Add Angle#-

lib/astronoby/aberration.rb

@@ -22,13 +22,13 @@ def apply
       delta_longitude = Astronoby::Angle.as_degrees(
         -20.5 *
         Math.cos(
-          @sun_longitude.radians - @coordinates.longitude.radians
+          (@sun_longitude - @coordinates.longitude).radians
         ) / Math.cos(@coordinates.latitude.radians) / 3600
       )
 
       delta_latitude = Astronoby::Angle.as_degrees(
         -20.5 *
-        Math.sin(@sun_longitude.radians - @coordinates.longitude.radians) *
+        Math.sin((@sun_longitude - @coordinates.longitude).radians) *
         Math.sin(@coordinates.latitude.radians) / 3600
       )
 

lib/astronoby/angle.rb

@@ -69,6 +69,10 @@ def +(other)
       self.class.as_radians(radians + other.radians)
     end
 
+    def -(other)
+      self.class.as_radians(@radians - other.radians)
+    end
+
     def str(format)
       case format
       when :dms then to_dms(degrees).format

lib/astronoby/bodies/sun.rb

@@ -33,7 +33,7 @@ def horizontal_coordinates(latitude:, longitude:)
 
     def mean_anomaly
       Angle.as_degrees(
-        (longitude_at_base_epoch.degrees - longitude_at_perigee.degrees) % 360
+        (longitude_at_base_epoch - longitude_at_perigee).degrees % 360
       )
     end
 

spec/astronoby/angle_spec.rb

@@ -104,6 +104,17 @@
     end
   end
 
+  describe "#-" do
+    it "returns a new angle with a value of the two angles substracted" do
+      angle_1 = described_class.as_radians(described_class::PI)
+      angle_2 = described_class.as_degrees(45)
+
+      new_angle = angle_1 - angle_2
+
+      expect(new_angle.degrees).to eq 135
+    end
+  end
+
   describe "#str" do
     it "returns a String" do
       angle = described_class.as_degrees(180)