custom map v3

    var mapTypes = [];

    mapTypes['sky'] = {
      getTileUrl: function(coord, zoom) {
        return getHorizontallyRepeatingTileUrl(coord, zoom, function(coord, zoom) {
          return "http://mw1.google.com/mw-planetary/sky/skytiles_v1/" +
                 coord.x + "_" + coord.y + '_' + zoom + '.jpg';

        });
      },
      tileSize: new google.maps.Size(256, 256),
      isPng: false,
      maxZoom: 10,
      radius: 57.2957763671875,
      name: 'Sky',
      credit: 'Image Credit: SDSS, DSS Consortium, NASA/ESA/STScI'
    };

    function getHorizontallyRepeatingTileUrl(coord, zoom, urlfunc) {
      var y = coord.y;
      var x = coord.x;

      var tileRange = 1 << zoom;

      if (y < 0 || y >= tileRange) {
        return null;
      }

      if (x < 0 || x >= tileRange) {
        x = (x % tileRange + tileRange) % tileRange;
      }

      return urlfunc({x:x,y:y}, zoom)
    }

    function getMarsTileUrl(baseUrl, coord, zoom) {
      var bound = Math.pow(2, zoom);
      var x = coord.x;
      var y = coord.y;
      var quads = ['t'];

      for (var z = 0; z < zoom; z++) {
        bound = bound / 2;
        if (y < bound) {
          if (x < bound) {
            quads.push('q');
          } else {
            quads.push('r');
            x -= bound;
          }
        } else {
          if (x < bound) {
            quads.push('t');
            y -= bound;
          } else {
            quads.push('s');
            x -= bound;
            y -= bound;
          }
        }
      }

      return baseUrl + quads.join('') + ".jpg";
    }

    var map;
    var mapTypeIds = [];

    function initialize() {

      for (var key in mapTypes) {
        mapTypeIds.push(key);
      }

      var mapOptions = {
        zoom: 0,
        center: new google.maps.LatLng(0, 0),
        mapTypeControlOptions: {
          mapTypeIds: mapTypeIds,
          style: google.maps.MapTypeControlStyle.DROPDOWN_MENU
        }
      };
      map = new google.maps.Map(document.getElementById("map_canvas"), mapOptions);

      for (key in mapTypes) {
        map.mapTypes.set(key, new google.maps.ImageMapType(mapTypes[key]));
      }

      map.setMapTypeId('sky');
    }