περίγειον

Perígeion pairs the Greek preposition perí ('around, near, close to') with gē ('earth') to produce 'the near-earth point' — the precise complement of apógeion. The preposition perí is one of the workhorses of Greek scientific vocabulary: it names proximity, encirclement, and thoroughness. The same prefix builds periphery (the surrounding boundary), peristalsis (the encircling contraction of the gut), and periscope (seeing all around). In astronomy, it anchors the vocabulary of orbital nearness. Where apogee names the moment of maximum separation, perigee names the moment of maximum closeness — when the orbiting body is most strongly pulled by Earth's gravity, moves fastest in its orbit, and, in the case of the moon, subtends a visibly larger angle in the sky.

The practical consequences of perigee fascinated Greek astronomers precisely because they were measurable with the instruments available to them. Hipparchus in the 2nd century BCE observed that the moon's apparent diameter varies across its orbit — at perigee it appears larger, at apogee smaller. This variation, calculable through careful observation, was evidence that the moon's distance from Earth was not constant, and the explanation of that variation drove the development of Greek mathematical astronomy. The eccentric-circle model and the epicycle model were both attempts to account for the perigee-apogee variation while preserving the Greek assumption that all celestial motion was fundamentally circular.

The word passed through the same Arabic-Latin translation channel as apogee, becoming al-ḥaḍīḍ in Arabic ('the lowest point') and perigaeum in medieval Latin. Copernicus, Tycho Brahe, and Kepler all used the Latinized form; Kepler's demonstration that orbits are ellipses gave perigee a physical reality that Greek geometers had only approximated through their elaborate system of circles. In a Keplerian ellipse, perigee is the point where the orbiting body is closest to the occupied focus — the focus where Earth sits — and Kepler's second law directly connects this to orbital speed: bodies move fastest at perigee, slowest at apogee, sweeping equal areas in equal times.

The popular culture encounter with perigee comes through the 'supermoon.' When a full moon coincides with perigee, the moon appears up to 14 percent larger in diameter and 30 percent brighter than a full moon at apogee. The effect is real enough to photograph but subtle enough to require side-by-side comparison to appreciate without measurement. The term supermoon was coined by astrologer Richard Nolle in 1979 and popularized by social media in the 2010s; the astronomical term perigee remained accurate while supermoon became the crowd-drawing headline. The Greek word for the near-earth point quietly underlies every awestruck photograph of an apparently swollen moon rising above a city skyline.