Cita APA

(2007).  21st century astronomy Jeff Hester ... [et al].  Norton.

Chicago Style Citation

 21st Century Astronomy Jeff Hester ... [et Al].  Norton, 2007.

Cita MLA

 21st Century Astronomy Jeff Hester ... [et Al].  Norton, 2007.

Atenció: Aquestes cites poden no estar 100% correctes.