Merge pull request #106 from observerly/feature/night/getNight

feat: Added getNight() to night module in @observerly/astrometry.

src/night.ts

@@ -88,3 +88,46 @@ export const getSolarTransit = (
 }
 
 /*****************************************************************************************************************/
+
+/**
+ *
+ * getNight()
+ *
+ * Calculates the start and end of the next night for the observer at the given date.
+ *
+ * @param date - The date to calculate the extent of the next night for.
+ * @param observer - The geographic coordinates of the observer.
+ * @param horizon - The horizon altitude to use for the calculation.
+ * @param temperature - The temperature to use for the calculation.
+ * @param pressure - The pressure to use for the calculation.
+ * @returns The start and end of the next night for the observer.
+ *
+ */
+export const getNight = (
+  datetime: Date,
+  observer: GeographicCoordinate,
+  horizon: number = -12,
+  temperature: number = 288.15,
+  pressure: number = 101325
+): {
+  start: Date | null
+  end: Date | null
+} => {
+  const { sunset } = getSolarTransit(datetime, observer, horizon, temperature, pressure)
+
+  const { sunrise } = getSolarTransit(
+    new Date(datetime.getTime() + 60000 * 60 * 24),
+    observer,
+    horizon,
+    temperature,
+    pressure
+  )
+
+  // The observer could be in perpetual daylight or perpetual night, e.g., the North Pole or South Pole:
+  return {
+    start: sunset,
+    end: sunrise
+  }
+}
+
+/*****************************************************************************************************************/

tests/night.spec.ts

@@ -10,7 +10,7 @@ import { describe, expect, it } from 'vitest'
 
 /*****************************************************************************************************************/
 
-import { getSolarTransit } from '../src'
+import { getSolarTransit, getNight } from '../src'
 
 /*****************************************************************************************************************/
 
@@ -67,3 +67,28 @@ describe('getSolarTransit', () => {
 })
 
 /*****************************************************************************************************************/
+
+describe('getNight', () => {
+  it('should be defined', () => {
+    expect(getNight).toBeDefined()
+  })
+
+  it('should return the correct night for the observer at a horizon of 0 degrees', () => {
+    const { start, end } = getNight(
+      datetime,
+      {
+        latitude,
+        longitude
+      },
+      0
+    )
+
+    expect(start).toBeInstanceOf(Date)
+    expect(end).toBeInstanceOf(Date)
+
+    expect(start?.toISOString()).toBe('2021-05-14T19:56:00.000Z')
+    expect(end?.toISOString()).toBe('2021-05-15T04:45:00.000Z')
+  })
+})
+
+/*****************************************************************************************************************/