var mapObj = new google.maps.Map(document.getElementById('map'), {
    zoom:1,
    center: new google.maps.LatLng(0,0),
    mapTypeId: google.maps.MapTypeId.ROADMAP
});

new DayNightOverlay({
    map: mapObj,
    fillColor: 'rgba(200,0,0,0.3)',
    date: new Date(Date.UTC(2012,0,1))
});