Class: Astronoby::Moon

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

Constant Summary collapse

SEMIDIAMETER_VARIATION = 
0.7275
MEAN_GEOCENTRIC_DISTANCE = 
Astronoby::Distance.from_meters(385_000_560)

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(time:) ⇒ Moon

Returns a new instance of Moon.



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# File 'lib/astronoby/bodies/moon.rb', line 21

def initialize(time:)
  @time = time
end

Class Method Details

.monthly_phase_events(year:, month:) ⇒ Array<Astronoby::MoonPhase>

Returns Moon phases for the requested year.

Parameters:

  • year (Integer) —

    Requested year

  • month (Integer) —

    Requested month

Returns:



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# File 'lib/astronoby/bodies/moon.rb', line 17

def self.monthly_phase_events(year:, month:)
  Events::MoonPhases.phases_for(year: year, month: month)
end

Instance Method Details

#apparent_ecliptic_coordinates ⇒ Astronoby::Coordinates::Ecliptic

Returns Apparent ecliptic coordinates of the Moon.

Returns:



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# File 'lib/astronoby/bodies/moon.rb', line 27

def apparent_ecliptic_coordinates
  @ecliptic_coordinates ||= begin
    latitude = Astronoby::Angle.from_degrees(
      (latitude_terms + additive_latitude_terms) *
        EphemerideLunaireParisienne::DEGREES_UNIT
    )

    longitude = mean_longitude + Astronoby::Angle.from_degrees(
      (longitude_terms + additive_longitude_terms) *
        EphemerideLunaireParisienne::DEGREES_UNIT
    ) + nutation

    Coordinates::Ecliptic.new(
      latitude: latitude,
      longitude: longitude
    )
  end
end

#apparent_equatorial_coordinates ⇒ Astronoby::Coordinates::Equatorial

Returns Apparent geocentric equatorial coordinates of the Moon.

Returns:



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# File 'lib/astronoby/bodies/moon.rb', line 54

def apparent_equatorial_coordinates
  @apparent_equatorial_coordinates ||=
    apparent_ecliptic_coordinates
      .to_apparent_equatorial(epoch: Epoch.from_time(@time))
end

#argument_of_latitude ⇒ Angle

Returns Moon’s argument of latitude.

Returns:

  • (Angle) —

    Moon’s argument of latitude



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# File 'lib/astronoby/bodies/moon.rb', line 122

def argument_of_latitude
  @argument_of_latitude ||= Angle.from_degrees(
    (
      93.2720950 +
      483202.0175233 * elapsed_centuries -
      0.0036539 * elapsed_centuries**2 -
      elapsed_centuries**3 / 3526000
    ) % 360
  )
end

#distance ⇒ Astronoby::Distance

Returns Distance between the Earth and the Moon centers.

Returns:



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# File 'lib/astronoby/bodies/moon.rb', line 76

def distance
  @distance ||= Astronoby::Distance.from_meters(
    (MEAN_GEOCENTRIC_DISTANCE.meters + distance_terms).round
  )
end

#horizontal_coordinates(observer:) ⇒ Object 



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# File 'lib/astronoby/bodies/moon.rb', line 60

def horizontal_coordinates(observer:)
  apparent_topocentric_equatorial_coordinates =
    Astronoby::GeocentricParallax.for_equatorial_coordinates(
      observer: observer,
      time: @time,
      coordinates: apparent_equatorial_coordinates,
      distance: distance
    )

  apparent_topocentric_equatorial_coordinates.to_horizontal(
    observer: observer,
    time: @time
  )
end

#illuminated_fraction ⇒ Float

Returns Moon’s illuminated fraction.

Returns:

  • (Float) —

    Moon’s illuminated fraction



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# File 'lib/astronoby/bodies/moon.rb', line 166

def illuminated_fraction
  @illuminated_fraction ||= (1 + phase_angle.cos) / 2
end

#mean_anomaly ⇒ Angle

Returns Moon’s mean anomaly.

Returns:

  • (Angle) —

    Moon’s mean anomaly



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# File 'lib/astronoby/bodies/moon.rb', line 109

def mean_anomaly
  @mean_anomaly ||= Angle.from_degrees(
    (
      134.9633964 +
      477198.8675055 * elapsed_centuries +
      0.0087414 * elapsed_centuries**2 +
      elapsed_centuries**3 / 69699 -
      elapsed_centuries**4 / 14712000
    ) % 360
  )
end

#mean_elongation ⇒ Angle

Returns Moon’s mean elongation.

Returns:

  • (Angle) —

    Moon’s mean elongation



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# File 'lib/astronoby/bodies/moon.rb', line 96

def mean_elongation
  @mean_elongation ||= Angle.from_degrees(
    (
      297.8501921 +
      445267.1114034 * elapsed_centuries -
      0.0018819 * elapsed_centuries**2 +
      elapsed_centuries**3 / 545868 -
      elapsed_centuries**4 / 113065000
    ) % 360
  )
end

#mean_longitude ⇒ Angle

Returns Moon’s mean longitude.

Returns:

  • (Angle) —

    Moon’s mean longitude



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# File 'lib/astronoby/bodies/moon.rb', line 83

def mean_longitude
  @mean_longitude ||= Angle.from_degrees(
    (
      218.3164477 +
      481267.88123421 * elapsed_centuries -
      0.0015786 * elapsed_centuries**2 +
      elapsed_centuries**3 / 538841 -
      elapsed_centuries**4 / 65194000
    ) % 360
  )
end

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

Returns Moon’s observation events.

Parameters:

Returns:



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

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
  today_midnight_terrestrial_time =
    Time.utc(today.year, today.month, today.day) - leap_seconds
  tomorrow = today.next_day
  tomorrow_midnight_terrestrial_time =
    Time.utc(tomorrow.year, tomorrow.month, tomorrow.day) - leap_seconds

  coordinates_of_the_previous_day = self.class
    .new(time: yesterday_midnight_terrestrial_time)
    .apparent_equatorial_coordinates
  coordinates_of_the_day = self.class
    .new(time: today_midnight_terrestrial_time)
    .apparent_equatorial_coordinates
  coordinates_of_the_next_day = self.class
    .new(time: tomorrow_midnight_terrestrial_time)
    .apparent_equatorial_coordinates
  additional_altitude = -Angle.from_degrees(
    SEMIDIAMETER_VARIATION *
      GeocentricParallax.angle(distance: distance).degrees
  )

  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: additional_altitude
  )
end

#phase_angle ⇒ Angle

Returns Moon’s phase angle.

Returns:

  • (Angle) —

    Moon’s phase angle



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# File 'lib/astronoby/bodies/moon.rb', line 140

def phase_angle
  @phase_angle ||= begin
    sun_apparent_equatorial_coordinates = sun
      .apparent_ecliptic_coordinates
      .to_apparent_equatorial(epoch: Epoch.from_time(@time))
    moon_apparent_equatorial_coordinates = apparent_equatorial_coordinates
    geocentric_elongation = Angle.acos(
      sun_apparent_equatorial_coordinates.declination.sin *
        moon_apparent_equatorial_coordinates.declination.sin +
        sun_apparent_equatorial_coordinates.declination.cos *
        moon_apparent_equatorial_coordinates.declination.cos *
        (
          sun_apparent_equatorial_coordinates.right_ascension -
          moon_apparent_equatorial_coordinates.right_ascension
        ).cos
    )

    term1 = sun.earth_distance.km * geocentric_elongation.sin
    term2 = distance.km - sun.earth_distance.km * geocentric_elongation.cos
    angle = Angle.atan(term1 / term2)
    Astronoby::Util::Trigonometry
      .adjustement_for_arctangent(term1, term2, angle)
  end
end