Class: Astronoby::Apparent

Inherits:
ReferenceFrame show all
Defined in:
lib/astronoby/reference_frames/apparent.rb

Overview

Apparent reference frame. Represents a body’s geocentric position as it appears from Earth, corrected for aberration, precession, and nutation.

Instance Attribute Summary

Attributes inherited from ReferenceFrame

#center, #instant, #position, #target_body, #velocity

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from ReferenceFrame

#distance, #equatorial, #initialize, #separation_from

Constructor Details

This class inherits a constructor from Astronoby::ReferenceFrame

Class Method Details

.build_from_astrometric(instant:, target_astrometric:, earth_geometric:, target_body:) ⇒ Astronoby::Apparent

Builds an apparent frame from an astrometric frame by applying aberration in GCRS, then rotating by nutation * precession (with ICRS frame bias).

Parameters:

Returns:



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# File 'lib/astronoby/reference_frames/apparent.rb', line 17

def self.build_from_astrometric(
  instant:,
  target_astrometric:,
  earth_geometric:,
  target_body:
)
  position = target_astrometric.position
  velocity = target_astrometric.velocity
  precession_matrix = Precession.matrix_for(instant)
  nutation_matrix = Nutation.matrix_for(instant)

  corrected_position = Aberration.new(
    astrometric_position: position,
    observer_velocity: earth_geometric.velocity
  ).corrected_position

  # In theory, here we should also apply light deflection. However, so far
  # the deflection algorithm hasn't shown any significant changes to the
  # apparent position. Therefore, for now, we are saving some computation
  # time by not applying it, and we will investigate if the algorithm is
  # correct or if the deflection is indeed negligible.

  corrected_position = Distance.vector_from_meters(
    nutation_matrix * precession_matrix * corrected_position.map(&:m)
  )

  corrected_velocity = Velocity.vector_from_mps(
    nutation_matrix * precession_matrix * velocity.map(&:mps)
  )

  new(
    position: corrected_position,
    velocity: corrected_velocity,
    instant: instant,
    center: Center.geocentric,
    target_body: target_body
  )
end

Instance Method Details

#ecliptic ⇒ Astronoby::Coordinates::Ecliptic

Returns ecliptic coordinates at the current instant (true ecliptic and equinox of date).

Returns:



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# File 'lib/astronoby/reference_frames/apparent.rb', line 58

def ecliptic
  @ecliptic ||= begin
    return Coordinates::Ecliptic.zero if distance.zero?

    equatorial.to_ecliptic(
      instant: @instant,
      obliquity: TrueObliquity.at(@instant)
    )
  end
end