Eta η

Eta is the seventh letter of the Greek alphabet, from Phoenician heth; its value is 8. In classical Greek it marked a long 'e'. Eta has no significant independent esoteric tradition; its interest is linguistic and, through isopsephy, numerical. The Greek letters doubled as numerals in the Milesian (alphabetic) system, in which each letter carried a fixed value; the practice of summing a word's letters into a number, called isopsephy, is the Greek counterpart of Hebrew gematria and appears in inscriptions, the Greek Magical Papyri and early Christian texts. Eta's Phoenician ancestry places it in a borrowing whose exact point of contact, somewhere among Al Mina, Cyprus, Crete and Euboea in the Aegean world, is still disputed, though the borrowing itself, conventionally dated to around the 8th century BCE, is agreed to be the ancestor of every European alphabet still in use, including the Latin one covered elsewhere in this atlas.

The Greeks' own contribution was to give vowels dedicated letters of their own, something the consonant-only Phoenician script never did. Its isopsephy value of 8 belongs to the Milesian alphabetic numeral system, which also needed three further, otherwise obsolete letters, digamma (also called stigma), koppa and sampi, to cover every value from 1 up to 900; none of the three survives among the 24 letters in ordinary use today.

Eta's presence in the Greek alphabet used today is itself a piece of script history distinct from the letter's ancient sound and number, covered elsewhere in this atlas. Archaic Athens used its own local, or epichoric, alphabet, which had no separate sign for a long e sound and simply wrote both long and short e with epsilon; the Ionic alphabet of Miletus, by contrast, had already repurposed an old consonant letter, eta, originally standing for the sound h in many other Greek dialects, to mark the long vowel instead. When Athens formally adopted the Ionic alphabet by decree in 403 BCE, under the archon Eucleides, eta's consonant value was dropped in Athenian and most subsequent Greek entirely, and the letter became purely the long-e vowel still used in modern Greek; the h sound it once carried survives today only in the rough breathing mark placed over vowels in polytonic Greek spelling.

Modern technical use of eta is comparatively minor: physicists and engineers use lowercase eta for efficiency ratios and for the viscosity of a fluid, and astronomers, following the Bayer star-naming convention of 1603, use Eta to mark a constellation's seventh-brightest star. The letter's two-stage history, an old consonant repurposed as a vowel through a specific, dated political decision, has no real parallel among the Latin letters covered elsewhere in this atlas, whose shape changes were generally gradual rather than decreed.