many factors, but key problems are the uncertainty surrounding the observation methods used to develop and populate the diagonal star tables, and the criteria used to select decans (brightness, position, relationship with other stars, and so on). Later developments These predictable heliacal re-appearances by the decans were eventually used by the Egyptians to mark the divisions of their annual solar calendar. Thus the heliacal rising of Sirius marked the annual flooding of the Nile. This method led to a system of 12 daytime hours and 12 nighttime hours, varying in length according to the season. Later, a system of 24 "equinoctial" hours was used. After Hellenistic astrology arose in Alexandria, recorded principally in the work of Claudius Ptolemy and Vettius Valens, various systems attributing symbolic significance to decans arose and linked these to the "wandering stars" and the "Lights": the Sun, Moon, Mercury Venus, Mars as well as Jupiter and Saturn. Decans were connected, for example, with the winds, the four directions, the sect (day or night,) male and female, as well as the four humours (elements;) also these were hermetically considered linked with various diseases and with the timing for the engraving of talismans for curing them; with decanic "faces" (or "phases"), a system where three decans are assigned to each zodiacal sign, each covering 10° of the zodiac, and each ruled by a planetary ruler (see Decan (astrology)); and correlated with astrological signs. Descriptions of the decans Decans are named in various Greco-Egyptian sources, many Hermetic writings, the Testament of Solomon, and the writings of Aristobulus of Paneas. Julius Firmicus Maternus, Cosmas of Maiuma, Joseph Justus Scaliger, and Athanasius Kircher. Images of the decans are described in Hermetic writings, by the Indian astrologer Varāhamihira, in the Picatrix, and in Japanese writings. Varāhamihira's images of the decans was influenced by Greco-Egyptian, if not Hermetic, depictions of the decans by way of the Yavanajataka. Their role in Japanese astrology may have derived from an earlier Chinese or Indian form possibly from adding the twelve animals of the Chinese zodiac to a list of twenty-four hour stars. They were most common between the Kamakura and Edo periods. The first original decan position due to the precession in ancient times started at 0° of Cancer when the heliacal rising of Sirius (Egyptian Sepdet; Greco-Egyptian: Sothis) on sunset like Jewish and Islamic calendars marking the Egyptian New Year and now the 1st decan