A north-south line is called a meridian or longitude. Meridians are measurements of width and give the angle between the Greenwich meridian and any other place. The longitude is the angular distance (east-west) from the standard meridian. If we say that the longitude of Pretoria is 28° 15' E, we mean that Pretoria lies on a meridian 28° 15' east of the Greenwich meridian.

If it is noon at one place on a specific meridian it will also be noon at all other places on the same meridian.

  The nautical mile is defined as 1 minute of latitude and since the earth is not a perfect sphere the nautical mile is shorter at the equator than at the north or south pole.
An international nautical mile = 1,852 km.

The earth is divided into 24 time zones and therefore
1 hour = 15 °. View a World Time Zone Map.

More about longitude and the naviagtion problems 17th century sailors had can be found at on the Royal Observatory web pages under The Longitude Problem.

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© Helga Nordhoff (2001-2008)