calculate Moon's ecliptic longitude

index.js

var date = new Date();

function normalize(v) {
    v = v - Math.floor(v);
    if (v < 0) {
      v = v + 1;
    }
    return v;
  }


function moonCoords(d) { // geocentric ecliptic coordinates of the moon
    var age, // Moon's age
      distance, // Moon's distance in earth radii
      latitude, // Moon's ecliptic latitude
      longitude, // Moon's ecliptic longitude
      phase, // Moon's phase
      trajectory, // Moon's trajectory
      zodiac; // Moon's zodiac sign 

    var yy, mm, k1, k2, k3, jd;
    var ip, dp, np, rp;

    var year = date.getFullYear();
    var month = date.getMonth()+1;
    var day = date.getDate();


    yy = year - Math.floor((12 - month) / 10);
    mm = month + 9;
    if (mm >= 12) {
      mm = mm - 12;
    }

    k1 = Math.floor(365.25 * (yy + 4712));
    k2 = Math.floor(30.6 * mm + 0.5);
    k3 = Math.floor(Math.floor((yy / 100) + 49) * 0.75) - 38;

    jd = k1 + k2 + day + 59;  // for dates in Julian calendar
    if (jd > 2299160) {
      jd = jd - k3;      // for Gregorian calendar
    }

    //calculate moon's age in days
    ip = normalize((jd - 2451550.1) / 29.530588853);

    ip = ip * 2 * Math.PI;  //Convert phase to radians

    // Calculate moon's distance
    dp = 2 * Math.PI * normalize((jd - 2451562.2) / 27.55454988);
    distance = 60.4 - 3.3 * Math.cos(dp) - 0.6 * Math.cos(2 * ip - dp) - 0.5 * Math.cos(2 * ip);

    // Calculate moon's ecliptic latitude
    np = 2 * Math.PI * normalize((jd - 2451565.2) / 27.212220817);
    latitude = 5.1 * Math.sin(np);

    // Calculate moon's ecliptic longitude
    rp = normalize((jd - 2451555.8) / 27.321582241);
    longitude = 360 * rp + 6.3 * Math.sin(dp) + 1.3 * Math.sin(2 * ip - dp) + 0.7 * Math.sin(2 * ip);
    return longitude;
}