Navigation and Seamanship

1.2.9. Longitude

                                                                        

           Longitude (l, long.) is the angular distance between the prime meridian and the meridian of a point on the earth, measured eastward or westward from the prime meridian through 180°. It is designated east (E) or west (W) to indicate the direction of measurement. The prime meridian, longitude 000°, is universally taken as the meridian which passes through the original site of the Royal Observatory, Greenwich, England. All modern charts use the prime meridian as the starting point for the measurement of longitude.