Libellus ysagogicus, 1491
Alchabitius (ʻAbd al-ʻAzīz Ibn ʻUthmān) was a 10th century Arabian astrologer whose work, as translated in the 15th century by John of Seville, was intended as an introductory text to astronomy and astrology. Libellus ysagogicus (Mudkhal ilá ṣināʻat aḥkām al-nujūm) includes many horoscopes as well as explanation on the relation of the planets to bodily infirmity. During the Renaissance, horoscopes commonly assumed a structured rectangular configuration like those seen in Libellus ysagogicus. Zodiacal symbols can be seen within the margin of the box enclosing the horoscope. Each triangle represents one of the twelve constellations of the zodiac, beginning with the triangle to the immediate left of center and proceeding counter-clockwise. Within the triangles, symbols of the planets, sun, and moon denote where they appear on the ecliptic (the apparent circle on the celestial sphere along which the sun, moon, and planets seem to move). Usually, the square in the middle was left blank for the astrologer to record key details about the person for whom the horoscope was prepared. The mathematical calculation of the horoscope had to be precise: the horoscope shows the configuration of the planets (the sun and moon were considered planets) at a precise moment for a given location on earth. With this information, the astrologer renders a judgment. To properly interpret the meaning of the celestial configuration, the astrologer must weigh many considerations including the properties of the planets themselves (male or female, wet or dry, hot or cold) and the influences of particular configurations of planets. Casting horoscopes employed an arcane vocabulary of planetary influences such as dignity, combust, exaltation, and caput and cauda draconis. Two of the images shown here are examples of horoscopes; the third is a representation of the celestial sphere. For a description of the sphere, see: Sphaera mundi, 1490.