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Circles parallel to the equator, ranging from 0° to 90° N or S. Only the equator is a great circle. 


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halfcircles converging at the poles, ranging from 0° to 180° E or W. Each pair of opposing meridians forms a great circle. 


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0° or the Greenwich meridian which  together with the date line meridian  divides the Western and Eastern hemispheres. 


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The intersection of a sphere and a plane that passes through the sphere's centre. 


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The intersection of a sphere and a plane that doesn't pass though the sphere's centre. 


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By convention 24 zones, each 15° longitude wide. Hence, noon at Greenwich gives midnight at 180° E. 


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The 180° meridian which extends from or is opposite to the prime meridian. Here, not only the hour changes when crossing the meridian, but also the date. 


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Position property defined by the number of degrees north or south of the equator, varies from 0° to 90°. 


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Position property defined by the number of degrees east or west of the prime meridian, varies from 0° to 180°. 


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Latitude first and longitude second. For example: Athens in Greece 37° 58' N , 23° 43' E. 


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One nm is one minute (') on the vertical scale on the chart. 1' equals 1852 metres. Nautical miles are divided into 10 cables. 


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It takes the earth 24 hours for a full rotation of 360°. Thus, every hour we rotate __° longitude 

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The North Pole has a latitude of __° N 

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