 Tolkien's only mention of the Dwarves' calendar is in "The Hobbit", regarding the "dwarves' New Year" or "Durin's Day".Astronomer Bradley E. Schaefer has analysed the astronomical determinants of Durin's Day.He concluded that – as with many real-world lunar calendars – the date of Durin's Day is observational, dependent on the first visible crescent moon.