var BLOCKOUT = 3;       // blockout angle around zenith

var alt = 0; // altitude, degrees

var az  = 0; // azimuthal angle, degrees

var t = 0;

var dec_slider;

var speed_slider;

var decdiv;

var speeddiv;

​

function setup() {

  createCanvas(400, 400,WEBGL);

  decdiv = createDiv("Dec")

  dec_slider = createSlider(0.001,180,90-(phi-3),0.1);

  speeddiv = createDiv("Speed")

  speed_slider = createSlider(0,5,2,0.01);

}

​

function draw() {

  var de = dec_slider.value()+90; // declination, degrees

  var hamin = -acos((0.5-sin(de)*sin(phi))/(cos(de)*cos(phi)))

  var hamax = -hamin;

  var ha; // hour angle, degrees

  //if (t > hamax)

  //  t = hamin;

  t += speed_slider.value();

  ha = t;

  alt = asin(sin(de)*sin(phi)+cos(de)*cos(ha)*cos(phi));

  az  = atan2(sin(ha),(cos(ha)*sin(phi)-tan(de)*cos(phi)));

  angleMode(DEGREES);

  camera(0, -100, 200)

  background(0,0,100);

  noStroke();

  push();

  rotateX(90);

  fill(100);

  plane(1000,1000);

  pop();

  push();

  translate(-50,-10,110);

  noStroke();

  fill(200);

  rotateZ(90);

  cylinder(2,20);

  translate(0,10,0)

  cone(5,10);

  pop();

  push();

  var telheight = 20;

  var scopelen = 30;

  rotateY(az);

  translate(0,-telheight/2,0);

  stroke(100,0,0);

  fill(255,0,0);

  box(30,telheight,30);

  rotateZ(-alt);

  translate(scopelen/2,0,0);

  box(scopelen,10,10);

  noStroke();

  fill(0,255,0);

  translate(70,0,0);

  sphere(4);  

  pop();

  decdiv.html("Dec: "+(de-90).toFixed(2))

  speeddiv.html("Speed up: "+speed_slider.value().toFixed(2))

}