JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<svg width="400px" height="400px" viewBox="0 0 600 600">
<!-- a (rx ry x-axis-rotation large-arc-flag sweep-flag x y)+ -->
  <path class="moon" d="m100,0 
                              a15,20 0 1,0 0,150
                              a20,20 0 1,0 0,-150" 
    />
  <path class="moon" d="m300,0                                               
                         a15,20 0 1,1 0,150
                         a20,20 0 1,1 0,-150" 
    />
  <path class="moon" d="m100,200                                               
                         a15,20 0 1,0 0,150
                         a20,20 0 1,1 0,-150" 
    />  
<path class="moon" d="m300,200                                               
                         a15,20 0 1,1 0,150
                         a20,20 0 1,0 0,-150" 
    />      
</svg>
</html>

CSS

.moon { fill:none; stroke:black; stroke-width:2 }

JavaScript

// http://stackoverflow.com/questions/11759992/calculating-jdayjulian-day-in-javascript
// http://jsfiddle.net/gkyYJ/
// http://stackoverflow.com/users/965051/adeneo
Date.prototype.getJulian = function() {
    return Math.floor((this / 86400000) - (this.getTimezoneOffset()/1440) + 2440587.5);
}

// http://www.ben-daglish.net/moon.shtml
function moon_day(today) {
    var GetFrac = function(fr) { return (fr - Math.floor(fr));}
    var thisJD = today.getJulian();
    var year = today.getFullYear();
    var degToRad = 3.14159265 / 180;
    var K0, T, T2, T3, J0, F0, M0, M1, B1, oldJ;
    K0 = Math.floor((year-1900)*12.3685);
    T = (year-1899.5) / 100;
    T2 = T*T; T3 = T*T*T;
    J0 = 2415020 + 29*K0;
    F0 = 0.0001178*T2 - 0.000000155*T3 + (0.75933 + 0.53058868*K0) - (0.000837*T + 0.000335*T2);
    M0 = 360*(GetFrac(K0*0.08084821133)) + 359.2242 - 0.0000333*T2 - 0.00000347*T3;
    M1 = 360*(GetFrac(K0*0.07171366128)) + 306.0253 + 0.0107306*T2 + 0.00001236*T3;
    B1 = 360*(GetFrac(K0*0.08519585128)) + 21.2964 - (0.0016528*T2) - (0.00000239*T3);
    var phase = 0;
    var jday = 0;
    while (jday < thisJD) {
        var F = F0 + 1.530588*phase;
        var M5 = (M0 + phase*29.10535608)*degToRad;
        var M6 = (M1 + phase*385.81691806)*degToRad;
        var B6 = (B1 + phase*390.67050646)*degToRad;
        F -= 0.4068*Math.sin(M6) + (0.1734 - 0.000393*T)*Math.sin(M5);
        F += 0.0161*Math.sin(2*M6) + 0.0104*Math.sin(2*B6);
        F -= 0.0074*Math.sin(M5 - M6) - 0.0051*Math.sin(M5 + M6);
        F += 0.0021*Math.sin(2*M5) + 0.0010*Math.sin(2*B6-M6);
        F += 0.5 / 1440; 
        oldJ=jday;
        jday = J0 + 28*phase + Math.floor(F); 
        phase++;
    }

    // 29.53059 days per lunar month
    return (((thisJD-oldJ)/29.53059));
}

console.log(moon_day(new Date()));