Is jQuery an Array?

I'm just getting into jQuery and I am having problems understanding what it is. How can I use array style indexing on a jQuery object but jQuery not be an array? Is this a javascript thing?

<ul id="myUL">
<li></li>
<li id="second"></li>
<li></li>
</ul>

var jqueryObject = $("#myUL > li");
alert(jqueryObject[1].attributes.getNamedItem("id").value);

if (jqueryObject instanceof Array) {
    alert('value is Array!');
} else {
    alert('Not an array');//this is what pops up
}