Class: Easter

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

Class Method Summary collapse

Class Method Details

.ascension_day(some_year = Time.now.year) ⇒ Object

Determines the date of Ascension Day for a given year.



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# File 'lib/easter.rb', line 82

def self.ascension_day(some_year=Time.now.year)
  easter(some_year) - 39
end

.ash_wednesday(some_year = Time.now.year) ⇒ Object

Determines the date of Ash Wednesday for a given year.



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# File 'lib/easter.rb', line 76

def self.ash_wednesday(some_year=Time.now.year)
  easter(some_year) - 46
end

.easter(some_year = Time.now.year) ⇒ Object 



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# File 'lib/easter.rb', line 26

def self.easter(some_year=Time.now.year)

  golden_number = (some_year % 19) + 1
  
  if some_year <= 1752 then
    # Julian calendar
    dominical_number = (some_year + (some_year / 4) + 5) % 7
    paschal_full_moon = (3 - (11 * golden_number) - 7) % 30
  else
    # Gregorian calendar
    dominical_number = (some_year + (some_year / 4) - (some_year / 100) + (some_year / 400)) % 7
    solar_correction = (some_year - 1600) / 100 - (some_year - 1600) / 400
    lunar_correction = (((some_year - 1400) / 100) * 8) / 25
    paschal_full_moon = (3 - 11 * golden_number + solar_correction - lunar_correction) % 30
  end
  
  dominical_number += 7 until dominical_number > 0 

  paschal_full_moon += 30 until paschal_full_moon > 0 
  paschal_full_moon -= 1 if paschal_full_moon == 29 or (paschal_full_moon == 28 and golden_number > 11)

  difference = (4 - paschal_full_moon - dominical_number) % 7
  difference += 7 if difference < 0 

  day_easter = paschal_full_moon + difference + 1
  
  if day_easter < 11 then
    # Easter occurs in March.
    return DateTime.new(y=some_year, m=3, d=day_easter + 21)
  else
    # Easter occurs in April.
    return DateTime.new(y=some_year, m=4, d=day_easter - 10)
  end
  
end

.good_friday(some_year = Time.now.year) ⇒ Object

Determine the date of Good Friday for a given year.



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# File 'lib/easter.rb', line 64

def self.good_friday(some_year=Time.now.year)
  easter(some_year) - 2
end

.palm_sunday(some_year = Time.now.year) ⇒ Object

Determine the date of Palm Sunday for a given year.



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# File 'lib/easter.rb', line 70

def self.palm_sunday(some_year=Time.now.year)
  easter(some_year) - 7
end

.pentecost(some_year = Time.now.year) ⇒ Object

Determines the date of Pentecost for a given year.



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# File 'lib/easter.rb', line 88

def self.pentecost(some_year=Time.now.year)
  easter(some_year) + 49
end