导航

导航(navigation)

导引交通工具，确定位置、路线与前进距离的科学。早期的船员注视着岸边可见的地标并研究主要的风向作为方向的指引。腓尼基人和玻里尼西亚人航行超出陆地的视线，利用恒星来校正路线。罗盘（中国人於西元1100年左右最早使用）是第一种导航的辅助工具，当成固定的参考点，不过精度有限，特别是在波涛汹涌的海面。现代的罗盘由陀螺仪加以稳定，放在补偿船舰颠簸效应的罗盘柜内。船的速度最早的计算方法是往船外丢上一节木头，上面绑着一捆绳子，每隔固定的间距打个绳结；当木头漂浮而暴露在外绳结数目，加上沙漏的时间，就得到船的速度，称为节（每小时海里）。航海图是另一项必备的导航工具。定位需要航海图上详细的已知位置、加上仪器计算相对於这些点的方位。早期测定纬度的仪器是象限仪，测量北极星或正午太阳的高度。另外的早期仪器还有六分仪和星盘。确定纬度（在17至18世纪逐渐成功地用於导航）是利用时计以及显示全年天体位置的表格。在20世纪，无线电信标台与卫星网路让飞机和船舰确定其位置。航迹是从陀螺仪得到航向，从电脑化量测船的加速度得到速率，将整个精确历程绘制而成。亦请参阅Global Positioning System。

English version：

navigation

Science of directing a craft by determining its position, course, and distance traveled. Early mariners followed landmarks visible on shore and studied prevailing winds for clues to direction. The Phoenicians and Polynesians sailed out of sight of land and used the stars to set their course. The compass (first used by the Chinese c. 1100) was the first navigational aid that gave a constant reference point, though its accuracy was limited, especially in heavy seas. Modern compasses are stabilized by gyroscopes and housed in binnacles that compensate for the craft's motion. Ship speed was first calculated by dropping overboard a log attached to a reel of line knotted at regular intervals; the number of knots exposed while the log drifted and a sandglass emptied gave the vessel's speed in knots (nautical mph). Charts are another essential navigational tool. Fixing a position requires charts detailing known locations, together with instruments that calculate a vessel's bearing relative to them. The earliest instrument for determining latitude was the quadrant, which measured the altitude of the polestar or the noonday sun. Other early instruments included the sextant and the astrolabe. Longitude (used for navigation with increasing success in the 17th-18th century) was fixed using chronometers and tables showing positions of celestial bodies throughout the year. In the 20th century, radio beacons and satellite networks allowed aircraft and ships to determine their position. Dead reckoning uses an accurate history of a vessel's headings and speeds drawn from gyroscopes and from computerized measurements of the craft's acceleration. See also Global Positioning System.