feat: Added getPlanetaryHeliocentricEclipticLatitude() to planets module in @observerly/astrometry.

src/planets.ts

@@ -10,7 +10,7 @@ import { J2000 } from './constants'
 
 import { getJulianDate } from './epoch'
 
-import { convertDegreesToRadians as radians } from './utilities'
+import { convertDegreesToRadians as radians, convertRadiansToDegrees as degrees } from './utilities'
 
 /*****************************************************************************************************************/
 
@@ -333,3 +333,25 @@ export const getPlanetaryHeliocentricEclipticLongitude = (
 }
 
 /*****************************************************************************************************************/
+
+/**
+ *
+ * getPlanetaryHeliocentricEclipticLatitude()
+ *
+ * @param date - The date to calculate the Sun's mean anomaly for.
+ * @param planet - The planet to calculate the mean anomaly for.
+ * @returns a planet's heliocentric ecliptic latitude at a given datetime
+ *
+ */
+export const getPlanetaryHeliocentricEclipticLatitude = (
+  datetime: Date,
+  planet: Planet
+): number => {
+  const L = getPlanetaryHeliocentricEclipticLongitude(datetime, planet)
+
+  const Ω = planet.Ω || 0
+
+  return degrees(Math.asin(Math.sin(radians(L - Ω)) * Math.sin(radians(planet.i)))) % 360
+}
+
+/*****************************************************************************************************************/

tests/planets.spec.ts

@@ -13,6 +13,7 @@ import {
   getPlanetaryMeanAnomaly,
   getPlanetaryTrueAnomaly,
   getPlanetaryHeliocentricEclipticLongitude,
+  getPlanetaryHeliocentricEclipticLatitude,
   planets
 } from '../src'
 
@@ -86,3 +87,18 @@ describe('getPlanetaryHeliocentricEclipticLongitude', () => {
 })
 
 /*****************************************************************************************************************/
+
+describe('getPlanetaryHeliocentricEclipticLatitude', () => {
+  it('should be defined', () => {
+    expect(getPlanetaryHeliocentricEclipticLatitude).toBeDefined()
+  })
+
+  it('should return the correct value for Venus at the datetime prescribed', () => {
+    const venus = planets.find(planet => planet.name === 'Venus')
+    expect(venus).toBeDefined()
+    const Λ = getPlanetaryHeliocentricEclipticLatitude(new Date('2016-01-04T03:00:00+00:00'), venus)
+    expect(Λ).toBeCloseTo(3.119613)
+  })
+})
+
+/*****************************************************************************************************************/