From ancient times, the Elves had dedicated the first day of the week to the stars: in Quenya it was named Elenya, and in Sindarin the equivalent form was Orgilion. These names found their way into archaic Mannish tongues as Sterrendei, and by the time of the War of the Ring, this form had evolved into 'Sterday'.

Sterday was the first day of the week, following the celebration and feasting of Highday, which closed the preceding seven days. By a peculiarity of the Hobbits' calendar, Sterday not only began each week, but also the entire year. The design of the Shire Calendar meant that each date always fell on the same weekday, so that 2 Yule, marking the beginning of the new year, always fell on the day of Sterday.