Besides the unambiguously identifiable depictions of the zodiacal belt, four conventional Egyptian asterisms, and the planets, the other signs that feature in the two Dendera zodiacs are shown to derive from traditional Egyptian representational systems. These images, together with the accompanying figures of the decans, are incorporated into the design of the monuments to record celestial events and related cultic acts that tell the story of Osirisís death and resurrection, the conception of Isis from her deceased husband, and the nativity of their child, Horus. The astral aspects of these myths are connected with the phases of the moon, the yearly solar cycle, and the annual dawn rising of the star Sirius. The zodiacs are thus not catalogues of constellations but peculiar sky charts devised at specific moments of time that correspond to the coincidence of the full moon with the autumnal equinox in the years 52 BCE and 36 CE.