# Clime

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 of longest daylight at summer solstice were used to calculate the changing length of daylight through the year.
The modern concept of climate and the related term clime are derived from the historical concept of climata.

## Ptolemy

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 in Arabo-Persian astronomy, by authors such as al-Biruni and al-Idrisi, and eventually by Amīn Rāzī, the author of the 16th-century haft iqlīm (lit. 'seven climes'), while in Europe, Aristotle's system of five climes 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.

### Thirty-nine parallels

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 between the equator and the polar circle (39 parallels between the equator and the pole) of the full system of climes; the reduced system of seven climes is indicated by additional numbers in brackets. Both Ptolemy's latitude estimates and modern values are provided. Ptolemy never considered the impact of atmospheric refraction on his calculation of the length of the day. If you account for that and for the drift in orbital parameters since Ptolemy's time, his values are remarkably accurate, off by less than 30 arcseconds in most cases.
| parallel | clima | Ptolemy's latitude | actual latitude | longest daylight | location |
| 1. | | 0° | 0° | 12 hours | (equator) |
| 2. | | 4°4' N | 2°14' N | 12:15 | Taprobana (Sri Lanka) |
| 3. | | 8°25' N | 6°31' N | 12:30 | Avalites (Saylac, Somalia) |
| 4. | | 12°00' N | 10°42' N | 12:45 | bay of Adulis (Eritrea) |
| 5. | I | 16°27' N | 14°46' N | 13:00 | Meroe island |
| 6. | | 20°14' N | 18°39' N | 13:15 | Napaton (Nubia) |
| 7. | II | 23°51' N | 22°20' N | 13:30 | Syene (Aswan) |
| 8. | | 27°12' N | 25°48' N | 13:45 | Thebes |
| 9. | III | 30°22' N | 29°3' N | 14:00 | Lower Egypt |
| 10. | | 33°18' N | 32°4' N | 14:15 | Phoenicia |
| 11. | IV | 36°00' N | 34°53' N | 14:30 | Rhodes |
| 12. | | 38°35' N | 37°29' N | 14:45 | Smyrna |
| 13. | V | 40°56' N | 39°53' N | 15:00 | Hellespont |
| 14. | | 43°04' N | 42°5' N | 15:15 | Massalia (Marseilles) |
| 15. | VI | 45°01' N | 44°7' N | 15:30 | the middle of the Euxine Sea |
| 16. | | 46°51' N | 45°59' N | 15:45 | Istros (Danube) |
| 17. | VII | 48°32' N | 47°43' N | 16:00 | the mouths of Borysthenes (Dnepr) |
| 18. | | 50°04' N | 49°18' N | 16:15 | Maeotian Lake (Sea of Azov) |
| 19. | | 51°06' N | 50°45' N | 16:30 | the southern shore of Britannia |
| 20. | | 52°50' N | 52°6' N | 16:45 | mouths of the Rhine |
| 21. | | 54°1' N | 53°20' N | 17:00 | mouths of the Tanais river (Don) |
| 22. | | 55° N | 54°29' N | 17:15 | Brigantion in Britannia |
| 23. | | 56° N | 55°32' N | 17:30 | the middle of Great Britain |
| 24. | | 57° N | 56°30' N | 17:45 | Katouraktonion in Britannia |
| 25. | | 58° N | 57°24' N | 18:00 | the southern part of Britannia Minor |
| 26. | | 59° N | 59°0' N | 18:30 | the middle part of Britannia Minor |
| 27. | | 61° N | 60°21' N | 19:00 | the northern part of Britannia Minor |
| 28. | | 62° N | 61°30' N | 19:30 | Ebudes island |
| 29. | | 63° N | 62°29' N | 20 hours | Thule |
| 30. | | 64°30' N | 63°59' N | 21 hours | unknown Scythians |
| 31. | | 65°30' N | 64°59' N | 22 hours | |
| 32. | | 66° N | 65°33' N | 23 hours | |
| 33. | | 66°8'40"N | 65°44' N | 24 hours | polar circle |
| | | 69°30' N | 68°48' N | 2 months | |
| | | 78°20' N | 77°27' N | 4 months | |
| 39. | | 90° N | 90° N | 6 months | (North Pole) |