APA
zeilik m., gregory s., . (1998). introductory astronomy and astrphysics. fort worth: saunders college publishing.
Chicago
zeilik michael, gregory stephen, . 1998. introductory astronomy and astrphysics. fort worth: saunders college publishing.
Harvard
zeilik m., gregory s., . (1998). introductory astronomy and astrphysics. fort worth: saunders college publishing.
MLA
zeilik michael, gregory stephen, . introductory astronomy and astrphysics. fort worth: saunders college publishing. 1998.