Clim(at)e (more correctly klima or clima, plur. klimata and climata, from Greek κλίμα/κλίματα) is a concept of referring to the angle between the axis of the celestial sphere and the horizon, and the terrestrial latitude characterized by this angle. In most cases, it can safely be translated as “latitude”. Normally, klimata were defined by the length of the longest daylight and associated with specific geographical locations. Different lists of klimata 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 klimata (Almagest 2.12) which, due to his authority, became one of the canonical elements of late antique, medieval European and Arab geography.
Klimata should not be confused with climatic (in modern sense) zones. Traditionally, 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.
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).
Ptolemy's system of seven climes was primarily adopted by Arab and Persian authors such as al-Biruni, al-Idrisi and al-Razi, the author of the 16th century haft iqlīm (seven climes), while in Europe, Aristotle's system of five zones was more successful. This view dominated in medieval Europe, and existence and inhabitability of the Southern temperate zone, the antipodes, was a matter of dispute.
To identify the parallels delineating his climes, Ptolemy gives a geographical location through which they pass. The following is a list of the 33 parallels of the full system of climes, the reduced system of seven climes is indicated by additional numbers in brackets (note that the latitudes are the ones given by Ptolemy, not the modern exact values):
- 12:00 (equator)
- 12:15, 4°4' N: Taprobana (Sri Lanka)
- 12:30, 8°25' N: Avalite bay (Saylac, Somalia)
- 12:45 12°00' N: bay of Adulis (Eritrea)
- (1.) 13:00, 16°27' N: Meroe island
- 13:15, 20°14' N: Napaton (Sudan)
- (2.) 13:30, 23°51' N: Soene (Aswan)
- 13:45, 27°12' N: Thebes
- (3.) 14:00, 30°22' N: Lower Egypt
- 14:15, 33°18' N: Phoenicia
- (4.) 14:30, 36°00' N: Rhodes
- 14:45, 38°35' N: Smyrna
- (5.) 15:00, 40°50' N: Hellespont
- 15:15, 43°04' N: Massalia (Marseilles)
- (6.) 15:30, 45°01' N: the middle of the Black Sea
- 15:45, 46°51' N: Istros river
- (7.) 16:00, 48°32' N: the mouths of Borysthenes (Dnepr)
- 16:15, 50°04' N: Maeotian Lake (Sea of Azov)
- 16:30, 51°06' N: the southern shore of Britannia
- 16:45, 52°50' N: mouths of the Rhine
- 17:00, 54°30' N: mouths of the Tanais river (Don)
- 17:15, 55° N: Brigantion in Britannia
- 17:30, 56° N: the middle of Great Britain
- 17:45, 57° N: Katouraktonion in Britannia
- 18:00, 58° N: the southern part of Britannia Minor
- 18:30, 59° N: the middle part of Britannia Minor
- 19:00, 61° N: the North of Britannia Minor
- 19:30, 62° N: Ebudes island
- 20:00, 63° N: Thule (Iceland)
- 21:00, 64° N: unknown "Scythian people"[?]
- 22:00, 65° N
- 23:00, 66° N
- 24:00, 66°08'40'' N: the polar circle
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