Regular expression to require a space in user name
 

Participants on our forum are required to use real names, first and last, as a user name. The user expression we are using is
Code:
^[A-Z ]+$
Can someone help me with an expression that would look for two names with a space between. In other words, it would refuse "JoeSmith" and accept "Joe Smith."

Thanks in advance for any helpful replies.