In Norse mythology, Hjúki and Bil are a brother and sister who follow Máni (the moon personified) across the sky. They are described in the Prose Edda, written in the 13th century by Snorri Sturluson. Theories claim that the two gods' roles in mythology are the moon's phases. It is said that the two children were carrying a pail of water from a sacred well and that Máni swooped down and took the pail. The two children chase after Máni to attempt to take back their pail.