Class: Astronoby::Refraction

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

Constant Summary collapse

DEFAULT_PRESSURE = 
1000
DEFAULT_TEMPERATURE = 
25

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(coordinates, pressure, temperature) ⇒ Refraction

Returns a new instance of Refraction.



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# File 'lib/astronoby/refraction.rb', line 16

def initialize(coordinates, pressure, temperature)
  @coordinates = coordinates
  @pressure = pressure
  @temperature = temperature
end

Class Method Details

.for_horizontal_coordinates(coordinates:, pressure: DEFAULT_PRESSURE, temperature: DEFAULT_TEMPERATURE) ⇒ Object 



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# File 'lib/astronoby/refraction.rb', line 8

def self.for_horizontal_coordinates(
  coordinates:,
  pressure: DEFAULT_PRESSURE,
  temperature: DEFAULT_TEMPERATURE
)
  new(coordinates, pressure, temperature).refract
end

Instance Method Details

#refract ⇒ Object

Source:

Title: Practical Astronomy with your Calculator or Spreadsheet
Authors: Peter Duffett-Smith and Jonathan Zwart
Edition: Cambridge University Press
Chapter: 37 - Refraction



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# File 'lib/astronoby/refraction.rb', line 27

def refract
  altitude_in_degrees = @coordinates.altitude.degrees

  refraction_angle = Angle.as_degrees(
    if altitude_in_degrees > 15
      zenith_angle = Angle.as_degrees(90 - @coordinates.altitude.degrees)
      0.00452 * @pressure * zenith_angle.tan / (273 + @temperature)
    else
      (
        @pressure *
        (
          0.1594 +
          0.0196 * altitude_in_degrees +
          0.00002 * altitude_in_degrees * altitude_in_degrees
        )
      )./(
        (273 + @temperature) *
        (
          1 +
          0.505 * altitude_in_degrees +
          0.0845 * altitude_in_degrees * altitude_in_degrees
        )
      )
    end
  )

  Coordinates::Horizontal.new(
    azimuth: @coordinates.azimuth,
    altitude: @coordinates.altitude + refraction_angle,
    latitude: @coordinates.latitude,
    longitude: @coordinates.longitude
  )
end