Sirius, known in ancient Egypt as Sopdet (Greek: Σῶθις Sothis), is recorded in the earliest astronomicalrecords. During the era of the Middle Kingdom, Egyptians based their calendar on the heliacal rising of Sirius, namely the day it becomes visible just before sunrise after moving far enough away from the glare of the Sun. This occurred just before the annual flooding of the Nile and the summer solstice,[28] after a 70-day absence from the skies.[29] The hieroglyph for Sothis features a star and a triangle. Sothis was identified with the great goddess Isis, who formed a part of a triad with her husband Osiris and their son Horus, while the 70-day period symbolised the passing of Isis and Osiris through the duat (Egyptian underworld).[29]