This is a very simple example of AJAX using the Rico library, and PHP for the back end. When you change the selection, a request is made to getPlanet.php, for example getPlanet.php?planet=Mars.
"View source" in your browser to see the HTML/Javascript for this page. The PHP source for the back end is viewable here.
Source code and output placed in the public domain by John Hartnup, 2006
Planet fact:
Planet: .