test.html

<script>
var LONGITUDE = 0.0;
	
function decimalhours(now) {
  return (((now.getSeconds() / 60) + now.getUTCMinutes()) / 60) + now.getUTCHours(); 
}

function juliandate(now) {
  var y = now.getUTCFullYear();
  var m = now.getUTCMonth() + 1;
  var d = now.getUTCDate();
  if ((m == 1) || (m == 2)){
    y = y - 1;
    m = m + 12;
  }
  var A = Math.floor(y / 100);
  var B = 2 - A + Math.floor(A / 4);
  var C = Math.floor(365.25 * y);
  var D = Math.floor(30.6001 * (m + 1));
  return (B + C + D + d + 1720994.5);
}

function gst(jd, dechours) {
  console.log("JD: " + jd);
  var S = jd - 2451545;
  var T = S / 36525;
  var T0 = 6.697374558 + (2400.051336 * T) + (0.000025862 * Math.pow(T, 2));
  if (Math.sign(T0) == -1){
    T0 = (T0 + (24 * Math.abs(Math.floor(T0 / 24))));
  } else {
    T0 = (T0 - (24 * Math.abs(Math.floor(T0 / 24)))); 
  }
  T0 = T0 + (dechours * 1.002737909);
  if (T0 < 0) {T0 = T0 + 24};
  if (T0 > 24) {T0 = T0 - 24};
  var h = Math.floor(T0);
  var m1 = T0 - h;
  var m = Math.floor((T0 - h) * 60);
  var s = Math.floor((((T0 - h) * 60) - m) *  60);
  console.log("T0: " + T0);
  return T0;
}

function lst(gstime) {
  var lstime;
  var utcdiff = LONGITUDE / 15;
  lstime = gstime + utcdiff;

  lstime = (lstime + 24) % 24;

  return lstime;
}

function setPosition(position) {

	// njiov algoritam
	LONGITUDE = position.coords.longitude;
	var now = new Date();
    nowjd = juliandate(now);
    nowdechours = decimalhours(now);
	var lst1 = lst(gst(nowjd, nowdechours))
    console.log(lst1);
	
	// moj algoritam
	var now_ms = now.getTime();
	var j2000 = Date.parse("Jan 1, 2000, 12:00");
	var sidereal_days = (now_ms - j2000) / 8.616409E+7;
	var sidereal_time = ((sidereal_days % 1) * 24 + LONGITUDE / 15 - 6.30677 + 24) % 24;
	console.log(sidereal_time);
	
	console.log(lst1 - sidereal_time);
}
  navigator.geolocation.getCurrentPosition(setPosition);
</script>