Longitude

lon'ji-tud, the measure of length. In geography, it is the angular distance on the earth's surface east or west of a north and south line called the first or prime meridian. English-speaking people reckon longitude from a north and south line passing from pole to pole through the Royal Observatory of Greenwich, near London. It is quite customary to reckon longitude from the capital of the nation. Formerly American maps were based on the meridian of Washington; French maps are still based on the meridian of Paris; but there is a tendency to adopt the meridian of Greenwich as being in most general use. The equatorial distance around the earth is divided into 360 parts called degrees. A degree of longitude on the equator is 69.1 statute miles in length. As the meridians come nearer together as they approach the poles, the farther north a degree is measured the shorter it is. At the poles the value of a degree of longitude is zero. On the forty-ninth parallel, the boundary between the United States and Canada, the value of a degree is 45.8 miles. Longitude is reckoned as east or west from the prime meridian. The 180th meridian may be considered either east or west. A difference of fifteen degrees in longitude is equivalent to an hour's difference in time. See Standard Time; International Date Line, etc.