The conventions for the polarization angle

TL;DR

This paper discusses the inconsistency in polarization angle conventions used in astronomy, highlighting the conflict between the IAU standard and the WMAP satellite's approach, and explores efforts to unify these standards.

Contribution

It clarifies the differences in polarization angle conventions and discusses strategies to enforce the official IAU standard across astronomical observations.

Findings

The IAU standard for polarization angle measurement is well-established since 1973.

WMAP adopted the opposite convention, causing confusion in the field.

Efforts are ongoing to standardize the polarization angle convention internationally.

Abstract

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.