In honor of the vernal equinox, this animation shows the progression of the solar terminator at approximately 5.2 million times its normal rate. Each frame of the animation advances twenty-four hours ahead of real-time so that the seasonal changes of the solar terminator are visible. The blue region is night; the white region is day. Best accompanied with the theme song from Buck Rogers.
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| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <style> | |
| body { | |
| background: #fcfcfa; | |
| } | |
| .stroke { | |
| fill: none; | |
| stroke: #000; | |
| stroke-width: 3px; | |
| } | |
| .fill { | |
| fill: #fff; | |
| } | |
| .graticule { | |
| fill: none; | |
| stroke: #777; | |
| stroke-width: .5px; | |
| stroke-opacity: .5; | |
| } | |
| .land { | |
| fill: #222; | |
| } | |
| .boundary { | |
| fill: none; | |
| stroke: #fff; | |
| stroke-width: .5px; | |
| } | |
| .night { | |
| stroke: steelblue; | |
| fill: steelblue; | |
| fill-opacity: .3; | |
| } | |
| text { | |
| font-family: Menlo, monospace; | |
| } | |
| </style> | |
| <body> | |
| <script src="http://d3js.org/d3.v3.min.js"></script> | |
| <script src="http://d3js.org/d3.geo.projection.v0.min.js"></script> | |
| <script src="http://d3js.org/topojson.v1.min.js"></script> | |
| <script> | |
| var width = 960, | |
| height = 570; | |
| var π = Math.PI, | |
| radians = π / 180, | |
| degrees = 180 / π; | |
| var formatDate = d3.time.format.utc("%b. %d, %Y"), | |
| formatTime = d3.time.format.utc("%X UTC"); | |
| var circle = d3.geo.circle() | |
| .angle(90); | |
| var projection = d3.geo.kavrayskiy7() | |
| .scale(170) | |
| .translate([width / 2, height / 2]) | |
| .precision(.1); | |
| var path = d3.geo.path() | |
| .projection(projection); | |
| var graticule = d3.geo.graticule(); | |
| var svg = d3.select("body").append("svg") | |
| .attr("width", width) | |
| .attr("height", height); | |
| svg.append("defs").append("path") | |
| .datum({type: "Sphere"}) | |
| .attr("id", "sphere") | |
| .attr("d", path); | |
| svg.append("use") | |
| .attr("class", "stroke") | |
| .attr("xlink:href", "#sphere"); | |
| svg.append("use") | |
| .attr("class", "fill") | |
| .attr("xlink:href", "#sphere"); | |
| var g = svg.append("g"); | |
| g.append("path") | |
| .datum(graticule) | |
| .attr("class", "graticule") | |
| .attr("d", path); | |
| d3.json("/mbostock/raw/4090846/world-50m.json", function(error, world) { | |
| var dayOffset = 0; | |
| var date = svg.append("text") | |
| .attr("dy", "-1.35em"); | |
| var time = svg.append("text"); | |
| svg.selectAll("text") | |
| .attr("x", 16) | |
| .attr("y", height - 16); | |
| g.insert("path", ".graticule") | |
| .datum(topojson.feature(world, world.objects.land)) | |
| .attr("class", "land") | |
| .attr("d", path); | |
| g.insert("path", ".graticule") | |
| .datum(topojson.mesh(world, world.objects.countries, function(a, b) { return a !== b; })) | |
| .attr("class", "boundary") | |
| .attr("d", path); | |
| var night = svg.append("path") | |
| .attr("class", "night"); | |
| d3.timer(function() { | |
| var now = new Date(Date.now() + dayOffset); | |
| date.text(formatDate(now)); | |
| time.text(formatTime(now)); | |
| night.datum(circle.origin(antipode(solarPosition(now)))).attr("d", path); | |
| dayOffset += 864e5; | |
| }); | |
| }); | |
| d3.select(self.frameElement).style("height", height + "px"); | |
| function antipode(position) { | |
| return [position[0] + 180, -position[1]]; | |
| } | |
| 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); | |
| } | |
| </script> |
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