The stars in this constellation are never visible in the Northern Hemisphere above the tropics. The most familiar constellation in the Southern Hemisphere, for instance, is the Southern Cross. Navigators must be familiar with the different constellations at different times of the year, as well as the different constellations in the Northern and Southern Hemispheres. It is very useful on the open ocean, where there are no landmarks. This technique uses the stars, moon, sun, and horizon to calculate position. Celestial Navigation For sailors, celestial navigation is a step up from dead reckoning. This can make it difficult to realize when mistakes are made during travel. However, the only reference point in dead reckoning is the past position. When used in sailing, it does not take into account wind speeds or ocean currents. Dead reckoning factors in speed, time, and direction of travel. Dead Reckoning Dead reckoning involves estimating a current position based on a past position. Compasses were being used for navigation by the 1100s C.E., and are still the most familiar navigational tools in the world. Compasses, which indicate direction relative to the Earth's magnetic poles, are used in navigation on land, at sea, and in the air. The ancient Minoans, who lived on the Mediterranean island of Crete from 3000 to 1100 B.C.E, left records of using the stars to navigate, for instance. When that was impossible, ancient sailors watched constellations to mark their position. Instead, they sailed within sight of land in order to navigate. Few ancient sailors ventured out into the open sea. The earliest navigation methods involved observing landmarks or watching the direction of the sun and stars. People have been using some of them for thousands of years. There are many different navigation techniques. Latitude is a north-south position measured from Earth's Equator and longitude is an east-west position measured from the prime meridian. Understanding latitude and longitude are very important in navigation. Navigators measure distance on the globe in degrees. Navigation requires a person to know the vehicle's relative location, or position compared to other known locations. Navigation is the art and science of determining the position of a ship, plane or other vehicle, and guiding it to a specific destination.
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