function calendar(calendarDay) {
	if (calendarDay == null) calDate = new Date()
	else calDate = new Date(calendarDay);
	document.write ("<table id='calendar_table'>");
	writeCalTitle(calDate);
	writeDayNames();
	writeCalDays(calDate);
	document.write ("</table>");
	}
	
function writeCalTitle(calendarDay) {
	var monthName = new Array("January", "February", "March", "April", "May", "June","July", "August", "September", "October", "November", "December" );
	var thisMonth=calendarDay.getMonth();
	var thisYear =calendarDay.getFullYear();
	document.write("<tr>");
	document.write("<th id='calendar_head' colspan ='7'>");
	document.write(monthName[thisMonth]+" "+thisYear);
	document.write("</th>");
	document.write("</tr>");
	}
function writeDayNames(){
	var dayName= new Array("Sun", "Mon", "Tues", "Wed", "Thurs", "Fri", "Sat");
	document.write("<tr>");
	for (var i=0; i<dayName.length; i++){
	document.write("<th class='calendar_weekdays'>"+dayName[i]+"</th>");}
	document.write("</tr>");
}
function daysInMonth(calendarDay){
	var thisYear=calendarDay.getFullYear();
	var thisMonth=calendarDay.getMonth();
	var dayCount= new Array(31,28,31,30,31,30,31,31,30,31,30,31);
	if(thisYear % 4 ==0) {
		if((thisYear % 100 !=0) || (thisYear % 400 ==0)){
			dayCount[1] =29;//this is a leap year
			}}
	return dayCount[thisMonth];  //return the number of days in the month
	}
function writeCalDays(calendarDay){
	//determine the starting day of the week
	var currentDay = calendarDay.getDate();
	var dayCount = 1; 	
	var totalDays = daysInMonth(calendarDay);    // set the date to the first day of the month
	calendarDay.setDate(1);
	var weekDay = calendarDay.getDay();  //the day of the wwk of the first day
	
	//write blank cells preceding the starting day
	document.write("<tr>");
	for (var i=0; i <weekDay; i++){
		document.write("<td></td>");
	}
	while (dayCount <= totalDays){
		///write the table rows and cells
		if(weekDay == 0) document.write("<tr>");
		
		if (dayCount == currentDay){
			document.write("<td class='calendar_dates' id='calendar_today'>"+dayCount+"</td>");}
			else {
				document.write("<td class='calendar_dates'>"+dayCount+"</td>");}
		if (weekDay == 6)document.write("</tr>");
		
		//move to the next day
		dayCount++;
		calendarDay.setDate(dayCount);
		weekDay = calendarDay.getDay();
	}
		document.write("</tr>");
		}