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By the stars they are guided

Surah al-Nahl mentions landmarks, and adds that by the stars they are guided. This was a working technology, not a figure of speech. The altitude of the pole star above the horizon equals your latitude, so a sailor who can measure that angle knows how far north he is. Indian Ocean pilots did it with the kamal, a small wooden plate on a knotted string held at arm's length, one knot per port. Ahmad ibn Majid, a pilot from Julfar who wrote navigation manuals in the fifteenth century, set out star bearings and courses in verse so that crews could memorise them. The sextant refined the same measurement, and warships still teach it in case the satellites go dark.

Surah al-Nahl 16:16

Source · Qur'an 16:16