khan academy - How can i make a circular motion in javascript -

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i'm trying make solar system using javascript, , i'm using khan academy make it, font know how can make them move in circle around sun kept browsing net hours, couldn't find anything. here's project can see have done , can in it

https://www.khanacademy.org/computer-programming/solar-system/6120244512161792

just started:

x = 100  // center  y = 50   // center  r = 50   // radius  = 0    // angle (from 0 math.pi * 2)    function rotate(a) {        var px = x + r * math.cos(a); // <-- that's maths need    var py = y + r * math.sin(a);        document.queryselector('#point').style.left = px + "px";    document.queryselector('#point').style.top = py + "px";    }      setinterval(function() {    = (a + math.pi / 360) % (math.pi * 2);    rotate(a);  }, 5);
div {    position: fixed;    width: 10px;    height: 10px;  }    #center {    left: 100px;    top: 50px;    background: black;  }    #point {    left: 0px;    top: 0px;    background: red;  }
<div id="center"></div>  <div id="point"></div>


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