Geolocation and Haversine formula

Question

I am trying to create a basic web application that detects the users geolocation, queries a mySQL database, and returns all bus stops within say 5 kilometers.

The GTFS feed including the Longitude and Latitude have been inserted into a mySQL database, and I found a example HTML page that provides the Longitude and Latitude of the browser accessing the web application.

I am seeking some help writing the mySQL query that takes this information and returns the results.