Vaidate a date in Rails

Need to validate that the date entered is a certain day of the week.

View:
   
      <div class="form inline">
       <%= f.label :meeting_date, "Meeting Date" %>
      <%= f.date_select :meeting_date, :class => 'form_control date_select datetest'  %>
      </div>
     

I am looking for a way to validate that this "meeting_date" is valid and a particular day of the week.