Make a div appear when scrolling past a certain point of a page

Question

My goal is to make a fixed div appear at the top of a page once someone scrolls a certain amount of pixels down the page. Basically once the header section is out of view,

Answer 1

window.addEventListener("scroll",function() { 
   $('.fixedDiv')[(window.scrollY > 500)?"slideDown":"slideUp"]();
},false);

DEMO: http://jsfiddle.net/DerekL/8eG2A/