Dynamically created sky map using Fourmilab's Your Sky

brahe.html

<script>
  var toUrlParam = function(date) {
    return date.toISOString().split("T")[0].replaceAll("-", "%2F");
  }
  
  // https://stackoverflow.com/questions/563406/add-days-to-javascript-date
  Date.prototype.addDays = function(days) {
    var date = new Date(this.valueOf());
    date.setDate(date.getDate() + days);
    return date;
  }
  
  var date = new Date("1576-11-01");
  var imgTag;
  
  var updateImage = function() {
    date = date.addDays(1);
    imgTag.src = `https://www.fourmilab.ch/cgi-bin/Yoursky?date=1&utc=${toUrlParam(date)}+12%3A42%3A40&jd=2450851.02963&lat=56.0881&ns=North&lon=13.2322&ew=East&coords=on&moonp=on&deepm=2.5&limag=5.5&starnm=2.0&starbm=2.5&imgsize=640&dynimg=y&fontscale=0.75&scheme=1&elements=`;
  }
  
  document.addEventListener("DOMContentLoaded", function() {
    imgTag = document.createElement("img")
    updateImage()
    document.querySelector("body").appendChild(imgTag);
    setInterval(updateImage, 150);
  })
</script>

I made the GIF that appears on https://observablehq.com/d/1838567c160ca917 by opening the above html page in a browser and taking a short screencap.

Neat!