References
- Introductory Astronomy & Astrophysics (4th Edition), by
Zeilek & Gregory
- The Dynamic Universe (An introduction to Astronomy),
Theodore P. Snow
- Fundamental Astronomy (3rd Edition), by H. Kartlunen, P
Kroger, H. Oja, M. Poutanen & K. J. Bonner
- Universe (5th Edition), by Kaufmann & Freedman
- University of California, San diego - Centre for
Astrophysics & Space sciences
- NASA's Hubble Space Telescope picture gallery