Class: Astronoby::Coordinates::Horizontal

Inherits:
Object
  • Object
show all
Defined in:
lib/astronoby/coordinates/horizontal.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(azimuth:, altitude:, observer:) ⇒ Horizontal

Returns a new instance of Horizontal.



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# File 'lib/astronoby/coordinates/horizontal.rb', line 8

def initialize(
  azimuth:,
  altitude:,
  observer:
)
  @azimuth = azimuth
  @altitude = altitude
  @observer = observer
end

Instance Attribute Details

#altitude ⇒ Object (readonly)

Returns the value of attribute altitude.



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# File 'lib/astronoby/coordinates/horizontal.rb', line 6

def altitude
  @altitude
end

#azimuth ⇒ Object (readonly)

Returns the value of attribute azimuth.



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# File 'lib/astronoby/coordinates/horizontal.rb', line 6

def azimuth
  @azimuth
end

#observer ⇒ Object (readonly)

Returns the value of attribute observer.



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# File 'lib/astronoby/coordinates/horizontal.rb', line 6

def observer
  @observer
end

Instance Method Details

#to_equatorial(time:) ⇒ Object 



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# File 'lib/astronoby/coordinates/horizontal.rb', line 18

def to_equatorial(time:)
  t0 = @altitude.sin * latitude.sin +
    @altitude.cos * latitude.cos * @azimuth.cos

  declination = Angle.asin(t0)

  t1 = @altitude.sin - latitude.sin * declination.sin

  hour_angle_degrees = Angle
    .acos(t1 / (latitude.cos * declination.cos))
    .degrees

  if @azimuth.sin.positive?
    hour_angle_degrees = Angle
      .from_degrees(Constants::DEGREES_PER_CIRCLE - hour_angle_degrees)
      .degrees
  end

  hour_angle_hours = Angle.from_degrees(hour_angle_degrees).hours
  lst = GreenwichSiderealTime
    .from_utc(time.utc)
    .to_lst(longitude: longitude)
  right_ascension_decimal = lst.time - hour_angle_hours

  if right_ascension_decimal.negative?
    right_ascension_decimal += Constants::HOURS_PER_DAY
  end

  right_ascension = Angle.from_hours(right_ascension_decimal)

  Equatorial.new(
    right_ascension: right_ascension,
    declination: declination
  )
end