William C. Keel 
The Sky at Einstein’s Feet [PDF ebook] 

The sky at Einstein’s feet.- Bookkeeping at the speed of light.- Relativistic Matter.- From shifting stars to multiple quasars.- Through the gravitational telescope.- The stars themselves.- Extreme spacetime bending: black holes.- The shape of Einstein’s Universe.- The view from Einstein’s shoulders.

Bill Keel, the author of The Road to Galaxy Formation (Springer-Praxis 2002), has been involved in many areas of extragalactic astronomy, and for the last 18 years has worked at the University of Alabama. Of particular relevance to this book is his study of gravitational lensing since 1980, early calculations on microlensing of quasars, and an ongoing Hubble survey for gravitational lensing effects in silhouetted galaxies as a constraint on massive dark-matter candidates. His experience in serving on 16 NASA review committees for various space-astrophysics missions and higher-level programmatic issues has broadened his view of relativity in astronomy triggering the idea for this book.