Merge pull request #397 from observerly/feature/refraction/getRefraction

feat: add getRefraction() to refraction module in @observerly/astrometry

Author: michealroberts

src/refraction.ts

@@ -14,26 +14,28 @@ import { convertDegreesToRadians as radians } from './utilities'
 
 /**
  *
- * getCorrectionToHorizontalForRefraction()
+ * getRefraction()
  *
- * The correct to the HorizontalCoordinate for refraction is an adjustment to the observed
- * HorizontalCoordinate based on pressure and temperature effects.
+ * The refraction correction to the observed object is an adjustment to the observed object
+ * based on pressure and temperature effects.
+ *
+ * N.B. There is no correction for the azimuthal angle.
  *
  * @param target - The horizontal coordinate of the observed object.
  * @param temperature - The temperature in Kelvin.
  * @param pressure - The pressure in Pascals.
- * @returns The horizontal coordinate of the observed object corrected for atmospheric refraction.
+ * @returns The refraction correction to the observed object (in degrees).
  *
  */
-export const getCorrectionToHorizontalForRefraction = (
+export const getRefraction = (
   target: HorizontalCoordinate,
   temperature: number = 283.15,
   pressure: number = 101325
-): HorizontalCoordinate => {
-  const { alt, az } = target
+): number => {
+  const { alt } = target
 
   if (alt < 0) {
-    return target
+    return Number.POSITIVE_INFINITY
   }
 
   // The pressure, in Pascals:
@@ -45,6 +47,38 @@ export const getCorrectionToHorizontalForRefraction = (
   // Get the atmospheric refraction in degrees, corrected for temperature and pressure:
   const R = (1.02 / Math.tan(radians(alt + 10.3 / (alt + 5.11))) / 60) * (P / 101325) * (283.15 / T)
 
+  return R
+}
+
+/*****************************************************************************************************************/
+
+/**
+ *
+ * getCorrectionToHorizontalForRefraction()
+ *
+ * The correction to the HorizontalCoordinate for refraction is an adjustment to the observed
+ * HorizontalCoordinate based on pressure and temperature effects.
+ *
+ * @param target - The horizontal coordinate of the observed object.
+ * @param temperature - The temperature in Kelvin.
+ * @param pressure - The pressure in Pascals.
+ * @returns The horizontal coordinate of the observed object corrected for atmospheric refraction.
+ *
+ */
+export const getCorrectionToHorizontalForRefraction = (
+  target: HorizontalCoordinate,
+  temperature: number = 283.15,
+  pressure: number = 101325
+): HorizontalCoordinate => {
+  const { alt, az } = target
+
+  if (alt < 0) {
+    return target
+  }
+
+  // Get the atmospheric refraction in degrees, corrected for temperature and pressure:
+  const R = getRefraction(target, temperature, pressure)
+
   return {
     alt: alt + R,
     az: az

tests/refraction.spec.ts

@@ -13,7 +13,8 @@ import { describe, expect, it } from 'vitest'
 import {
   type EquatorialCoordinate,
   convertEquatorialToHorizontal,
-  getCorrectionToHorizontalForRefraction
+  getCorrectionToHorizontalForRefraction,
+  getRefraction
 } from '../src'
 
 /*****************************************************************************************************************/
@@ -33,6 +34,31 @@ const betelgeuse: EquatorialCoordinate = { ra: 88.7929583, dec: 7.4070639 }
 
 /*****************************************************************************************************************/
 
+describe('getRefraction', () => {
+  it('should be defined', () => {
+    expect(getRefraction).toBeDefined()
+  })
+
+  it('should return the refraction correction to the observed object', () => {
+    const target = convertEquatorialToHorizontal(
+      datetime,
+      {
+        latitude,
+        longitude
+      },
+      betelgeuse
+    )
+
+    expect(target.az).toBe(134.44877920325155)
+    expect(target.alt).toBe(72.78539444063765)
+
+    const R = getRefraction(target, 283.15, 101325)
+    expect(R).toBe(0.005224159687428409)
+  })
+})
+
+/*****************************************************************************************************************/
+
 describe('getCorrectionToHorizontalForRefractione', () => {
   it('should be defined', () => {
     expect(getCorrectionToHorizontalForRefraction).toBeDefined()