According to Diodorus, it was believed that a particular star or constellation presided over the birth of each person, and thenceforward exercised over his life a special malign or benignant influence.

But his lot depended, not on this star alone, but on the entire aspect of the heavens at a certain moment.

To cast the horoscope was to reproduce this aspect, and then to read by means of it the individual's future.
Chaldee astrology, was not, however, limited to genethlialogy.

The Chaldaeans professed to predict from the stars such things as the changes of the weather, high winds and storms, great heats, the appearance of comets, eclipses, earthquakes, and the like.

They published lists of luck and unlucky days, and tables showing what aspect of the heavens portended good or evil to particular countries.