Polar Clock III by mbostock

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  background: #222;
  margin: auto;
  width: 960px;
}

.field-track,
.field-arm {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
}

.field-tick {
  transition: opacity 750ms linear;
}

.field-tick:not(.field-tick--active) circle,
.field-tick:not(.field-tick--active):first-of-type text {
  fill: #222 !important;
}

.field-tick:not(.field-tick--active):first-of-type circle {
  fill: #000 !important;
}

.field-tick--disabled {
  opacity: 0;
}

.field-tick circle,
.field-tick text {
  transition: fill 250ms linear;
  transition-delay: 400ms;
}

.field-tick text {
  font: 700 14px "Helvetica Neue";
  text-anchor: middle;
}

</style>
<svg width="960" height="960"></svg>
<script src="//d3js.org/d3.v4.0.0-alpha.28.min.js"></script>
<script>

var svg = d3.select("svg"),
    width = +svg.attr("width"),
    height = +svg.attr("height"),
    radius = Math.min(width, height) / 1.9,
    armRadius = radius / 22,
    dotRadius = armRadius - 6;

var duration = 750,
    now = new Date(Date.now() + 2 * duration);

var pi = Math.PI,
    tau = pi * 2;

var fields = [
  {radius: 0.2 * radius, interval: d3.timeYear,   subinterval: d3.timeMonth,  format: d3.timeFormat("%b")},
  {radius: 0.3 * radius, interval: d3.timeMonth,  subinterval: d3.timeDay,    format: d3.timeFormat("%d")},
  {radius: 0.4 * radius, interval: d3.timeWeek,   subinterval: d3.timeDay,    format: d3.timeFormat("%a")},
  {radius: 0.6 * radius, interval: d3.timeDay,    subinterval: d3.timeHour,   format: d3.timeFormat("%H")},
  {radius: 0.7 * radius, interval: d3.timeHour,   subinterval: d3.timeMinute, format: d3.timeFormat("%M")},
  {radius: 0.8 * radius, interval: d3.timeMinute, subinterval: d3.timeSecond, format: d3.timeFormat("%S")}
];

var color = d3.scaleRainbow()
    .domain([0, tau]);

var arcArm = d3.arc()
    .startAngle(function(d) { return armRadius / d.radius; })
    .endAngle(function(d) { return -pi - armRadius / d.radius; })
    .innerRadius(function(d) { return d.radius - armRadius; })
    .outerRadius(function(d) { return d.radius + armRadius; })
    .cornerRadius(armRadius);

var field = svg.append("g")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")")
  .selectAll(".field")
    .data(fields)
  .enter().append("g")
    .attr("class", "field");

field.append("circle")
    .attr("class", "field-track")
    .attr("r", function(d) { return d.radius; });

var fieldTick = field.selectAll(".field-tick")
    .data(function(d) {
      var date = d.interval(new Date(2000, 0, 1));
      d.range = d.subinterval.range(date, d.interval.offset(date, 1));
      return d.range.map(function(t) { return {time: t, field: d}; });
    })
  .enter().append("g")
    .attr("class", "field-tick")
    .attr("transform", function(d, i) {
      var angle = i / d.field.range.length * tau - pi / 2;
      return "translate(" + Math.cos(angle) * d.field.radius + "," + Math.sin(angle) * d.field.radius + ")";
    });

fieldTick.append("circle")
    .attr("r", dotRadius - 3)
    .style("fill", function(d, i) { return color(i / d.field.range.length * tau); });

fieldTick.append("text")
    .attr("dy", "0.35em")
    .text(function(d) { return d.field.format(d.time).slice(0, 2); });

var fieldArm = field.append("path")
    .attr("class", "field-arm")
    .attr("transform", "rotate(0)")
    .attr("d", function(d) {
      return arcArm(d)
          + "M0," + (dotRadius - d.radius)
          + "a" + dotRadius + "," + dotRadius + " 0 0,1 0," + -dotRadius * 2
          + "a" + dotRadius + "," + dotRadius + " 0 0,1 0," + dotRadius * 2;
    });

(function tick() {
  var now = new Date,
      then = new Date(+now + duration),
      next = d3.timeSecond.offset(d3.timeSecond(then), 1),
      delay = next - duration - now;

  // Skip ahead a second if there’s not time for this transition.
  if (delay < duration) delay += 1000, then = next;

  fieldArm.transition()
      .duration(duration)
      .each(function(d) {
        var start = d.interval(then);
        d.activeLength = d.subinterval.count(start, d.interval.offset(start, 1));
        d.activeIndex = d.subinterval.count(start, then);
        d.angle = d.activeIndex / d.range.length * tau;
      })
      .attr("transform", function(d) { return "rotate(" + d.angle / pi * 180 + ")"; })
      .style("fill", function(d) { return color(d.angle); });

  fieldTick
      .classed("field-tick--disabled", function(d, i) { return i >= d.field.activeLength; })
      .classed("field-tick--active", function(d, i) { return i === d.field.activeIndex; });

  setTimeout(tick, delay);
})();

</script>