Roger Morris, age 15, of Orlando, Fla., for his question:
CAN YOU EXPLAIN NAVIGATION?
Navigation is the science of finding your location and the direction of your course while you are sailing a ship at sea. When referring to airplanes, "air navigation" is the term used.
If you are within sight of land, piloting of the craft is done visually by finding landmarks such as lighthouses and buoys. Electronic aids such as radar and a radio direction tinder are used for piloting if there is fog.
The compass, either magnetic or gyrocompass, is an important instrument used in piloting. It is used in steering and in finding directions.
A radio direction finder is used to take bearings of radio beacons. The bearings of two or more radio beacons are plotted by drawing lines on a chart. The navigator knows his ship is located where the lines cross.
A Fathometer measures the depth of the water.
Radar is used when darkness or fog made it hard for the navigator to see. Radar shows him what objects are near.
Charts provide most of the information needed for piloting. They show water depths and locations of such aids to navigation as buoys and beacons. Charts also show the exact locations of rocks, coastlines, shoals and islands. They also show anchorage areas and ship channels.
Celestial navigation is navigation by the sun or stars. It is used when the craft is out of sight of land.
The sextant and chronometer are the chief instruments used in celestial navigation. The sextant measures the altitude of the sun, planet or star. The chronometer is an accurate clock set to show the time at Greenwich, London, which is longitude zero.
Electronic navigation devices include radar, the echo sounder, sonar (sound navigation and ranging), Shoran (short range navigation) Loran (long range navigation) and sins (ships inertial navigational system).
In air navigation, altimeters and air speed indicators are also used.
Information as to the positions of heavenly bodies is provided by the U.S. Naval Observatory. The navigator uses his sextant to find the angle above the horizon of three heavenly bodies. The readings are written down along with the exact time they were taken. With this information, the navigator can tell his location almost exactly.
Navigational radio sends out a beam of electromagnetic waves. The waves hit an object and send back echoes that show as "pips" on the screen of a cathode ray tube. The distance of the object and its direction can then easily be measured.
Radar beacons, "racon" for aviators and "ramark" for mariners, transmit signals in code when they are activated by a signal from radar.
The navigator uses an echo sounder to measure the time interval between the sound and the return of the echo from the bottom of the sea. From this he can figure out the water depth.