134 lines
3.6 KiB
JavaScript
134 lines
3.6 KiB
JavaScript
'use strict';
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Object.defineProperty(exports, '__esModule', { value: true });
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var base = require('./base.cjs');
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var nutation = require('./nutation.cjs');
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/**
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* @copyright 2013 Sonia Keys
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* @copyright 2016 commenthol
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* @license MIT
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* @module sidereal
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*/
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/**
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* JDToCFrac returns values for use in computing sidereal time at Greenwich.
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*
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* Cen is centuries from J2000 of the JD at 0h UT of argument jd. This is
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* the value to use for evaluating the IAU sidereal time polynomial.
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* DayFrac is the fraction of jd after 0h UT. It is used to compute the
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* final value of sidereal time.
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*
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* @param {number} jd - Julian Days
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* @return {number[]} [century, fraction] century and fraction of jd after 0h UT
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*/
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function JDToCFrac (jd) {
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const [j0, f] = base["default"].modf(jd + 0.5);
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return [base["default"].J2000Century(j0 - 0.5), f] // (cen, dayFrac /* float */)
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}
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/**
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* iau82 is a polynomial giving mean sidereal time at Greenwich at 0h UT.
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*
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* The polynomial is in centuries from J2000.0, as given by JDToCFrac.
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* Coefficients are those adopted in 1982 by the International Astronomical
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* Union and are given in (12.2) p. 87.
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*/
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const iau82 = [24110.54841, 8640184.812866, 0.093104, -0.0000062];
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/**
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* Mean returns mean sidereal time at Greenwich for a given JD.
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*
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* Computation is by IAU 1982 coefficients. The result is in seconds of
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* time and is in the range [0,86400).
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*
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* @param {number} jd - Julian Days
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* @return {number}
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*/
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function mean (jd) {
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return base["default"].pmod(_mean(jd), 86400)
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}
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/**
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* @private
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*/
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function _mean (jd) {
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const [s, f] = _mean0UT(jd);
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return s + f * 1.00273790935 * 86400
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}
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/**
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* Mean0UT returns mean sidereal time at Greenwich at 0h UT on the given JD.
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*
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* The result is in seconds of time and is in the range [0,86400).
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*
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* @param {number} jd - Julian Days
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* @return {number}
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*/
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function mean0UT (jd /* float */) {
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const [s, _] = _mean0UT(jd); // eslint-disable-line
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return base["default"].pmod(s, 86400)
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}
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/**
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* @private
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*/
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function _mean0UT (jd /* float */) {
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const [cen, f] = JDToCFrac(jd);
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// (12.2) p. 87
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return [base["default"].horner(cen, ...iau82), f] // (sidereal, dayFrac /* float */)
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}
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/**
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* Apparent returns apparent sidereal time at Greenwich for the given JD.
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*
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* Apparent is mean plus the nutation in right ascension.
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*
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* The result is in seconds of time and is in the range [0,86400).
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*
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* @param {number} jd - Julian Days
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* @return {number}
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*/
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function apparent (jd) {
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const s = _mean(jd); // seconds of time
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const n = nutation["default"].nutationInRA(jd); // angle (radians) of RA
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const ns = n * 3600 * 180 / Math.PI / 15; // convert RA to time in seconds
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return base["default"].pmod(s + ns, 86400)
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}
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/**
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* Apparent0UT returns apparent sidereal time at Greenwich at 0h UT
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* on the given JD.
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*
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* The result is in seconds of time and is in the range [0,86400).
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*
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* @param {number} jd - Julian Days
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* @return {number}
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*/
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function apparent0UT (jd) {
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const [j0, f] = base["default"].modf(jd + 0.5);
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const cen = (j0 - 0.5 - base["default"].J2000) / 36525;
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const s = base["default"].horner(cen, ...iau82) + f * 1.00273790935 * 86400;
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const n = nutation["default"].nutationInRA(j0); // angle (radians) of RA
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const ns = n * 3600 * 180 / Math.PI / 15; // convert RA to time in seconds
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return base["default"].pmod(s + ns, 86400)
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}
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var sidereal = {
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JDToCFrac,
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iau82,
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mean,
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mean0UT,
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apparent,
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apparent0UT
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};
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exports.JDToCFrac = JDToCFrac;
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exports.apparent = apparent;
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exports.apparent0UT = apparent0UT;
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exports["default"] = sidereal;
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exports.iau82 = iau82;
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exports.mean = mean;
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exports.mean0UT = mean0UT;
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