Magnetic Fields on the Sun

This chapter presents a general picture of magnetic fields on the Sun. Magnetic fields on the Sun were first measured in sunspots using the Zeeman splitting of spectral lines in the early twentieth century. After the invention of the photoelectric solar magnetograph in the mid-twentieth century, it became clear that magnetic fields are present almost everywhere in the photosphere, but they are distributed very unevenly. The strongest fields are observed inside active regions containing sunspot groups. Weaker fields are present in quiet regions of the Sun in the form of ephemeral regions, network fields, and intra-network fields. Although the presence of magnetic fields in the chromosphere and corona is manifested by their structure, direct measurements in these layers are still associated with many difficulties and uncertainties. Information about coronal magnetic fields is obtained mainly by extrapolation of measurements of the photospheric field into the corona in various approximations.