  Since more than a century astronomers measure the position angle of the major
axis of the polarization ellipse starting from the North direction and
increasing counter-clockwise, when looking at the source. This convention has
been enforced by the IAU with a Resolution in 1973. Much later the WMAP
satellite, which has observed the polarization of the cosmic microwave
background, has unfortunately adopted the opposite convention: the polarization
position angle is measured starting from the South and increasing clockwise,
when looking at the source. This opposite convention has been followed by most
cosmic microwave background polarization experiments and is causing obvious
problems and misunderstandings. The attempts and prospects to enforce the
official IAU convention are described.
