.53699 then "waxing crescent"
    when 5.53669..9.22831 then "first quarter"
    when 9.22831..12.91963 then "waxing gibbous"
    when 12.91963..16.61096 then "full moon"
    when 16.61096..20.30228 then "waning gibbous"
    when 20.30228..20.30228 then "last quarter"
    when 20.30228..27.68493 then "waning crescent"
    else "new moon"
  end
  
  #convert phase to radians
  i_phase_radians = i_phase * 2 * Math::PI  

  #calculate moon's distance
  distance_phase = 2 * Math::PI * normalize((julian_day - 2451562.2 ) / 27.55454988)
  @distance = 60.4 - 3.3 * Math.cos(distance_phase) - 0.6 * Math.cos(2 * i_phase_radians - distance_phase) - 0.5 * Math.cos(2 * i_phase_radians)

  #calculate moon's ecliptic latitude
  normal = 2 * Math::PI * normalize((julian_day - 2451565.2) / 27.212220817)
  @latitude = (5.1 * Math.sin(normal)).round(3)

  #calculate moon's ecliptic longitude
  real_phase = normalize((julian_day - 2451555.8) / 27.321582241)
  @longitude = (360 * real_phase + 6.3 * Math::sin(distance_phase) + 1.3 * Math.sin(2 * i_phase_radians - distance_phase) + 0.7 * Math.sin(2 * i_phase_radians)).round(3)

  @constellation = case @longitude
    when 33.18..51.16 then "Aries"
    when 51.16..93.44 then "Taurus"
    when 93.44..119.48 then "Gemini"
    when 119.48..135.30 then "Cancer"
    when 135.30..173.34 then "Leo"
    when 173.34..224.17 then "Virgo"
    when 224.17..242.57 then "Libra"
    when 242.57..271.26 then "Scorpio"
    when 271.26..302.49 then "Sagittarius"
    when 302.49..311.72 then "Capricorn"
    when 311.72..348.58 then "Aquarius"
    else "Pisces"
  end

  # the "sweep-flag" and the direction of movement change every quarter moon
  # zero and one are both new moon; 0.50 is full moon    
  case i_phase
  when 0.25..0.50 then
    @sweep     = [0, 0];
    @magnitude = 20 * (i_phase - 0.25) * 4
  when 0.50..0.75 then
    @sweep     = [1, 1];
    @magnitude = 20 - 20 * (i_phase - 0.50) * 4
  when 0.75..1.00 then
    @sweep     = [0, 1];
    @magnitude = 20 * (i_phase - 0.75) * 4
  else 
    @sweep     = [1, 0];
    @magnitude = 20 - 20 * i_phase   * 4
  end

  @detailed_position      = "Ecliptic position : λ #{@longitude} - β #{@latitude}"
  @detailed_age           = "Current cycle age #{(@age).round(2)} days"
  @detailed_distance      = "Distance is #{(@distance).round(2)} earth radii"
  @detailed_constellation = "The #{@phase} moon is in #{@constellation}"    
end

#svg ⇒ String

Calculates the magnification for a given telescope and eyepiece

Returns:

  • (String) —

    the SVG output



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# File 'lib/astro_calc/moon_phases.rb', line 135

def svg
  output = ""
  output << "<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100% 100%' version='1.1' id='moon_phase'>"
  output << "<path d='m100,0 a20,20 0 1,1 0,150 a20,20 0 1,1 0,-150' class='moon_back'></path>"
  output << "<image xlink:href='moon.jpg; x='0' y='0' height='200px' width='200px'/>"
  output << "<path d='m100,0 a#{@magnitude.round(2)},20 0 1,#{@sweep[0]} 0,150 a20,20 0 1,#{@sweep[1]} 0,-150' class='moon'></path>"
  output << "</svg>"
  output.html_safe
end

#unicode ⇒ String

Provides the unicode characters for the moon phase

Returns:

  • (String) —

    the unicode string showing the moon phase



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# File 'lib/astro_calc/moon_phases.rb', line 119

def unicode  
  case @phase 
    when 0.0625..0.1875 then "🌒"
    when 0.1875..0.3125 then "🌓"
    when 0.3125..0.4375 then "🌔"
    when 0.4375..0.5625 then "🌕"
    when 0.5625..0.6875 then "🌖"
    when 0.6875..0.8125 then "🌗"
    when 0.8125..0.9375 then "🌘"
    else "🌑"      
  end
end