Class: Astronoby::MeanObliquity

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

Overview

Computes the mean obliquity of the ecliptic using the IAU 2006 P03 model.

Constant Summary collapse

EPOCH_OF_REFERENCE =

Source:

IAU resolution in 2006 in favor of the P03 astronomical model
https://syrte.obspm.fr/iau2006/aa03_412_P03.pdf

JulianDate::DEFAULT_EPOCH
OBLIQUITY_OF_REFERENCE = 
23.4392794

Class Method Summary collapse

Class Method Details

.at(instant) ⇒ Astronoby::Angle

Computes the mean obliquity of the ecliptic at the given instant.

Parameters:

Returns:



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# File 'lib/astronoby/mean_obliquity.rb', line 20

def self.at(instant)
  return obliquity_of_reference if instant.julian_date == EPOCH_OF_REFERENCE

  t = Rational(
    instant.julian_date - EPOCH_OF_REFERENCE,
    Constants::DAYS_PER_JULIAN_CENTURY
  )

  epsilon0 = obliquity_of_reference_in_arcseconds
  c1 = -46.836769
  c2 = -0.0001831
  c3 = 0.00200340
  c4 = -0.000000576
  c5 = -0.0000000434

  Angle.from_degree_arcseconds(
    epsilon0 + t * (c1 + t * (c2 + t * (c3 + t * (c4 + t * c5))))
  )
end

.obliquity_of_reference ⇒ Astronoby::Angle

Returns the mean obliquity at the reference epoch (J2000.0).

Returns:



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# File 'lib/astronoby/mean_obliquity.rb', line 42

def self.obliquity_of_reference
  Angle.from_degree_arcseconds(obliquity_of_reference_in_arcseconds)
end

.obliquity_of_reference_in_arcseconds ⇒ Float

Returns the mean obliquity at J2000.0 in arcseconds.

Returns:

  • (Float) —

    the mean obliquity at J2000.0 in arcseconds



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# File 'lib/astronoby/mean_obliquity.rb', line 47

def self.obliquity_of_reference_in_arcseconds
  84381.406
end