Class: Date

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

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.easter(year) ⇒ Object

:call-seq: 

Date::easter(year)    => easter_sunday_Date

Return the Date upon which Easter Sunday falls in year. The Gregorian calendar is used.



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# File 'lib/date_easter.rb', line 48

def self.easter(year) 
  unless year.is_a? Numeric
    raise TypeError, "year must be Numeric" 
  end

  if year < 1583 
    raise ArgumentError, "Years before 1583 not supported"  
  elsif year > 4099
    raise ArgumentError, "Years after 4099 not supported"  
  end

  golden_number     = (year % 19) + 1
  century           = (year / 100) + 1
  julian_epact      = (11 * (golden_number -1)) % 30 
  solar_correction  = (3 * century) / 4
  lunar_correction  = ((8 * century) + 5) / 25

  gregorian_epact   = 
      (julian_epact - solar_correction + lunar_correction + 8) % 30

  days_fm_ve_to_pfm = (23 - gregorian_epact) % 30

  if gregorian_epact == 24 or gregorian_epact == 25 && golden_number > 11
    days_fm_ve_to_pfm -= 1 
  end

  vernal_equinox    = Date.new(year, 3, 21) 
  paschal_full_moon = vernal_equinox + days_fm_ve_to_pfm

  days_to_sunday    = 7 - paschal_full_moon.wday

  easter_sunday     = paschal_full_moon + days_to_sunday
end

Instance Method Details

#easter ⇒ Object

:call-seq: 

ref.easter()    => easter_sunday_Date

Return the Date of Easter Sunday for the year in which ref falls. The Gregorian calendar is used.



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

def easter
  Date::easter(self.year)
end