JS/CSS Moon Phases snippet

Simple script to generate moon phases ( https://en.wikipedia.org/wiki/Lunar_phase )

It uses 2 SVG (2 hemispheres) and some CSS transformation.

You can avoid JS if you don’t need real-time phase update.

HTML code

<div class="moon">
  <svg height="200" width="100" class="moon-left">
    <circle cx="100" cy="100" r="100" stroke="white" fill="white" class="bg"/>
    <circle cx="100" cy="100" r="100" stroke="white" fill="black" class="fg"/>
  </svg><svg height="200" width="100" class="moon-right">
    <circle cx="0" cy="100" r="100" stroke="white" fill="white" class="bg"/>
    <circle cx="0" cy="100" r="100" stroke="white" fill="black" class="fg"/>
  </svg>
  
  <div id="phase"></div>
</div>

 

CSS

html, body {width:100%;background-color:#333;margin:0;position:relative; font: 1em sans-serif;}
.moon {width:200px;margin:2rem auto;}
#phase {width:200px;margin:25px 0;}

.moon-left,.moon-right {display:inline-block;width:100px;position:relative;margin:0;}
.moon-left .bg,.moon-right .bg {stroke-width:2px;}

.moon-right .fg {stroke-width:2px;}
.moon-left .bg {fill:black;}
.moon-left .fg {fill:white;transform-origin: 0% 0%;}

.moon-right .fg {transform: scaleX(1);}
.moon-left .fg {transform: scaleX(0) translateX(0);}

 

and JS code. The code is prolix and redundant, but it helps to understand what happens.

jQuery( "#phase" ).slider({
      min: 0,
      max: 200,
      value: 2,
      step:10,
      slide: function( event, ui ) {
        updateMoon( ui.value );
      }
  });

Math.radians = function(degrees) {
  return degrees * Math.PI / 180;
};
function updateMoon(phase){
  var phaseScale = 1,
      phaseTrans = 100,
      phaseRight = 0;
  
  if(phase <= 100) {
    phaseRight = (1-phase/100);
  } 
  jQuery('.moon-right .fg').css({
    'transform':'scaleX(' + phaseRight + ')'
  });
  
  if(phase >= 100) {
    phaseScale = (1-(phase-100)/100);
    phaseTrans = 100*phaseScale;
  } 
  jQuery('.moon-left .fg').css({
    'transform':'translate('+phaseTrans+'px,0) scaleX(' + (1-phaseScale) + ')'
  });
  
}

 

and here the result JS/CSS Moon Phases

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