moon.js

#!/usr/bin/env node

var suncalc = require('suncalc');
var phase = suncalc.getMoonIllumination(new Date()).phase;
var phases = [
  "🌑",
   "🌒", "🌒", "🌒", "🌒", "🌒", "🌒", "🌒",
  "🌓",
  "🌔", "🌔", "🌔", "🌔", "🌔", "🌔", "🌔",
  "🌕",
  "🌖", "🌖", "🌖", "🌖", "🌖", "🌖", "🌖",
  "🌗",
  "🌘", "🌘", "🌘", "🌘", "🌘", "🌘", "🌘",
  "🌚",
  "🌝"
];

stepPhase = function (phase, randomVal) {
  if (randomVal === undefined) {
    randomVal = 0.1;
  }
  var len = phases.length - 2;
  var rv = Math.round(phase * len) % len;
  if (Math.random() <= randomVal && rv === 0) {
    rv = 8;
  } else if (Math.random() <= randomVal && rv === 4) {
    rv = 9;
  }
  return rv;
}

console.log(phases[stepPhase(phase)]);

function test() {
  for (var i = 1; i <= 31; i++) {
    var phase = suncalc.getMoonIllumination(new Date(2014, 9, i)).phase;
    console.log("2014-09-" + i, phase, phases[stepPhase(phase)]);
  };
}

// test();