astronomia/src/node.js

An astronomical library

/**
 * @copyright 2013 Sonia Keys
 * @copyright 2016 commenthol
 * @license MIT
 * @module node
 */
/**
 * Node: Chapter 39, Passages through the Nodes.
 */

import base from './base.js'

/**
 * EllipticAscending computes time and distance of passage through the ascending node of a body in an elliptical orbit.
 *
 * Argument axis is semimajor axis in AU, ecc is eccentricity, argP is argument
 * of perihelion in radians, timeP is time of perihelion as a jd.
 *
 * Result is jde of the event and distance from the sun in AU.
 */
export function ellipticAscending (axis, ecc, argP, timeP) { // (axis, ecc, argP, timeP float64)  (jde, r float64)
  return el(-argP, axis, ecc, timeP)
}

/**
 * EllipticAscending computes time and distance of passage through the descending node of a body in an elliptical orbit.
 *
 * Argument axis is semimajor axis in AU, ecc is eccentricity, argP is argument
 * of perihelion in radians, timeP is time of perihelion as a jd.
 *
 * Result is jde of the event and distance from the sun in AU.
 */
export function ellipticDescending (axis, ecc, argP, timeP) { // (axis, ecc, argP, timeP float64)  (jde, r float64)
  return el(Math.PI - argP, axis, ecc, timeP)
}

export function el (ν, axis, ecc, timeP) { // (ν, axis, ecc, timeP float64)  (jde, r float64)
  const E = 2 * Math.atan(Math.sqrt((1 - ecc) / (1 + ecc)) * Math.tan(ν * 0.5))
  const [sE, cE] = base.sincos(E)
  const M = E - ecc * sE
  const n = base.K / axis / Math.sqrt(axis)
  const jde = timeP + M / n
  const r = axis * (1 - ecc * cE)
  return [jde, r]
}

/**
 * ParabolicAscending computes time and distance of passage through the ascending node of a body in a parabolic orbit.
 *
 * Argument q is perihelion distance in AU, argP is argument of perihelion
 * in radians, timeP is time of perihelion as a jd.
 *
 * Result is jde of the event and distance from the sun in AU.
 */
export function parabolicAscending (q, argP, timeP) { // (q, argP, timeP float64)  (jde, r float64)
  return pa(-argP, q, timeP)
}

/**
 * ParabolicDescending computes time and distance of passage through the descending node of a body in a parabolic orbit.
 *
 * Argument q is perihelion distance in AU, argP is argument of perihelion
 * in radians, timeP is time of perihelion as a jd.
 *
 * Result is jde of the event and distance from the sun in AU.
 */
export function parabolicDescending (q, argP, timeP) { // (q, argP, timeP float64)  (jde, r float64)
  return pa(Math.PI - argP, q, timeP)
}

export function pa (ν, q, timeP) { // (ν, q, timeP float64)  (jde, r float64)
  const s = Math.tan(ν * 0.5)
  const jde = timeP + 27.403895 * s * (s * s + 3) * q * Math.sqrt(q)
  const r = q * (1 + s * s)
  return [jde, r]
}

export default {
  ellipticAscending,
  ellipticDescending,
  el,
  parabolicAscending,
  parabolicDescending,
  pa
}