Measuring the Magnetic Field in the Solar Corona

The corona is the outermost layer of the Sun's atmosphere. Remarkably, it has a temperature of 1-2 million degrees Kelvin, while the layers of gases in the photosphere only a few thousand kilometers below (which we
see as the disk of the Sun) have a temperature of about 6000 K. The structure of the corona is partly determined by a magnetic field, as may be seen in pictures of solar eclipses. This magnetic field is widely
believed to play a role in the heating of the corona, either directly via Joule heating or indirectly via the damping of waves and turbulence which involve the magnetic field. Assessing this role requires measurements of the strength and structure of the coronal magnetic field. I will describe ways in which such information can be obtained by radioastronomical measurements. The physical effect at the basis of
these measurements is Faraday Rotation, consisting of a rotation of the plane of polarization of a radio wave when it propagates through an ionized gas with a magnetic field.

Dr. Steven R. Spangler

University of Iowa