This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Lunar gathers the two calendars in this group that track the moon alone, with no correction to keep them aligned with the solar year, and the two differ almost completely in origin and standing.
The Islamic Calendar (Hijri) is the living calendar of well over a billion Muslims, twelve lunar months of about twenty nine or thirty days fixed by observing or calculating the new moon, used throughout the Muslim world to date Ramadan, the hajj and every other religious observance. Carrying no intercalation, its year runs to only about 354 or 355 days, so its dates shift roughly eleven days earlier against the Gregorian calendar each year, cycling through every season over about thirty three years.
The Celtic Tree Calendar looks superficially similar, thirteen lunar months each named for a tree, but its origin is recent and literary rather than ancient. Robert Graves set it out in his 1948 book The White Goddess, building it from tree names attached to letters of the Ogham alphabet in medieval Irish grammatical tracts; no medieval or ancient source presents those names as a calendar at all. It has nevertheless been taken up widely in modern Druidry, Wicca and popular astrology, a genuinely living scheme resting on an invented pedigree.
Together the two show that tracking the moon alone describes a mechanism, not a lineage: one calendar's authority rests on fourteen centuries of continuous religious practice, the other's on a single mid twentieth century book.