The galactic magnetic field

Estimates for the scale, geometry and strength of the magnetic field in the galactic system can be derived from observations of polarization properties of radio emission from the Galaxy, extragalactic radio sources and pulsars, and polarization of starlight. Within distances of about 500 parsecs (1 parsec = 3.26 lightyears) from the solar system the magnetic field is directed towards galactic longitude $I\approx45^\circ$, while at distances extending over a few kiloparsec its average direction is towards $I\approx90^\circ$. Seen on a large scale the magnetic field in the Galaxy may be directed parallel to the galactic plane and along the spiral arms. The field may consist of a regular component and a random component with small scale variations of about 50 parsec in size. The strength of both components is of the same order of magnitude, about $2\times10^{-6}$ Gauss (this is about $6\times10^{-6}$ times the magnetic field strength of the earth).