There are 2 ways you could do this:
1. Get the date from database utilities see MySQL documentation (I only know the Oracle commands)
2. In PHP you could do this
date("l", mktime(0,0,0,mm,dd,yyyy));
Cutting the month, day and year parts from your date string. This would return the day
e.g.
echo (date("l", mktime(0,0,0,4,8,2003)));
would return Tuesday.