astronomia/es/stellar.js

/**
 * @copyright 2013 Sonia Keys
 * @copyright 2016 commenthol
 * @license MIT
 * @module stellar
 */
/**
 * Stellar: Chapter 56, Stellar Magnitudes.
 */

/**
 * Sum returns the combined apparent magnitude of two stars.
 */
export function sum(m1, m2) {
  // (m1, m2 float64)  float64
  var x = 0.4 * (m2 - m1);
  return m2 - 2.5 * Math.log10(Math.pow(10, x) + 1);
}

/**
 * SumN returns the combined apparent magnitude of a number of stars.
 */
export function sumN(m) {
  // (m ...float64)  float64
  var s = 0;
  for (var _iterator = m, _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
    var _ref;

    if (_isArray) {
      if (_i >= _iterator.length) break;
      _ref = _iterator[_i++];
    } else {
      _i = _iterator.next();
      if (_i.done) break;
      _ref = _i.value;
    }

    var mi = _ref;

    s += Math.pow(10, -0.4 * mi);
  }
  return -2.5 * Math.log10(s);
}

/**
 * Ratio returns the brightness ratio of two stars.
 *
 * Arguments m1, m2 are apparent magnitudes.
 */
export function ratio(m1, m2) {
  // (m1, m2 float64)  float64
  var x = 0.4 * (m2 - m1);
  return Math.pow(10, x);
}

/**
 * Difference returns the difference in apparent magnitude of two stars
 * given their brightness ratio.
 */
export function difference(ratio) {
  // (ratio float64)  float64
  return 2.5 * Math.log10(ratio);
}

/**
 * AbsoluteByParallax returns absolute magnitude given annual parallax.
 *
 * Argument m is apparent magnitude, π is annual parallax in arc seconds.
 */
export function absoluteByParallax(m, π) {
  // (m, π float64)  float64
  return m + 5 + 5 * Math.log10(π);
}

/**
 * AbsoluteByDistance returns absolute magnitude given distance.
 *
 * Argument m is apparent magnitude, d is distance in parsecs.
 */
export function absoluteByDistance(m, d) {
  // (m, d float64)  float64
  return m + 5 - 5 * Math.log10(d);
}

export default {
  sum: sum,
  sumN: sumN,
  ratio: ratio,
  difference: difference,
  absoluteByParallax: absoluteByParallax,
  absoluteByDistance: absoluteByDistance
};