The Greeks studied the results of the measurements of

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

by the explorer Pytheas who voyaged to Britain and beyond, as far as the Arctic Circle (observing the

midnight sun The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When the midnight sun is seen in the Arctic, ...

), in 325 BC. They used several methods to measure latitude, including the height of the Sun above the horizon at midday, measured using a gnōmōn (a word that originally meant an interpreter or judge); the length of the day at the summer solstice, and the elevation of the Sun at

winter solstice The winter solstice, also called the hibernal solstice, occurs when either of Earth's poles reaches its maximum tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern and Southern). For that hemisphere, the winter ...

. The Greek

Marinus of Tyre Marinus of Tyre ( grc-gre, Μαρῖνος ὁ Τύριος, ''Marînos ho Týrios''; 70–130) was a Greek geographer, cartographer and mathematician, who founded mathematical geography and provided the underpinnings of Claudius Ptolemy' ...

(AD 70–130) was the first to assign a latitude and longitude to every place on his maps. From the late 9th century CE, the Arabian Kamal was used in equatorial regions, to measure the height of Polaris above the horizon. This instrument could only be used in latitudes where Polaris is close to the horizon. The

mariner's astrolabe The mariner's astrolabe, also called sea astrolabe, was an inclinometer used to determine the latitude of a ship at sea by measuring the sun's noon altitude (declination) or the meridian altitude of a star of known declination. Not an astrolabe ...

which gives the angle of the Sun from the horizon at noon, or the angle of a known star at night, was used from around the 15th to the 17th century. The observation of the Sun instead of Polaris enabled the measurement of latitude in the Southern hemisphere but required the use of solar declination tables. One of the most famous tables, but certainly not the first one, was published in 1496 by the Castilian Jew Abraham Zacut, then exiled in

Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...

. The

backstaff The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the u ...

, which measures the length of a shadow, was used from the 16th century and saw iterative improvements such as the

Davis quadrant The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the u ...

. These were in use in parallel with the octant and early sextant; the sextant eventually displaced the others, and is still used to this day. The sextant was mentioned by

Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a " natural philosopher"), widely recognised as one of the grea ...

(1643–1727) in his unpublished writings, and first implemented about 1730 by

John Hadley John Hadley (16 April 1682 – 14 February 1744) was an English mathematician, and laid claim to the invention of the octant, two years after Thomas Godfrey claimed the same. Biography He was born in Bloomsbury, London the eldest son of ...

(1682–1744) and Thomas Godfrey (1704–1749).

References

{{Reflist History of navigation Ocean exploration

See also

References