Merge pull request #27 from observerly/feature/coordinates/ConvertEcl…

…ipticToEquatorial

feat: add ConvertEclipticToEquatorialCoordinate(datetime time.Time) to coordinates module in @observerly/sidera.

pkg/coordinates/coordinates.go

@@ -0,0 +1,59 @@
+/*****************************************************************************************************************/
+
+//	@author		Michael Roberts <michael@observerly.com>
+//	@package	@observerly/sidera
+//	@license	Copyright © 2021-2024 observerly
+
+/*****************************************************************************************************************/
+
+package coordinates
+
+import (
+	"math"
+	"time"
+
+	"github.com/observerly/sidera/pkg/astrometry"
+	"github.com/observerly/sidera/pkg/common"
+)
+
+/*****************************************************************************************************************/
+
+/*
+converts ecliptic to equatorial coordinates
+
+The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of
+celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an
+origin at the center of Earth, a fundamental plane consisting of the projection of Earth's equator onto
+the celestial sphere (forming the celestial equator), a primary direction towards the vernal equinox,
+and a right-handed convention.
+
+The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental
+plane. The ecliptic is the plane of Earth's orbit around the Sun, and is defined by the projection of the
+Earth's orbit onto the celestial sphere. The ecliptic coordinate system is widely used in astronomy to
+specify the positions of celestial objects in the sky.
+*/
+func ConvertEclipticToEquatorialCoordinate(
+	datetime time.Time,
+	target common.EclipticCoordinate,
+) (equatorial common.EquatorialCoordinate) {
+	ε := common.Radians(astrometry.GetObliquityOfTheEcliptic(datetime))
+
+	λ := common.Radians(target.Longitude)
+
+	β := common.Radians(target.Latitude)
+
+	α := common.Degrees(math.Atan2(math.Sin(λ)*math.Cos(ε)-math.Tan(β)*math.Sin(ε), math.Cos(λ)))
+
+	δ := common.Degrees(math.Asin(math.Sin(β)*math.Cos(ε) + math.Cos(β)*math.Sin(ε)*math.Sin(λ)))
+
+	if α < 0 {
+		α += 360
+	}
+
+	return common.EquatorialCoordinate{
+		RightAscension: math.Mod(α, 360),
+		Declination:    δ,
+	}
+}
+
+/*****************************************************************************************************************/

pkg/coordinates/coordinates_test.go

@@ -0,0 +1,38 @@
+/*****************************************************************************************************************/
+
+//	@author		Michael Roberts <michael@observerly.com>
+//	@package	@observerly/sidera
+//	@license	Copyright © 2021-2024 observerly
+
+/*****************************************************************************************************************/
+
+package coordinates
+
+import (
+	"testing"
+	"time"
+
+	"github.com/observerly/sidera/pkg/common"
+	"github.com/stretchr/testify/assert"
+)
+
+/*****************************************************************************************************************/
+
+// We define a datetime as some arbitrary date and time for testing purposes:
+var datetime time.Time = time.Date(2021, 5, 14, 0, 0, 0, 0, time.UTC)
+
+/*****************************************************************************************************************/
+
+func TestConvertEclipticToEquatorialCoordinate(t *testing.T) {
+	venus := common.EclipticCoordinate{
+		Longitude: 245.79403406596947,
+		Latitude:  1.8937944394473665,
+	}
+
+	eq := ConvertEclipticToEquatorialCoordinate(datetime, venus)
+
+	assert.Equal(t, eq.RightAscension, 244.24810079259953)
+	assert.Equal(t, eq.Declination, -19.405047833538664)
+}
+
+/*****************************************************************************************************************/