Written by a 15th century mathematician and physician, Giovanni Abiosi, this dialog in defense of astrology was intended as a general overview on the subject. Dialogus in Astrologie defensionem includes several charts and diagrams, but this edition is noted for the title page block print which shows an allegory of astrology. Urania, muse of astronomy, is the nude woman whose eyes are uplifted to the heavens. The central figure, Astrologia, holds two tools important to astronomical learning which were applied to astrology, during the Renaissance a legitimate astronomical pursuit. Her upraised arm holds an astrolabe, the displayed side of which shows a computer for determining a variety of celestial phenomena including times of sunrise and sunset for any day, the positions of bright stars, and many other uses. Precise time-telling is essential to astrology. Astrologia's left arm holds the essential teaching tool for astronomy, the armillary sphere, which shows the basic celestial reference circles against which the apparent movements of the sun, moon, and planets are measured. For another image and description of the armillary sphere, see: Sphaera mundi, 1490. Geographer and astronomer Claudius Ptolemy (second century AD) looks on at right, holding a copy of his treatise about celestial motions known as the Almagest, a page open to a depiction of the armillary sphere.