Astronomy is the scientific study of the Universe and its
contents. The Wikiversity Astronomy textbook is divided into
several units typical of introductory texts at the university
level. These units can be presented out of order, or some may be
omitted: This is the study of constellations, asterisms,
apparent diurnal and annual motions of the sun and stars, motion
and appearance of the moon, lunar and solar eclipses, lunar and
solar calendars, and stellar coordinate systems. Experts in this
field display a solid understanding of the three-dimensional
character of the solar system; the typical size and speed scales
involved; the relationship between angular size, actual size,
and distance; and the vocabulary needed to describe positions of
astronomical objects. This unit provides the background required
to understand the historical revolutions in astronomical
knowledge described in the next unit. This is the study of the
history of astronomy, in particular ancient (typically cross-
cultural) astronomy and its