Accessing variables within includes?

I’m quite new to PHP and need some help. I’ve got index.php which looks like this:


<?php
$sectionname = "index";
include "header.php";
?>

Then in header.php i’ve got:


<?php 
echo($sectionname);
?>

index.php displays blank (ie doesn’t echo $sectionname). How can i make a variable defined in index.php available in header.php?