The search for longitude

THE SEARCH FOR LONGITUDE

AT THE BEGINNING OF THE AGE OF EXPLORATION:

• People knew about lines of latitude and lines of longitude. But the only one that could be measured at sea was LATITUDE

• (AND THAT WAS VERY DIFFICULT)

TO FIND LATITUDE AT SEA, NAVIGATORS USED AN ASTROLABE ADAPTED TO MARINE USE

The angle between the North Star and the Horizon provided Latitude

LATER EXPLORERS USED A QUADRANT WHICH WAS EASIER TO USE ON A PITCHING AND ROLLING SHIP ON THE OCEAN

BUT TO FIND LONGITUDE, ONE HAD TO DO THE FOLLOWING:• Make several star sights or sun sights to accurately determine the time• Compare that with a place of known time(difficult to do when clocks weren’t

accurate)• Complete about 5 hours of math• This was impossible on a ship b/c it kept moving during the 5 hours you were

doing calculations.

ENTER THE LUNAR DISTANCE METHOD

ALL THAT WAS NEEDED WAS A CONVERSION TABLE TO INTERPRET THE MOON’S POSITION INTO LONGITUDE

However they weren’t very accurateAs it took 18 years of observations of The moon to accurately predict it’s orbit

EVERYONE KNEW THAT IF YOU HAD AN ACCURATE CLOCK, FIGURING LONGITUDE WOULD BE EASY:• The Earth rotates 360 degrees every 24 hours• Every hour the earth rotates 15 degrees• If you had a clock set to the time at the port you had just left and local time

on the ocean was 1 hour later than that time you were 15 degrees west of the home port

• However no clocks at that time were accurate enough

REASONS CLOCKS WERE NOT ACCURATE ON THE OCEAN:

• Temperature changes • Humidity changes• The motion of the ship

ENTER CLOCKMAKER JOHN HARRISON

• He made a clock that was accurate to use at sea. It wasn’t super accurate but it was better than what they had. Plus it was huge.

THE NEXT CLOCK WAS SMALLER, BUT STILL NOT ACCURATE ENOUGH

FINALLY HE MAKES ONE SIMILAR IN SIZE TO A POCKET WATCH

This watch was accurate enough to handle a rough Ocean voyage and was very accurate. With this watchNavigators always knew what time it was in their homePort and used the sun or stars to determine local time.The difference in time easily told what the longitude was

SO WHAT DOES THIS HAVE TO DO WITH US?

The GPS in our phones, cars, boats, and planes determineOur position by comparing what time it is in the receiver in ourDevice and what time it is in the satellite We are basically using an atomic clock version of John Harrison’s H4 Watch

WORKS CITED:• "Ancient Map with Longitude Only - Google Search." Ancient Map with Longitude Only - Google Search. Web. 12 Nov. 2014.

• Baudin, Michael. "John Harrison H4 Clock." Michel Baudins Blog. Web. 12 Nov. 2014.

• "The Collection." H1. Royal Museum Greenwhich Collection. Web. 12 Nov. 2014.

• "The Earth's Grid System." -- Kids Encyclopedia. Web. 12 Nov. 2014.

• "The Lunar Distance Method." National Museum of Australia -. Web. 12 Nov. 2014.

• "Map with Lines of Latitude Labeled - Google Search." Map with Lines of Latitude Labeled - Google Search. Web. 12 Nov. 2014.

• "Mariner's Astrolabe." Academic Dictionaries and Encyclopedias. Web. 12 Nov. 2014.

• Pickering, Keith A. "Columbus and Celestial Navigation." Columbus and Celestial Navigation. Web. 12 Nov. 2014. copyright 1997-2010

• Sobel, Dava. Longitude. Print.