|
|
TODAY'S WEATHER
April 10, 2000 By Capt. Eric Buck Have you ever thought about how you get from one place to another on land? I don't mean whether you walk, ride a bicycle, or ride in a car, but how you find your way from where you start to where you are going. On land, we have trails, paths, roads, signs, and other physical landmarks to help us navigate from point A to point B. On the ocean, once we get far enough out to sea, we lose all sight of land and its familiar landmarks. The ocean is trackless; it offers no obvious markers to guide us. Looking in one direction, the ocean is just as flat and uniform as looking in any other direction. How do we know what direction to go? Now another question: have you ever gazed up at the stars on a clear dark night? It is amazing how captivating it can be. Perhaps you wondered how many stars there are, and how far away they are. You will also have noticed that some stars are brighter than others, and that some groups of stars form obvious shapes in the sky. Are there any practical uses for these stars other than filling our minds with a sense of wonderment? As it turns out, humans have been gazing at the stars and other celestial bodies for thousands of years and recording information about how they move. Early on, seafarers used the stars as guideposts to steer by. As the motions of the stars gradually came to be understood, the art of celestial navigation was developed so that accurate positions could be determined at sea. In the last two centuries, marine navigation has progressed from art to science. Electronics and satellites have revolutionized navigation, and today we can instantly determine our position with incredible accuracy. It will be interesting to see what advances this new century will bring to the science. Despite all the electronic gadgets, one of the most satisfying activities for today’s navigators is to do things the old fashioned way; that is, to complete an ocean crossing navigating solely by the stars. On those clear, dark nights, the stars you’ve seen that are brighter than the rest are part of a select group of stars known as the Navigational Stars. The brightest stars are chosen for navigation because they are the easiest to identify and are easier to see in the twilight when most celestial observations are made. The sun, moon and planets can also be used for celestial navigation. The navigator finds his or her position by using a sextant to measure the altitudes (heights) of several stars above the horizon. These readings are compared to predicted altitudes and a line of position is plotted for each star. The intersection of the lines of position reveals your location. Many a seasoned navigator can get a rough idea of their whereabouts just by looking up and seeing what stars and constellations are visible and where they are in relation to the horizon. When Melville left San Diego in February, the Big Dipper, perhaps the best-known constellation in the northern hemisphere, was high in the sky. As we have worked our way southward, the Dipper is lower and lower in the northern sky. Our arrival in the tropics was confirmed by seeing the Southern Cross in the southern sky. How many constellations can you identify? Did you know that quite a few constellations have several navigational stars in them? If you’re interested in learning more about stars and constellations, check your library or local bookstore for H.A. Rey’s “The Stars, A New Way to See Them”. If you want more in-depth information, check out the “American Practical Navigator” by Nathaniel Bowditch, the book considered by many to be the bible of navigation. There is also a wealth of information on star-gazing and using stars and planets for navigation on the web. A visit to a planetarium or an observatory is another great way to learn about the stars. . Good star gazing!
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2010 Dive and Discover™. Dive and Discover™ is a registered trademark of
Woods
Hole Oceanographic Institution
