I have felt the need for a book on the theory of solar magnetic fields
for some time now. Most books about the Sun are written by observers or
by theorists from other branches of solar physics, whereas those on
magnetohydrodynamics do not deal extensively with solar applications. I
had thought of waiting a few decades before attempting to put pen to
paper, but one summer Josip Kleczek encouraged an im- mediate start
'while your ideas are still fresh'. The book grew out of a postgraduate
lecture course at St Andrews, and the resulting period of gestation or
'being with monograph' has lasted several years. The Sun is an amazing
object, which has continued to reveal completely unexpected features
when observed in greater detail or at new wavelengths. What riches would
be in store for us if we could view other stars with as much precision!
Stellar physics itself is benefiting greatly from solar discoveries,
but, in tum, our understanding of many solar phenomena (such as
sunspots, sunspot cycles, the corona and the solar wind) will
undoubtedly increase in the future due to their observation under
different conditions in other stars. In the 'old days' the solar
atmosphere was regarded as a static, plane-parallel structure, heated by
the dissipation of sound waves and with its upper layer expanding in a
spherically symmetric manner as the solar wind. Outside of sunspots the
magnetic field was thOUght to be unimportant with a weak uniform value
of a few gauss.