Minimal Julian Clock

snippet.html

<script type="text/javascript">
  function currentJulianDay() {
    var epoch = 2440587.500000; // Jan. 1, 1970 00:00:00 UTC, Julian
    var day = (new Date()).getTime() / 86400000 + epoch;
    return day.toFixed(5);
  }
  
  function writeTime() {
    document.getElementById("julian-clock").innerHTML = currentJulianDay();
  }
  
  setInterval(writeTime, 1000);
</script>
<div id="julian-clock"></div>