- How is exact position determined in degrees?
- Why is the equator represented as zero degrees?
The longitude of a place on earth was traditionally determined by measuring the time difference between two places, as the earth revolves 360 degrees in 24 hours, that gives 15 degrees longitude per hour time difference. Traditionally London is zero degrees Longitude, but in the past Paris and the Spanish island Hierro were also used as zero longitude.
The latitude is astronomically determined by the angle of the north polar star above the horizon. On the north pole that is 90 degrees, on the equator it is zero degrees. For the area south of the equator other stars were used.