Merge pull request #101 from observerly/feature/moon/getLunarPhase

src/moon.ts

@@ -651,3 +651,51 @@ export const getLunarIllumination = (datetime: Date): number => {
 }
 
 /*****************************************************************************************************************/
+
+/**
+ *
+ * getLunarPhase()
+ *
+ * The phase of the Moon is the shape of the Moon's illuminated portion
+ * as seen from the Earth.
+ *
+ * @param date - The date to calculate the Moon's phase for.
+ * @returns The phase of the Moon.
+ *
+ */
+export const getLunarPhase = (datetime: Date): Phase => {
+  // Get the age of the Moon:
+  const { age } = getLunarAge(datetime)
+
+  if (age >= 0 && age < 3.7) {
+    return Phases.WaningCrescent
+  }
+
+  if (age >= 3.7 && age < 7.4) {
+    return Phases.WaxingCrescent
+  }
+
+  if (age >= 7.4 && age < 11.1) {
+    return Phases.FirstQuarter
+  }
+
+  if (age >= 11.1 && age < 14.6) {
+    return Phases.WaxingGibbous
+  }
+
+  if (age >= 14.6 && age < 15.0) {
+    return Phases.Full
+  }
+
+  if (age >= 15.0 && age < 22.1) {
+    return Phases.WaningGibbous
+  }
+
+  if (age >= 22.1 && age < 25.8) {
+    return Phases.LastQuarter
+  }
+
+  return Phases.New
+}
+
+/*****************************************************************************************************************/

tests/moon.spec.ts

@@ -30,7 +30,8 @@ import {
   getLunarDistance,
   getLunarAge,
   getLunarPhaseAngle,
-  getLunarIllumination
+  getLunarIllumination,
+  getLunarPhase
 } from '../src'
 
 /*****************************************************************************************************************/
@@ -310,3 +311,35 @@ describe('getLunarIllumination', () => {
 })
 
 /*****************************************************************************************************************/
+
+describe('getLunarPhase', () => {
+  it('should be defined', () => {
+    expect(getLunarPhase).toBeDefined()
+  })
+
+  it('should return the correct Lunar phase for the given date as Waxing Gibbous', () => {
+    const datetime = new Date('2015-01-02T02:00:00.000+00:00')
+    const phase = getLunarPhase(datetime)
+    expect(phase).toBe('Waxing Gibbous')
+  })
+
+  it('should return the correct Lunar phase for the given date as Full Moon', () => {
+    const datetime = new Date('2015-01-05T07:00:00.000+00:00')
+    const phase = getLunarPhase(datetime)
+    expect(phase).toBe('Full')
+  })
+
+  it('should return the correct Lunar phase for the given date as Waning Gibbous', () => {
+    const datetime = new Date('2015-01-07T23:00:00.000+00:00')
+    const phase = getLunarPhase(datetime)
+    expect(phase).toBe('Waning Gibbous')
+  })
+
+  it('should return the correct Lunar phase for the given date as Last Quarter', () => {
+    const datetime = new Date('2015-02-12T17:00:00.000+00:00')
+    const phase = getLunarPhase(datetime)
+    expect(phase).toBe('Last Quarter')
+  })
+})
+
+/*****************************************************************************************************************/