Glyph and Origin

Its glyph resembles a numeral four or a stylised Greek letter, sometimes traced to the initial of Zeus. Jupiter is one of the seven classical planets of ancient Mesopotamian and Hellenistic astrology. The zeta-with-stroke reading is visible in the same run of late Greek papyri and Byzantine astrological manuscripts that preserve the other classical glyphs, and a diagram in the twelfth-century astronomical compendium of the Byzantine writer Johannes Kamateros still shows Jupiter marked with a recognisable zeta, evidence that the abbreviation had already worn down toward its modern, more schematic four-like shape by the high medieval period without losing its Greek letterform underneath.

Jupiter's sign entered the Unicode standard together with the rest of the classical planetary set in the Miscellaneous Symbols block of its 1991 release, fixing a form whose journey from a labelled Greek letter to an unlabelled numeral-like mark had already taken the better part of two thousand years by the time computer typography inherited it. That long wearing-down is typical of the classical planetary signs generally, each of which began as a legible abbreviation of a god's name in Greek and only gradually lost enough detail, through centuries of hurried copying by scribes who no longer needed to spell out what a symbol they used constantly already meant, to look like the more abstract marks now printed in modern astrological texts.