Merge pull request #107 from observerly/feature/night/isNight

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

src/night.ts

@@ -131,3 +131,32 @@ export const getNight = (
 }
 
 /*****************************************************************************************************************/
+
+export const isNight = (
+  datetime: Date,
+  observer: GeographicCoordinate,
+  horizon: number = -12,
+  temperature: number = 288.15,
+  pressure: number = 101325
+) => {
+  const when = new Date(
+    datetime.getFullYear(),
+    datetime.getMonth(),
+    datetime.getDate(),
+    datetime.getHours(),
+    datetime.getMinutes(),
+    datetime.getSeconds(),
+    datetime.getMilliseconds()
+  )
+
+  const { sunrise, sunset } = getSolarTransit(datetime, observer, horizon, temperature, pressure)
+
+  if (sunrise === null || sunset === null) {
+    return false
+  }
+
+  // If the datetime is before sunrise or after sunset, it is night:
+  return when.getTime() <= sunrise.getTime() || when.getTime() >= sunset.getTime()
+}
+
+/*****************************************************************************************************************/

tests/night.spec.ts

@@ -10,7 +10,7 @@ import { describe, expect, it } from 'vitest'
 
 /*****************************************************************************************************************/
 
-import { getSolarTransit, getNight } from '../src'
+import { getSolarTransit, getNight, isNight } from '../src'
 
 /*****************************************************************************************************************/
 
@@ -92,3 +92,76 @@ describe('getNight', () => {
 })
 
 /*****************************************************************************************************************/
+
+describe('isNight', () => {
+  it('should be defined', () => {
+    expect(isNight).toBeDefined()
+  })
+
+  it('should return true for the observer at a horizon of 0 degrees', () => {
+    expect(
+      isNight(
+        datetime,
+        {
+          latitude,
+          longitude
+        },
+        0
+      )
+    ).toBe(true)
+  })
+
+  it('should return true for the observer at a horizon of 0 degrees at midnight on the current day', () => {
+    expect(
+      isNight(
+        datetime,
+        {
+          latitude,
+          longitude
+        },
+        0
+      )
+    ).toBe(true)
+  })
+
+  it('should return false for the observer at a horizon of 0 degrees after sunrise at ~7am on the current day', () => {
+    expect(
+      isNight(
+        new Date('2021-05-14T06:55:00.000+00:00'),
+        {
+          latitude,
+          longitude
+        },
+        0
+      )
+    ).toBe(false)
+  })
+
+  it('should return false for the observer at a horizon of 0 degrees after sunrise at "noon" on the current day', () => {
+    expect(
+      isNight(
+        new Date('2021-05-14T12:00:00.000+00:00'),
+        {
+          latitude,
+          longitude
+        },
+        0
+      )
+    ).toBe(false)
+  })
+
+  it('should return true for the observer at a horizon of 0 degrees after sunset at 9pm on the current day', () => {
+    expect(
+      isNight(
+        new Date('2021-05-14T21:00:00.000+00:00'),
+        {
+          latitude,
+          longitude
+        },
+        0
+      )
+    ).toBe(true)
+  })
+})
+
+/*****************************************************************************************************************/