Sin had a beard made of lapis lazuli and rode on a winged bull. The bull was one of his symbols, through his father, Enlil, "Bull of Heaven", along with the crescent and the tripod (which may be a lamp-stand). On cylinder seals, he is represented as an old man with a flowing beard and the crescent symbol. In the astral-theological system he is represented by the number 30 and the moon. This number probably refers to the average number of days (correctly around 29.53) in a lunar month, as measured between successive new moons.