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D3 Celestial Gelolocator: Night Sky

14 Jan 2020, 18:29 UTC
D3 Celestial Gelolocator: Night Sky
(200 words excerpt, click title or image to see full post)

[Previously: part I Geolocator, part II Sky color, part III Geomarker]

The next feature for the geolocator-globe, a plugin to display the current night hemisphere with increasing levels of darkness, depending on the state of twilight. The distinction is between civil twilight, which lasts from sunset until the sun is 6 degrees below the horizon, followed by nautical twilight until 12 degrees and finally astronomical twilight lasting to 18 degrees below. In reverse order the same is true for dawn. The subsolar point, where the Sun is directly above, is market with a small yellow circle.

A small update for the Geomarker plugin as well, where the marker is invisible when the current position on the globe is rotated out of view.

// This plugin shows concentric hemispheres with increasing opacities,
// specifically to show the dark side with increasing levels of twilight.
function hemisphere(options) {
var pos = {},
options = options || {};

options.color = options.color || 'black';
options.alpha = options.alpha || 0.12;

// Current antisolar point, directly opposite of the Sun
var setOrigin = function(lng, lat) {
pos.lng = lng;
pos.lat = lat;
...

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