code: function jd0(year, month, day) {
    let y  = year;
    let m = month;
    if (m < 3) {
      m += 12;
      y -= 1
    };
    const a = Math.floor(y/100);
    const b = 2-a+Math.floor(a/4);
    const j = Math.floor(365.25*(y+4716))+Math.floor(30.6001*(m+1))+day+b-1524.5;
    return j;
  }
docs: The Julian date at 0 hours UT at Greenwich