var name					= "#sidebar";
var sidebar_top_limit 		= 422;
var sidebar_top_margin 		= 20;
var sidebar_slide_duration	= 500;

$(window).scroll(function() { 
	// Calculates the top offset adds the limit
	offset = $(document).scrollTop() + sidebar_top_margin;

	// This keeps the sidebar away from the top of the page
	if(offset < sidebar_top_limit)
		offset = sidebar_top_limit;
	
	// Animation
	$(name).animate({top:offset},{duration:sidebar_slide_duration,queue:false});
});