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<li class="leaf"><a href="/navigating-air" title="">Navigating in the Air</a></li>
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<li class="leaf"><a href="/satellite-navigation" title="">Satellite Navigation</a></li>
<li class="leaf"><a href="/navigation-for-everyone" title="">Navigation for Everyone</a></li>
<li class="leaf"><a href="/timeline" title="">Timeline of Innovation</a></li>
<li class="leaf"><a href="/artifacts" title="">Artifacts</a></li>
<li class="leaf"><a href="/learning-resources" title="">Learning Resources</a></li>
<li class="leaf"><a href="/multimedia-gallery" title="">Multimedia Gallery</a></li>
<li class="leaf"><a href="/research" title="">Research Journal</a></li>
<li class="last leaf"><a href="/visit-the-exhibition" title="">Visit the Exhibition</a></li>
</ul> </div>
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<ul class="menu"><li class="first expanded menu-mlid-526"><a href="/navigating-at-sea/challenges" title="Challenges of Sea Navigation link">Challenges of Sea Navigation</a><ul class="menu"><li class="first leaf menu-mlid-1069"><a href="/navigating-at-sea/challenges/british-fleet-runs-aground" title="A British fleet is lost at sea.">Navigation Gone Wrong: A British Fleet is Lost at Sea</a></li>
<li class="last leaf active menu-mlid-527"><a href="/navigating-at-sea/challenges/navigate-the-sea-activity" title="Use a sextant and chronometer to keep yourself on course. And hurry! You want to beat the record of the clipper ship Flying Cloud!" class="active">Navigate at Sea! Activity</a></li>
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<li class="expanded menu-mlid-528"><a href="/navigating-at-sea/navigating-without-a-clock" title="Navigating without a Clock link">Navigating Without a Clock</a><ul class="menu"><li class="first leaf menu-mlid-1070"><a href="/navigating-at-sea/navigating-without-a-clock/early-voyages" title="People accomplished amazing feats of navigation well before Europeans took to the seas.">Early Voyages</a></li>
<li class="leaf menu-mlid-1072"><a href="/navigating-at-sea/navigating-without-a-clock/dead-reckoning" title="Simple navigation methods and instruments served mariners for centuries.">Dead Reckoning</a></li>
<li class="last leaf menu-mlid-1073"><a href="/navigating-at-sea/navigating-without-a-clock/celestial-navigation" title="Navigators began using special instruments to find latitude at sea.">Celestial Navigation</a></li>
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<li class="expanded menu-mlid-529"><a href="/navigating-at-sea/longitude-problem" title="The Longitude Problem link">The Longitude Problem</a><ul class="menu"><li class="first leaf menu-mlid-1074"><a href="/navigating-at-sea/longitude-problem/cash-for-creativity" title="European governments offered huge prizes to solve the longitude problem.">Cash for Creativity</a></li>
<li class="leaf menu-mlid-1076"><a href="/navigating-at-sea/longitude-problem/solving-longitude-problem/early-sea-clocks" title="Finding longitude greatly improved once a portable clock was invented.">Early Sea Clock Experiments</a></li>
<li class="leaf menu-mlid-1077"><a href="/navigating-at-sea/longitude-problem/solving-longitude-problem/innovation-in-england" title="Clockmaker John Harrison demonstrates a workable timepiece for finding longitude at sea.">Innovations in England</a></li>
<li class="leaf menu-mlid-1078"><a href="/navigating-at-sea/longitude-problem/solving-longitude-problem/innovation-in-france" title="Finding longitude on land and at sea was a major preoccupation in France.">Innovations in France</a></li>
<li class="leaf menu-mlid-1079"><a href="/navigating-at-sea/longitude-problem/solving-longitude-problem/chronometer" title="To design and build a standardized seagoing timekeeper took decades.">The Chronometer</a></li>
<li class="leaf menu-mlid-1080"><a href="/navigating-at-sea/longitude-problem/observing-the-skies" title="Finding longitude greatly improved once better angle-measuring instruments and star charts were available.">Observing the Skies</a></li>
<li class="last leaf menu-mlid-1081"><a href="/navigating-at-sea/longitude-problem/wreck-of-the-arniston" title="Sailing without a chronometer proved deadly.">Navigation Gone Wrong: Wreck of the Arniston</a></li>
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<li class="expanded menu-mlid-1082"><a href="/navigating-at-sea/us-goes-to-sea" title="The U.S. Goes to Sea link">The U.S. Goes to Sea</a><ul class="menu"><li class="first expanded menu-mlid-1083"><a href="/navigating-at-sea/us-goes-to-sea/early-contributions" title="America’s earliest contributions to navigation aimed to lessen the dangers of seafaring.">Early Contributions</a><ul class="menu"><li class="first leaf menu-mlid-1085"><a href="/navigating-at-sea/us-goes-to-sea/early-contributions/meet-the-clockmaker" title="The firm of William Bond & Son became one of America’s best known chronometer dealers.">Meet the Clockmaker: William Cranch Bond</a></li>
<li class="last leaf menu-mlid-1086"><a href="/navigating-at-sea/us-goes-to-sea/early-contributions/meet-the-navigator" title="The wife of the Flying Cloud’s master was the ship’s navigator.">Meet the Navigator: Eleanor Creesy</a></li>
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<li class="last expanded menu-mlid-1087"><a href="/navigating-at-sea/us-goes-to-sea/wilkes-expedition" title="The United States dispatched an ambitious mission to uncharted oceans.">Wilkes Expedition</a><ul class="menu"><li class="first leaf menu-mlid-1088"><a href="/navigating-at-sea/us-goes-to-sea/wilkes-expedition/meet-the-mapmaker" title="Captain Charles Wilkes became known for his expertise and accuracy in mapping and charting.">Meet the Mapmaker: Charles Wilkes</a></li>
<li class="leaf menu-mlid-1089"><a href="/navigating-at-sea/us-goes-to-sea/wilkes-expedition/maps-charts" title="In four years, the expedition effectively remapped the Pacific Ocean.">Maps and Charts</a></li>
<li class="last leaf menu-mlid-1090"><a href="/navigating-at-sea/us-goes-to-sea/wilkes-expedition/scientifics" title="The expedition also included a formidable group of botanists, naturalists, artists, taxidermists, and other scientists.">The "Scientifics"</a></li>
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<li class="last leaf active-trail active menu-mlid-1276"><a href="/navigating-at-sea/challenges/navigate-the-sea-activity" title="Use a sextant and chronometer to keep yourself on course. And hurry! You want to beat the record of the clipper ship Flying Cloud!" class="active-trail active">Navigate at Sea! Activity</a></li>
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<h1>Navigate at Sea! Activity</h1>
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<div class="label1 text fade abs">Navigators have long used reliable clocks and the stars to find their position at sea. Come aboard and try your hand at celestial navigation.</div>
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<div class="label1 text fade abs">A star's position in the sky changes depending on the time and your location.</div>
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<div id="angle330" class="item item-first">3:30</div>
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<div id="angle430" class="item">4:30</div>
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<img id="image345" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/angles/angle345.jpg" alt="" />
<img id="image400" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/angles/angle400.jpg" alt="" />
<img id="image415" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/angles/angle415.jpg" alt="" />
<img id="image430" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/angles/angle430.jpg" alt="" />
<img id="image445" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/angles/angle445.jpg" alt="" />
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<div class="label1 text fade abs">You can use a sextant to measure a star's position above the horizon. Adjust the sextant until you see the star line up with the horizon.</div>
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<div class="label3 text small fade abs">Horizon</div>
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<div id="deg0" class="item item-first">0 degrees</div>
<div id="deg10" class="item">10 degrees</div>
<div id="deg15" class="item">15 degrees</div>
<div id="deg20" class="item">20 degrees</div>
<div id="deg25" class="item">25 degrees</div>
<div id="deg30" class="item">30 degrees</div>
<div id="deg35" class="item">35 degrees</div>
<div id="deg40" class="item">40 degrees</div>
<div id="deg45" class="item">45 degrees</div>
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<img id="image15" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/degrees/deg15.jpg" alt="" />
<img id="image20" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/degrees/deg20.jpg" alt="" />
<img id="image25" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/degrees/deg25.jpg" alt="" />
<img id="image30" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/degrees/deg30.jpg" alt="" />
<img id="image35" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/degrees/deg35.jpg" alt="" />
<img id="image40" class="image" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/degrees/deg40.jpg" alt="" />
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<div class="label1 text fade abs">There are other places on Earth where the star would be at the same angle at the same time.</div>
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<div class="label1 text fade abs">Using a mathematical table, we can calculate where all these possible positions would be. They would form a circle on the Earth.</div>
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<div class="label1 text fade abs">When we look closely, this forms a line called a "Line of Position."<br /><br />Your ship is somewhere on this line.</div>
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<button class="restart fade abs"><img src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/buttons/restart_btn_up.png" alt="Restart" /></button>
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<div class="label1 text fade abs">To find where you are, you need to measure a second star, and find where these two lines of position intersect.</div>
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<img class="title1" src="http://timeandnavigation.si.edu/sites/all/themes/timeandnav/interactives/modules/sea/images/labels/let_me_do_it_label.png" alt="Let Me Do It!" />
<div class="text">I'm up for the challenge.</div>
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<div class="text">No thanks. Do it for me.</div>
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<div class="text abs text1">First let's sight the star. Which measurement best suits the angle between the horizon and the bright star?<br /><br /><em>Select the correct angle.</em></div>
<div class="text abs none text2">The star is 15 degrees above the horizon.</div>
<div class="label1 abs">Star</div>
<div class="label2 abs">Horizon</div>
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<div id="deg5mini" class="item">5 degrees</div>
<div id="deg15mini" class="item">15 degrees</div>
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<div class="text abs text1">Now, observe the chronometer. Which time is closest to the time displayed?<br /><br /><em>Select the correct time.</em></div>
<div class="text abs none text2">The correct time is:</div>
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<button id="clock405">4:05:30</button>
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<div class="text abs">Knowing the time and altitude of the star, we can find the data needed to calculate the ship's line of position.</div>
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<div class="label1 text fade abs">You found the correct location to your ship!</div>
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<div class="label1 text fade abs">You need to have very accurate measurements for celestial navigation.</div>
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