Karl J. Donner & Hannu Karttunen 
Fundamental Astronomy [PDF ebook] 

Fundamental Astronomy gives a well-balanced and comprehensive introduction to the various fields of classical and modern astronomy. While emphasizing both the astronomical concepts and the underlying physical principles, the text provides a sound basis for more profound studies in the astronomical sciences. The present corrected printing of the revised and enlarged third edition of this successful textbook includes a host of new knowledge acquired in recent years. In particular the chapters on observations and on the physics of the Sun have been thoroughly revised.