Iah (Jꜥḥ, the Moon)

YAH

egyptian: Jꜥḥ

Definition

Iah — Egyptian Jꜥḥ, also written "iakh" or "jaH" — is the ancient Egyptian word for the Moon, and the lunar being it names. It covers both the visible Moon-disk and the lunar deity behind it. It is close to, but not the same as, Khonsu, the Theban moon-god you meet elsewhere in this glossary: Egyptologists often treat iah as the Moon itself and Khonsu as its cult-god, though the two overlap and iah is a divine being too. The same word also names the eighteenth day of the schematic lunar month — the Feast of the Moon.

In Tradition

Scholars read iah as the foundational lunar word that underpins Egyptian Moon-religion — the cult of Khonsu and Thoth, the timing of lunar festivals, and the schematic month built around the Moon's phases. Those phases carry their own names, usually identified as psḏntjw (the new-Moon day), dnjt (a quarter day, days 7 and 23), and smdt (the full Moon, day 15), though the exact readings are debated. The month ran about 29.5 days, alternating 30 and 29.

In Practice

When you read an Egyptian calendar or temple text, iah is the thread tying the Moon to the working year. The lunar month was a real schedule: day 1 was psḏntjw, when the old crescent vanished; day 15 (smdt) was the full Moon; day 18 was the Feast of the Moon, iah itself, sitting in the canonical thirty-day list that runs from psḏntjw through to prt-mn at day 30. Later Egyptian astronomers refined this into a 25-year cycle of 309 lunar months — recorded in the Carlsberg 9 and Rylands IV 589 papyri — that kept the Moon and the 365-day civil year in step to within about an hour over 25 years. Iah is the lunar half of a sky also watched by Sun, decans, and stars; keep it distinct from Khonsu when an inscription means the Moon rather than the god.

Historical Origin

The lunar vocabulary built on iah is pan-Pharaonic, attested from the Old Kingdom onward; Belmonte and Lull treat jaH as foundational Egyptian Moon-terminology. The thirty-day lunar-feast list naming the Feast of the Moon (iah) at day 18 is preserved in Brugsch's table from the Ptolemaic-era temple inscriptions at Edfu and Dendera, translated by Marshall Clagett (*Ancient Egyptian Science* Vol II, Doc III.6, pp. 285-287). The 25-year/309-month cycle survives in Papyrus Carlsberg 9 and Rylands IV 589 (2nd c. CE) and is echoed in Ptolemy's *Almagest*.

Definition

In Tradition

In Practice

Historical Origin

Further Reading