The present book is a translation of the original German edition
(published in 1982) with some minor corrections and improvements. The
guide to sup- plementary and advanced literature given in the Appendix,
however, has been brought up to date. This book is addressed primarily
to students taking astronomy as a prin- cipal or subsidiary subject, and
to scientists of related fields, but amateur as- tronomers should also
be able to profit from it. For most chapters an elementary knowledge of
mathematics and physics will be sufficient, however, Chaps. 5 and 6
impose somewhat greater requirements. In addition the reader should
already be acquainted with the basic concepts of stellar physics as
treated in introduc- tory books, including the spectral types, the
system of stellar magnitudes and colours, absolute magnitudes and
luminosities, the Herlzsprung-Russell dia- gram and its interpretation.
A modem textbook should use SI units. On the other hand, the use of the
cgs system is still the prevailing custom in astrophysics - together
with the special units of astronomy: length is quoted in parsecs [pc],
mass in solar masses [M0] and time in years [a]. We have therefore
compromised and employed both cgs and SI units in this book, whichever
was the appropriate choice in each instance. A table for conversion of
cgs units into SI units and vice versa is given in the Appendix.