Treat true and mean obliquity as angles

lib/astronoby/coordinates/ecliptic.rb

@@ -17,18 +17,18 @@ def initialize(latitude:, longitude:)
       #  Chapter: 4 - Orbits and Coordinate Systems
       def to_equatorial(epoch:)
         mean_obliquity = MeanObliquity.for_epoch(epoch)
-        obliquity = mean_obliquity.value
 
         y = Angle.as_radians(
-          @longitude.sin * obliquity.cos - @latitude.tan * obliquity.sin
+          @longitude.sin * mean_obliquity.cos -
+          @latitude.tan * mean_obliquity.sin
         )
         x = Angle.as_radians(@longitude.cos)
         r = Angle.atan(y.radians / x.radians)
         right_ascension = Util::Trigonometry.adjustement_for_arctangent(y, x, r)
 
         declination = Angle.asin(
-          @latitude.sin * obliquity.cos +
-          @latitude.cos * obliquity.sin * @longitude.sin
+          @latitude.sin * mean_obliquity.cos +
+          @latitude.cos * mean_obliquity.sin * @longitude.sin
         )
 
         Equatorial.new(

lib/astronoby/coordinates/equatorial.rb

@@ -58,19 +58,18 @@ def to_horizontal(time:, latitude:, longitude:)
       #  Chapter: 4 - Orbits and Coordinate Systems
       def to_ecliptic(epoch:)
         mean_obliquity = MeanObliquity.for_epoch(epoch)
-        obliquity = mean_obliquity.value
 
         y = Angle.as_radians(
-          @right_ascension.sin * obliquity.cos +
-            @declination.tan * obliquity.sin
+          @right_ascension.sin * mean_obliquity.cos +
+          @declination.tan * mean_obliquity.sin
         )
         x = Angle.as_radians(@right_ascension.cos)
         r = Angle.atan(y.radians / x.radians)
         longitude = Util::Trigonometry.adjustement_for_arctangent(y, x, r)
 
         latitude = Angle.asin(
-          @declination.sin * obliquity.cos -
-          @declination.cos * obliquity.sin * @right_ascension.sin
+          @declination.sin * mean_obliquity.cos -
+          @declination.cos * mean_obliquity.sin * @right_ascension.sin
         )
 
         Ecliptic.new(

lib/astronoby/mean_obliquity.rb

@@ -11,34 +11,22 @@ class MeanObliquity
     EPOCH_OF_REFERENCE = Epoch::DEFAULT_EPOCH
     OBLIQUITY_OF_REFERENCE = 23.4392794
 
-    def initialize(obliquity)
-      @obliquity = obliquity
-    end
-
     def self.for_epoch(epoch)
-      if epoch == EPOCH_OF_REFERENCE
-        return new(obliquity_of_reference)
-      end
+      return obliquity_of_reference if epoch == EPOCH_OF_REFERENCE
 
       t = (epoch - EPOCH_OF_REFERENCE) / Epoch::DAYS_PER_JULIAN_CENTURY
 
-      new(
-        Angle.as_degrees(
-          obliquity_of_reference.degrees - (
-            46.815 * t -
-            0.0006 * t * t +
-            0.00181 * t * t * t
-          ) / 3600
-        )
+      Angle.as_degrees(
+        obliquity_of_reference.degrees - (
+          46.815 * t -
+          0.0006 * t * t +
+          0.00181 * t * t * t
+        ) / 3600
       )
     end
 
     def self.obliquity_of_reference
       Angle.as_dms(23, 26, 21.45)
     end
-
-    def value
-      @obliquity
-    end
   end
 end

lib/astronoby/true_obliquity.rb

@@ -2,19 +2,11 @@
 
 module Astronoby
   class TrueObliquity
-    def initialize(obliquity)
-      @obliquity = obliquity
-    end
-
     def self.for_epoch(epoch)
       mean_obliquity = MeanObliquity.for_epoch(epoch)
       nutation = Nutation.for_obliquity_of_the_ecliptic(epoch: epoch)
 
-      new(mean_obliquity.value + nutation)
-    end
-
-    def value
-      @obliquity
+      mean_obliquity + nutation
     end
   end
 end

spec/astronoby/mean_obliquity_spec.rb

@@ -3,19 +3,19 @@
 RSpec.describe Astronoby::MeanObliquity do
   describe "::for_epoch" do
     it "returns an angle" do
-      obliquity = described_class.for_epoch(Astronoby::Epoch::J2000).value
+      obliquity = described_class.for_epoch(Astronoby::Epoch::J2000)
 
       expect(obliquity).to be_kind_of(Astronoby::Angle)
     end
 
     it "returns the obliquity angle for standard epoch" do
-      obliquity = described_class.for_epoch(Astronoby::Epoch::J2000).value
+      obliquity = described_class.for_epoch(Astronoby::Epoch::J2000)
 
       expect(obliquity.degrees.to_f).to eq(23.439291666666666)
     end
 
     it "returns the obliquity angle for epoch 1950" do
-      obliquity = described_class.for_epoch(Astronoby::Epoch::J1950).value
+      obliquity = described_class.for_epoch(Astronoby::Epoch::J1950)
 
       expect(obliquity.degrees.to_f).to eq 23.445793854513887
     end
@@ -28,7 +28,7 @@
     context "with real life arguments (book example)" do
       it "computes properly" do
         epoch = Astronoby::Epoch.from_time(Time.utc(2009, 7, 6, 0, 0, 0))
-        obliquity = described_class.for_epoch(epoch).value
+        obliquity = described_class.for_epoch(epoch)
 
         expect(obliquity.str(:dms)).to eq "+23° 26′ 16.9979″"
       end
@@ -42,7 +42,7 @@
     context "with real life arguments (book example)" do
       it "computes properly" do
         epoch = Astronoby::Epoch.from_time(Time.utc(1987, 4, 10, 0, 0, 0))
-        obliquity = described_class.for_epoch(epoch).value
+        obliquity = described_class.for_epoch(epoch)
 
         expect(obliquity.str(:dms)).to eq "+23° 26′ 27.4093″"
       end

spec/astronoby/true_obliquity_spec.rb

@@ -3,7 +3,7 @@
 RSpec.describe Astronoby::TrueObliquity do
   describe "::for_epoch" do
     it "returns an angle" do
-      obliquity = described_class.for_epoch(Astronoby::Epoch::J2000).value
+      obliquity = described_class.for_epoch(Astronoby::Epoch::J2000)
 
       expect(obliquity).to be_kind_of(Astronoby::Angle)
     end
@@ -16,7 +16,7 @@
     context "with real life arguments (book example)" do
       it "computes properly" do
         epoch = Astronoby::Epoch.from_time(Time.utc(1987, 4, 10, 0, 0, 0))
-        obliquity = described_class.for_epoch(epoch).value
+        obliquity = described_class.for_epoch(epoch)
 
         expect(obliquity.str(:dms)).to eq "+23° 26′ 36.8401″"
       end