Class: Astronoby::MoonPhysicalEphemeris

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

Overview

Computes the ephemeris for physical observations of the Moon: the total (optical + physical) libration in longitude and latitude, and the position angle of the Moon’s axis of rotation.

Source:

Title: Astronomical Algorithms
Author: Jean Meeus
Edition: 2nd edition
Chapter: 53 - Ephemeris for Physical Observations of the Moon

Constant Summary collapse

INCLINATION =

Inclination of the mean lunar equator to the ecliptic

Angle.from_degrees(1.54242)

Instance Method Summary collapse

Constructor Details

#initialize(moon) ⇒ MoonPhysicalEphemeris

Returns a new instance of MoonPhysicalEphemeris.

Parameters:



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# File 'lib/astronoby/moon_physical_ephemeris.rb', line 18

def initialize(moon)
  @moon = moon
  @instant = moon.instant
end

Instance Method Details

#libration ⇒ Astronoby::Libration

Returns the total libration in longitude and latitude.

Returns:



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# File 'lib/astronoby/moon_physical_ephemeris.rb', line 25

def libration
  Libration.new(
    longitude: Angle.from_degrees(libration_in_longitude),
    latitude: Angle.from_degrees(libration_in_latitude)
  )
end

#position_angle_of_axis ⇒ Astronoby::Angle

Returns the position angle of the Moon’s axis of rotation, measured eastward from the north point of the disk.

Returns:

  • (Astronoby::Angle) —

    the position angle of the Moon’s axis of rotation, measured eastward from the north point of the disk



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# File 'lib/astronoby/moon_physical_ephemeris.rb', line 34

def position_angle_of_axis
  i_rho = INCLINATION + Angle.from_degrees(rho)
  v = ascending_node +
    nutation_in_longitude +
    Angle.from_degrees(sigma / INCLINATION.sin)

  x = i_rho.sin * v.sin
  y = i_rho.sin * v.cos * obliquity.cos - i_rho.cos * obliquity.sin
  omega = Math.atan2(x, y)

  Angle.from_radians(
    Math.asin(
      Math.sqrt(x * x + y * y) *
        Math.cos(right_ascension.radians - omega) /
        Angle.from_degrees(libration_in_latitude).cos
    )
  )
end