# Pulsars and neutron stars/Pulsar rotation measures

## Measuring pulsar rotation measures

Pulsar rotation measures (RMs) are measured by fitting the position angle of the linear polarization over a range of observing frequencies as:

${\displaystyle \psi ={\rm {RM}}\lambda ^{2}}$

where ${\displaystyle \lambda =c/f}$  where ${\displaystyle f}$  is the observing frequency.

Measured pulsar RMs vary, in part, because of the Earth's ionosphere. This ionospheric correction can be estimated using the International Reference Ionosphere (IRI) model.