Seven climes

The climes (singular clime; also clima, plural climata, from Greek κλίμα klima, plural κλίματα klimata, meaning "inclination" or "slope") in classical Greco-Roman geography and astronomy were the divisions of the inhabited portion of the spherical Earth by geographic latitude.

Starting with Aristotle (Meteorology 2.5,362a32), the Earth was divided into five zones, assuming two frigid climes (the arctic and antarctic) around the poles, an uninhabitable torrid clime near the equator, and two temperate climes between the frigid and the torrid ones. Different lists of climata were in use in Hellenistic and Roman time. Claudius Ptolemy was the first ancient scientist known to have devised the so-called system of seven climes (Almagest 2.12) which, due to his authority, became one of the canonical elements of late antique, medieval European and Arab geography. In Medieval Europe, the climes for 15 and 18 hours were used to calculate the changing length of daylight through the year.

The modern concept of climate and the related term are derived from the historical concept of climata.

Ptolemy gives a list of parallels, starting with the equator, and proceeding north at intervals, chosen so that the longest day (summer solstice) increases in steps of a quarter of an hour from 12 hours at the equator to 18 hours at 58° N, and then, in larger steps, to 24 hours at the arctic circle.

But for the purposes of his geographical tables, Ptolemy reduces this list to eleven parallels, dividing the area between the equator and 54°1' N into ten segments, at half-hour intervals reaching from 12 hours to 17 hours. Even later in his work, he reduces this to seven parallels, reaching from 16°27' N (13 hours) to 48°32' N (16 hours).

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