Class: Astronoby::Sun

Inherits:
Object
  • Object
show all
Defined in:
lib/astronoby/bodies/sun.rb

Constant Summary collapse

SEMI_MAJOR_AXIS_IN_METERS = 
149_598_500_000
ANGULAR_DIAMETER = 
Angle.from_degrees(0.533128)
INTERPOLATION_FACTOR = 
24.07
TWILIGHTS = 
[
  CIVIL = :civil,
  NAUTICAL = :nautical,
  ASTRONOMICAL = :astronomical
].freeze
TWILIGHT_ANGLES = 
{
  CIVIL => Angle.from_degrees(96),
  NAUTICAL => Angle.from_degrees(102),
  ASTRONOMICAL => Angle.from_degrees(108)
}.freeze
PERIODS_OF_THE_DAY = 
[
  MORNING = :morning,
  EVENING = :evening
].freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(time:) ⇒ Sun

Returns a new instance of Sun.

Parameters:

  • time (Time) —

    Considered time



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# File 'lib/astronoby/bodies/sun.rb', line 73

def initialize(time:)
  @time = time
end

Instance Attribute Details

#time ⇒ Object (readonly)

Returns the value of attribute time.



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# File 'lib/astronoby/bodies/sun.rb', line 26

def time
  @time
end

Class Method Details

.equation_of_time(date_or_time:) ⇒ Integer

Returns Equation of time in seconds.

Parameters:

  • date_or_time (Date, Time) —

    Requested date

Returns:

  • (Integer) —

    Equation of time in seconds



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# File 'lib/astronoby/bodies/sun.rb', line 36

def self.equation_of_time(date_or_time:)
  noon = Time.utc(date_or_time.year, date_or_time.month, date_or_time.day, 12)
  time = date_or_time.is_a?(Time) ? date_or_time : noon
  epoch = Epoch.from_time(time)
  sun = new(time: time)
  right_ascension = sun
    .apparent_ecliptic_coordinates
    .to_apparent_equatorial(epoch: epoch)
    .right_ascension
  t = (epoch - Epoch::J2000) / Constants::DAYS_PER_JULIAN_MILLENIA
  l0 = (280.4664567 +
    360_007.6982779 * t +
    0.03032028 * t**2 +
    t**3 / 49_931 -
    t**4 / 15_300 -
    t**5 / 2_000_000) % Constants::DEGREES_PER_CIRCLE
  nutation = Nutation.for_ecliptic_longitude(epoch: epoch)
  obliquity = TrueObliquity.for_epoch(epoch)

  (
    Angle
     .from_degrees(
       l0 -
       Constants::EQUATION_OF_TIME_CONSTANT -
       right_ascension.degrees +
       nutation.degrees * obliquity.cos
     ).hours * Constants::SECONDS_PER_HOUR
  ).round
end

Instance Method Details

#angular_size ⇒ Astronoby::Angle

Returns Apparent Sun’s angular size.

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 165

def angular_size
  Angle.from_degrees(
    ANGULAR_DIAMETER.degrees * distance_angular_size_factor
  )
end

#apparent_ecliptic_coordinates ⇒ Object 



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# File 'lib/astronoby/bodies/sun.rb', line 88

def apparent_ecliptic_coordinates
  nutation = Nutation.for_ecliptic_longitude(epoch: epoch)
  longitude_with_aberration = Aberration.for_ecliptic_coordinates(
    coordinates: true_ecliptic_coordinates,
    epoch: epoch
  ).longitude
  apparent_longitude = nutation + longitude_with_aberration

  Coordinates::Ecliptic.new(
    latitude: Angle.zero,
    longitude: apparent_longitude
  )
end

#earth_distance ⇒ Numeric

Returns Earth-Sun distance in meters.

Returns:

  • (Numeric) —

    Earth-Sun distance in meters



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# File 'lib/astronoby/bodies/sun.rb', line 160

def earth_distance
  SEMI_MAJOR_AXIS_IN_METERS / distance_angular_size_factor
end

#epoch ⇒ Object 



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# File 'lib/astronoby/bodies/sun.rb', line 77

def epoch
  @epoch ||= Epoch.from_time(@time)
end

#horizontal_coordinates(latitude:, longitude:) ⇒ Astronoby::Coordinates::Horizontal

Computes the Sun’s horizontal coordinates

Parameters:

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 107

def horizontal_coordinates(latitude:, longitude:)
  apparent_ecliptic_coordinates
    .to_apparent_equatorial(epoch: epoch)
    .to_horizontal(time: @time, latitude: latitude, longitude: longitude)
end

#longitude_at_perigee ⇒ Astronoby::Angle

Returns Sun’s longitude at perigee.

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 190

def longitude_at_perigee
  Angle.from_degrees(
    (281.2208444 + 1.719175 * centuries + 0.000452778 * centuries**2) %
      Constants::DEGREES_PER_CIRCLE
  )
end

#observation_events(observer:) ⇒ Astronoby::Events::ObservationEvents

Returns Sun’s observation events.

Parameters:

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 115

def observation_events(observer:)
  today = @time.to_date
  leap_seconds = Util::Time.terrestrial_universal_time_delta(today)
  yesterday = today.prev_day
  yesterday_midnight_terrestrial_time =
    Time.utc(yesterday.year, yesterday.month, yesterday.day) - leap_seconds
  yesterday_epoch = Epoch.from_time(yesterday_midnight_terrestrial_time)
  today_midnight_terrestrial_time =
    Time.utc(today.year, today.month, today.day) - leap_seconds
  today_epoch = Epoch.from_time(today_midnight_terrestrial_time)
  tomorrow = today.next_day
  tomorrow_midnight_terrestrial_time =
    Time.utc(tomorrow.year, tomorrow.month, tomorrow.day) - leap_seconds
  tomorrow_epoch = Epoch.from_time(tomorrow_midnight_terrestrial_time)

  coordinates_of_the_previous_day = self.class
    .new(time: yesterday_midnight_terrestrial_time)
    .apparent_ecliptic_coordinates
    .to_apparent_equatorial(epoch: yesterday_epoch)
  coordinates_of_the_day = self.class
    .new(time: today_midnight_terrestrial_time)
    .apparent_ecliptic_coordinates
    .to_apparent_equatorial(epoch: today_epoch)
  coordinates_of_the_next_day = self.class
    .new(time: tomorrow_midnight_terrestrial_time)
    .apparent_ecliptic_coordinates
    .to_apparent_equatorial(epoch: tomorrow_epoch)

  Events::ObservationEvents.new(
    observer: observer,
    date: today,
    coordinates_of_the_previous_day: coordinates_of_the_previous_day,
    coordinates_of_the_day: coordinates_of_the_day,
    coordinates_of_the_next_day: coordinates_of_the_next_day,
    additional_altitude: Angle.from_degrees(angular_size.degrees / 2)
  )
end

#orbital_eccentricity ⇒ Astronoby::Angle

Returns Sun’s orbital eccentricity.

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 198

def orbital_eccentricity
  Angle.from_degrees(
    (0.01675104 - 0.0000418 * centuries - 0.000000126 * centuries**2) %
      Constants::DEGREES_PER_CIRCLE
  )
end

#true_anomaly ⇒ Astronoby::Angle

Returns Sun’s true anomaly.

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 172

def true_anomaly
  eccentric_anomaly = Util::Astrodynamics.eccentric_anomaly_newton_raphson(
    mean_anomaly,
    orbital_eccentricity.degrees,
    2e-06,
    10
  )

  tan = Math.sqrt(
    (1 + orbital_eccentricity.degrees) / (1 - orbital_eccentricity.degrees)
  ) * Math.tan(eccentric_anomaly.radians / 2)

  Angle.from_degrees(
    (Angle.atan(tan).degrees * 2) % Constants::DEGREES_PER_CIRCLE
  )
end

#true_ecliptic_coordinates ⇒ Object 



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# File 'lib/astronoby/bodies/sun.rb', line 81

def true_ecliptic_coordinates
  Coordinates::Ecliptic.new(
    latitude: Angle.zero,
    longitude: true_longitude
  )
end

#twilight_events(observer:) ⇒ Astronoby::Events::TwilightEvents

Returns Sun’s twilight events.

Parameters:

Returns:



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# File 'lib/astronoby/bodies/sun.rb', line 155

def twilight_events(observer:)
  Events::TwilightEvents.new(sun: self, observer: observer)
end