In response to Dave Raines comments "Remember that the sweep angle is measured with respect to the 1/4 chord of the wing, not the leading or trailing edges". I wonder if that could be explained a little more?

From : Don Stackhouse

The aerodynamic center of an airfoil is typically at about 25% of the way back from the leading edge. This is the point on the airfoil that all the aerodynamic forces seem to act through. Therefore, when we are analyzing the aerodynamic characteristics of a flying surface, we typically measure everything from those local aerodynamic centers, the quarter-chord points along the surface.

The other term you sometimes hear (mainly in very old aero books and also in model aviation aero discussions) is "center of pressure", which is not the same thing as aerodynamic center. It is an archaic term, dating back to before the concept of aerodynamic pitching moment was fully understood, and is the result of crudely lumping together the lift vector with the aerodynamic pitching moment. The problem with center of pressure is that it moves depending on the angle of attack, and at some angles of attack it might even be somewhere well aft of the trailing edge! It's pretty hard to measure from a moving reference point, and therefore has limited usefulness. In full-scale aerodynamics the term center of pressure has been pretty much discarded.

Don Stackhouse
DJ Aerotech