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Arnor and Gondor used a Númenórean calendar called King's Reckoningbut even after the fall of Sauron at the end of that Age, the old calendar was maintained by the Exiles of Númenor in Middle-earth into the Third Age. When the era of the Kings passed with the fall of Arnor and the loss of King Eärnur, the King's Reckoning presented (through the continued accumulation of the millenial deficits) an offset of about 1.6 days out of synchronicity with the astronomical observations.
Steward Mardil made all months of equal length (30 days) and arranged the two days gained such symmetrically to the other holidays and also inserted two leap-days in T.A. 2059. However this still left a minor deficit of about 8 hours in advance. It is possible that the leap-day of 2060 was dropped in consequence.
In 2360 Steward Hador added 1 day to that year though this deficiency had not quite reached that amount being now a delay of only 0.3 day. By 3020 the deficit had once again accumulated to 0.77 days.
The Revised Calendar consisted of twelve months, each of thirty days, and five additional days that belonged to no month.
- Narwain, Ninui, Gwaeron
- tuilérë or Spring-day
- Gwirith, Lothron, Nórui
- loëndë (in leap-years replaced by two enderi)
- Cerveth, Úrui, Ivanneth
- yáviérë or Autumn-day
- Narbeleth, Hithui,Girithron
- Yestarë: Winter Solstice
- 28 Gwaeron: Vernal Equinox
- 30 Gwirith: Erukyermë
- Loëndë: Summer Solstice/Erulaitalë
- 10 October: Automnal Equinox
- ?? Eruhantalë