mbostock · March 10, 2019 08:11
diff --git a/.block b/.block
 license: gpl-3.0
 redirect: https://observablehq.com/@mbostock/the-suns-view-of-the-earth
diff --git a/README.md b/README.md
diff --git a/index.html b/index.html
 <!DOCTYPE html>
 <meta charset="utf-8">
 <style>

 body {
  background: #fcfcfa;
 }

 .sun {
  fill: red;
 }

 .stroke {
  fill: #fff;
  stroke: #000;
  stroke-width: 1.5px;
 }

 .land {
  fill: #222;
 }

 </style>
 <body>
 <script src="//d3js.org/d3.v3.min.js"></script>
 <script src="//d3js.org/topojson.v1.min.js"></script>
 <script>

 var width = 960,
    height = 960;

 var π = Math.PI,
    radians = π / 180,
    degrees = 180 / π;

 var projection = d3.geo.orthographic()
    .clipAngle(90)
    .scale(475)
    .translate([width / 2, height / 2])
    .precision(.1);

 var path = d3.geo.path()
    .projection(projection);

 var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

 svg.append("circle")
    .attr("class", "stroke")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")")
    .attr("r", projection.scale());

 svg.append("circle")
    .attr("class", "sun")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")")
    .attr("r", 2.5);

 d3.json("/mbostock/raw/4090846/world-50m.json", function(error, world) {
  if (error) throw error;

  var land = svg.insert("path", ".sun")
      .datum(topojson.feature(world, world.objects.land))
      .attr("class", "land")
      .attr("d", path);

  redraw();
  setInterval(redraw, 1000);

  function redraw() {
    var position = solarPosition(new Date);
    projection.rotate([-position[0], -position[1]]);
    land.attr("d", path);
  }
 });

 function solarPosition(time) {
  var centuries = (time - Date.UTC(2000, 0, 1, 12)) / 864e5 / 36525, // since J2000
      longitude = (d3.time.day.utc.floor(time) - time) / 864e5 * 360 - 180;
  return [
    longitude - equationOfTime(centuries) * degrees,
    solarDeclination(centuries) * degrees
  ];
 }

 // Equations based on NOAA’s Solar Calculator; all angles in radians.
 // http://www.esrl.noaa.gov/gmd/grad/solcalc/

 function equationOfTime(centuries) {
  var e = eccentricityEarthOrbit(centuries),
      m = solarGeometricMeanAnomaly(centuries),
      l = solarGeometricMeanLongitude(centuries),
      y = Math.tan(obliquityCorrection(centuries) / 2);
  y *= y;
  return y * Math.sin(2 * l)
      - 2 * e * Math.sin(m)
      + 4 * e * y * Math.sin(m) * Math.cos(2 * l)
      - 0.5 * y * y * Math.sin(4 * l)
      - 1.25 * e * e * Math.sin(2 * m);
 }

 function solarDeclination(centuries) {
  return Math.asin(Math.sin(obliquityCorrection(centuries)) * Math.sin(solarApparentLongitude(centuries)));
 }

 function solarApparentLongitude(centuries) {
  return solarTrueLongitude(centuries) - (0.00569 + 0.00478 * Math.sin((125.04 - 1934.136 * centuries) * radians)) * radians;
 }

 function solarTrueLongitude(centuries) {
  return solarGeometricMeanLongitude(centuries) + solarEquationOfCenter(centuries);
 }

 function solarGeometricMeanAnomaly(centuries) {
  return (357.52911 + centuries * (35999.05029 - 0.0001537 * centuries)) * radians;
 }

 function solarGeometricMeanLongitude(centuries) {
  var l = (280.46646 + centuries * (36000.76983 + centuries * 0.0003032)) % 360;
  return (l < 0 ? l + 360 : l) / 180 * π;
 }

 function solarEquationOfCenter(centuries) {
  var m = solarGeometricMeanAnomaly(centuries);
  return (Math.sin(m) * (1.914602 - centuries * (0.004817 + 0.000014 * centuries))
      + Math.sin(m + m) * (0.019993 - 0.000101 * centuries)
      + Math.sin(m + m + m) * 0.000289) * radians;
 }

 function obliquityCorrection(centuries) {
  return meanObliquityOfEcliptic(centuries) + 0.00256 * Math.cos((125.04 - 1934.136 * centuries) * radians) * radians;
 }

 function meanObliquityOfEcliptic(centuries) {
  return (23 + (26 + (21.448 - centuries * (46.8150 + centuries * (0.00059 - centuries * 0.001813))) / 60) / 60) * radians;
 }

 function eccentricityEarthOrbit(centuries) {
  return 0.016708634 - centuries * (0.000042037 + 0.0000001267 * centuries);
 }

 d3.select(self.frameElement).style("height", height + "px");

 </script>
diff --git a/thumbnail.png b/thumbnail.png
	license: gpl-3.0
	redirect: https://observablehq.com/@mbostock/the-suns-view-of-the-earth
	<!DOCTYPE html>
	<meta charset="utf-8">
	<style>

	body {
	background: #fcfcfa;
	}

	.sun {
	fill: red;
	}

	.stroke {
	fill: #fff;
	stroke: #000;
	stroke-width: 1.5px;
	}

	.land {
	fill: #222;
	}

	</style>
	<body>
	<script src="//d3js.org/d3.v3.min.js"></script>
	<script src="//d3js.org/topojson.v1.min.js"></script>
	<script>

	var width = 960,
	height = 960;

	var π = Math.PI,
	radians = π / 180,
	degrees = 180 / π;

	var projection = d3.geo.orthographic()
	.clipAngle(90)
	.scale(475)
	.translate([width / 2, height / 2])
	.precision(.1);

	var path = d3.geo.path()
	.projection(projection);

	var svg = d3.select("body").append("svg")
	.attr("width", width)
	.attr("height", height);

	svg.append("circle")
	.attr("class", "stroke")
	.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")")
	.attr("r", projection.scale());

	svg.append("circle")
	.attr("class", "sun")
	.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")")
	.attr("r", 2.5);

	d3.json("/mbostock/raw/4090846/world-50m.json", function(error, world) {
	if (error) throw error;

	var land = svg.insert("path", ".sun")
	.datum(topojson.feature(world, world.objects.land))
	.attr("class", "land")
	.attr("d", path);

	redraw();
	setInterval(redraw, 1000);

	function redraw() {
	var position = solarPosition(new Date);
	projection.rotate([-position[0], -position[1]]);
	land.attr("d", path);
	}
	});

	function solarPosition(time) {
	var centuries = (time - Date.UTC(2000, 0, 1, 12)) / 864e5 / 36525, // since J2000
	longitude = (d3.time.day.utc.floor(time) - time) / 864e5 * 360 - 180;
	return [
	longitude - equationOfTime(centuries) * degrees,
	solarDeclination(centuries) * degrees
	];
	}

	// Equations based on NOAA’s Solar Calculator; all angles in radians.
	// http://www.esrl.noaa.gov/gmd/grad/solcalc/

	function equationOfTime(centuries) {
	var e = eccentricityEarthOrbit(centuries),
	m = solarGeometricMeanAnomaly(centuries),
	l = solarGeometricMeanLongitude(centuries),
	y = Math.tan(obliquityCorrection(centuries) / 2);
	y *= y;
	return y * Math.sin(2 * l)
	- 2 * e * Math.sin(m)
	+ 4 * e * y * Math.sin(m) * Math.cos(2 * l)
	- 0.5 * y * y * Math.sin(4 * l)
	- 1.25 * e * e * Math.sin(2 * m);
	}

	function solarDeclination(centuries) {
	return Math.asin(Math.sin(obliquityCorrection(centuries)) * Math.sin(solarApparentLongitude(centuries)));
	}

	function solarApparentLongitude(centuries) {
	return solarTrueLongitude(centuries) - (0.00569 + 0.00478 * Math.sin((125.04 - 1934.136 * centuries) * radians)) * radians;
	}

	function solarTrueLongitude(centuries) {
	return solarGeometricMeanLongitude(centuries) + solarEquationOfCenter(centuries);
	}

	function solarGeometricMeanAnomaly(centuries) {
	return (357.52911 + centuries * (35999.05029 - 0.0001537 * centuries)) * radians;
	}

	function solarGeometricMeanLongitude(centuries) {
	var l = (280.46646 + centuries * (36000.76983 + centuries * 0.0003032)) % 360;
	return (l < 0 ? l + 360 : l) / 180 * π;
	}

	function solarEquationOfCenter(centuries) {
	var m = solarGeometricMeanAnomaly(centuries);
	return (Math.sin(m) * (1.914602 - centuries * (0.004817 + 0.000014 * centuries))
	+ Math.sin(m + m) * (0.019993 - 0.000101 * centuries)
	+ Math.sin(m + m + m) * 0.000289) * radians;
	}

	function obliquityCorrection(centuries) {
	return meanObliquityOfEcliptic(centuries) + 0.00256 * Math.cos((125.04 - 1934.136 * centuries) * radians) * radians;
	}

	function meanObliquityOfEcliptic(centuries) {
	return (23 + (26 + (21.448 - centuries * (46.8150 + centuries * (0.00059 - centuries * 0.001813))) / 60) / 60) * radians;
	}

	function eccentricityEarthOrbit(centuries) {
	return 0.016708634 - centuries * (0.000042037 + 0.0000001267 * centuries);
	}

	d3.select(self.frameElement).style("height", height + "px");

	</script>