Sunrise and sunset

sun.rb

#!/usr/bin/env ruby
# -- encoding: utf-8 --

module Astronomy

  # Floor as function
  def floor x
    x.floor
  end

  # Defining of trigonomtetrical functions in degrees
  def self.def_trig *func
    func.collect! { |f| f.to_s }
    func.each do |f|
      module_eval <<-EVAL
      def #{f} x
        Math.#{f}(x*Math::PI/180)
      end
      def a#{f} x
        Math.a#{f}(x)*180/Math::PI
      end
      EVAL
    end
  end

  def_trig :sin, :cos, :tan

  OFFICIAL_ZENITH = 90.0 + 50.0/60.0 # 90°50'
  CIVIL_ZENITH = 96
  NAUTICAL_ZENITH = 102
  ASTRONOMICAL_ZENITH = 108

  # Algorithm see:
  # http://williams.best.vwh.net/sunrise_sunset_algorithm.htm
  # date: date of sunrise/sunset
  # latitude, longitude:   location for sunrise/sunset
  # zenith: Sun's zenith for sunrise/sunset
  #   offical      = 90 degrees 50'
  #   civil        = 96 degrees
  #   nautical     = 102 degrees
  #   astronomical = 108 degrees
  #
  # NOTE: longitude is positive for East and negative for West
  def sun_rise_set(date, latitude, longitude, zenith, rise_set)

    # 1. first sun_rise_set the day of the year

    n = date.yday

    # 2. convert the longitude to hour value and sun_rise_set an  approximate time

    lnghour = longitude / 15

    if rise_set == :rise
      # if rising time is desired:
      t = n + ((6 - lnghour) / 24)
    else
      # if setting time is desir.ed:
      t = n + ((18 - lnghour) / 24)
    end

    # 3. sun_rise_set the sun's mean anomaly

    m = (0.9856 * t) - 3.289

    # 4. sun_rise_set the sun's true longitude

    l = m + (1.916 * sin(m)) + (0.020 * sin(2 * m)) + 282.634

    # note: l potentially needs to be adjusted into the range [0,360) by
    # adding/subtracting 360
    l = l % 360

    # 5a. sun_rise_set the sun's right ascension

    ra = atan(0.91764 * tan(l))
    # note: ra potentially needs to be adjusted into the range [0,360) by
    # adding/subtracting 360
    ra = ra % 360

    # 5b. right ascension value needs to be in the same quadrant as l

    lquadrant  = (floor( l/90)) * 90
    raquadrant = (floor(ra/90)) * 90
    ra = ra + (lquadrant - raquadrant)

    # 5c. right ascension value needs to be converted into hours

    ra = ra / 15.0

    # 6. sun_rise_set the sun's declination

    sindec = 0.39782 * sin(l)
    cosdec = cos(asin(sindec))

    # 7a. sun_rise_set the sun's local hour angle

    cosh = (cos(zenith) - (sindec * sin(latitude))) / (cosdec * cos(latitude))

    if (cosh >  1)
      # the sun never rises on this location (on the specified date)
      return nil
    end
    if (cosh < -1)
      # the sun never sets on this location (on the specified date)
      return nil
    end

    # 7b. finish calculating h and convert into hours

    if rise_set == :rise
      # if if rising time is desired:
      h = 360 - acos(cosh)
    else
      #if setting time is desired:
      h = acos(cosh)
    end
    h = h / 15

    # 8. sun_rise_set local mean time of rising/setting

    t = h + ra - (0.06571 * t) - 6.622

    # 9. adjust back to utc

    ut = t - lnghour

    # note: ut potentially needs to be adjusted into the range [0,24) by
    # adding/subtracting 24
    ut = ut % 24

    Time.utc(date.year, date.month, date.day, ut.truncate,
             ((ut- ut.truncate).abs * 60).truncate)

    # 10. convert ut value to local time zone of latitude/longitude

    # localt = ut + localoffset

  end

end

#------------------------------------------------------------------------------

if __FILE__ == $0

  if ARGV.length != 2
    puts "Aufruf: ruby sun.rb [geogr. Breite] [geogr. Länge]"
    puts "  z.B.: ruby sun.rb 53.09 8.13"
    exit -1
  end

  lat, long = ARGV[0..1].collect{ |arg| arg.to_f }

  include Astronomy

  # Redefining of to_s
  class Time
    def to_s
      l = self.localtime
      "%02d:%02d (%s)" %  [l.hour, l.min, l.zone]
    end
  end

  today = Time.new

  puts "=" * 36

  time = sun_rise_set(today, lat, long, ASTRONOMICAL_ZENITH, :rise)
  puts "Astronomische Dämmerung: #{time}"

  time = sun_rise_set(today, lat, long, NAUTICAL_ZENITH, :rise)
  puts "Nautische Dämmerung:     #{time}"

  time = sun_rise_set(today, lat, long, CIVIL_ZENITH, :rise)
  puts "Bürgerliche Dämmerung:   #{time}"

  time = sun_rise_set(today, lat, long, OFFICIAL_ZENITH, :rise)
  puts "Sonnenaufgang:           #{time}"

  puts "-" * 36

  time = sun_rise_set(today, lat, long, OFFICIAL_ZENITH, :set)
  puts "Sonnenuntergang:         #{time}"

  time = sun_rise_set(today, lat, long, CIVIL_ZENITH, :set)
  puts "Bürgerliche Dämmerung:   #{time}"

  time = sun_rise_set(today, lat, long, NAUTICAL_ZENITH, :set)
  puts "Nautische Dämmerung:     #{time}"

  time = sun_rise_set(today, lat, long, ASTRONOMICAL_ZENITH, :set)
  puts "Astronomische Dämmerung: #{time}"

  puts "=" * 36

end