module BBS::Season::Clock

The class methods of a Season for the clock and the sky: the offset of a time zone (Season.offset), EU summer time (Season.eu_summer?) and the sunrise and sunset of a day (Season.sun).

Constants

DECLINATION: The sun’s declination in radians as a NOAA series over the fractional year: the constant and the [cos, sin] of each harmonic.
EQUATION_OF_TIME: The equation of time (over 229.18 minutes) as a NOAA series.

Public Instance Methods

eu_summer? (utc)

Source

# File lib/bbs/season/clock.rb, line 30
def eu_summer?(utc)
  year = utc.year
  utc >= Time.utc(year, 3, last_sunday(year, 3), 1) && utc < Time.utc(year, 10, last_sunday(year, 10), 1)
end

Whether EU summer time is in force at utc: from 01:00 UTC on the last Sunday of March to 01:00 UTC on the last Sunday of October.

last_sunday (year, month)

Source

# File lib/bbs/season/clock.rb, line 36
def last_sunday(year, month)
  last = Date.new(year, month, -1)
  last.day - last.wday
end

The day of the month of the last Sunday of month in year.

offset (tz, utc)

Source

# File lib/bbs/season/clock.rb, line 17
def offset(tz, utc)
  return tz.utc_offset_at(utc) if tz.respond_to?(:utc_offset_at)
  return tz.period_for_utc(utc).utc_total_offset if tz.respond_to?(:period_for_utc)

  name = tz.to_s
  return fixed_offset(name) if OFFSET_RE.match?(name)
  return zone_offset(name, utc) if ZONES.key?(name)

  tzinfo(name).period_for_utc(utc).utc_total_offset
end

The offset from UTC in seconds of time zone tz (see Season.now) at utc, a Time. Raises ArgumentError for a zone it does not know.

sun (date, latitude, longitude)

Source

# File lib/bbs/season/clock.rb, line 44
def sun(date, latitude, longitude)
  g  = 2 * Math::PI / 365 * (date.yday - 1)
  ha = hour_angle(latitude * Math::PI / 180, series(DECLINATION, g))
  return [nil, nil] unless ha

  [ha, -ha].map { |h| 720 - (4 * (longitude + h)) - (229.18 * series(EQUATION_OF_TIME, g)) }
end

Sunrise and sunset on date (a Date) at latitude, longitude, in minutes after midnight UTC (Floats): [rise, set], or [nil, nil] for polar day or night. The NOAA approximation.