Welcome to You Ask Andy

Robert Marlan, age 9, of Rochester, New York, for his question:

How does a pilot navigate at night?

A plane pilot is too far up to read road signs, day or night. Out on the ocean, one wave looks just like the others, and none of them are marked with signs. But the pilots of planes and ships have other ways to navigate. Some of these tricks are very old and others were invented in the space age.

Directions on the ground are plotted. from the earth's North Pole. Facing north, of course, the east is on your right side, the west on your left, and the south direction is behind you. Road maps are charted on these basic directions, and you might think that pilots would get lost without them. Not at all. Our ground directions were not discovered and plotted on the ground. We do not have to march to the North Pole to check the north direction    all we need do is look up and find the North Star in the sky. This star, of course, is always there to point out the north direction to pilots and lonely travelers far from home.

This gives you a clue. At night a pilot can guide his ship or plane from the North Star in the sky. He carries a compass and a special clock, a gadget to check his mileage and lots of charts. With these helpers, he can also use many other stars as markers to guide him on his way. This direction finding by the heavens is called celestial naviga¬tion. A pilot must learn the tricks to make it work. But the trouble is worth it. Celestial navigation tell more than where he is and where to go. It can also tell him the exact time of the day or night.

A modern pilot has other gadgets to guide him when the sun and stars are hidden by clouds. Large airports beam out powerful radio signals. Some lighthouses and light ships also send out radio beams. These signals travel in perfectly straight lines, and day or night, a pilot can follow them and let them guide him straight home. He also has a gadget to show him how fast he is traveling, and another to show how high he is above the ground. Radio beams and these gadgets are guides to navigation day or night, through cloudy skies or sunny skies.

A pilot keeps very accurate records of how fast he has been traveling and in what direction, and he can use this information to determine his exact location at any moment. This system is called "dead reckoning," and it can save ships, planes and lives. Actually, the "dead" should be spelled "ded," because it is short for the word "deduced." A pilot uses a lot of clues, tricky figuring and reckoning and comes to his answer by a process of deduction. This clever dead reckoning can be used to navigate at night, even when land¬marks and sky pointers are out of sight.

A pilot can use dead reckoning to find just where he is on the sea or in the sky above the earth. His maps and charts show the right direction to take and the distance to his destination. A compass or the North Star can point out the direction. A mileage gauge checks off the distance as he travels his course. The earth's lines of longitude are plotted from points in the sky. And longitude tells the time of day. When a pilot knows where he is, he may check the sun or the stars above him. He then can use a special alma¬nac to tell him the time of day or night.T

Today we have satellites in orbit named Global Positioning Satellies that are  used to precisely determine the position of a plane in the air, a car or a person on the ground.


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