High Quality Content by WIKIPEDIA articles! Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth`s atmosphere and of their physical and chemical properties" In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject.Astronomy focuses on celestial objects, space, and the physical universe as a whole. Observations of the Sun, Moon, stars, and planets have formed the basis of timekeeping and navigation.