Latitude and Longitude

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Latitude and Longitude
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Latitude

• Latitude lines are imaginary horizontal lines on
  a world or large area map. Latitude lines
  separate the world into Northern and Southern
  hemispheres and range between 0 degrees at the
  Equator and 90 degrees at the North and South
  Poles.

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Longitude

• Longitude lines are imaginary vertical lines on a
  world or large area map. Longitude lines separate
  the world into the Eastern and Western
  hemispheres and range between 0 degrees at the
  Greenwich Meridian (also known as the Prime
  Meridian) and 180 degrees east and west of
  Greenwich at the International Date Line.

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• Each degree of latitude and longitude is
  subdivided into 60 equal parts called minutes and
  each minute is divided into 60 equal parts called
  seconds. On the surface of earth, one degree of
  either latitude or longitude is about 110 km (69
  miles) although it is slightly more at the poles
  as the earth is not a perfect sphere.

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Latitude and Longitude

• The earth is divided into lots of imaginary lines
  called latitude and longitude.

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Lines

• Longitude lines run north and south.
• Latitude lines run east and west.
• The lines measure distances in degrees.

Latitude
Longitude
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Where is 0 degree?

• The equator is 0 degree latitude.
• It is an imaginary belt that runs halfway point
  between the North Pole and the South Pole.

Equator
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Where is 0 degree?

• The prime meridian is 0 degrees longitude. This
  imaginary line runs through the United Kingdom,
  France, Spain, western Africa, and Antarctica.

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Latitude Longitude
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Hemispheres

• By using the equator and prime meridian, we can
  divide the world into four hemispheres, north,
  south, east, and west.

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History

• Whilst early sailors could easily calculate
  latitude, the calculation of longitude was
  inaccurate on long voyages out of sight of land,
  and these voyages sometimes ended with shipwrecks
  resulting not only in loss of life, but also loss
  of extremely valuable cargoes being shipped from
  Europe to the Americas.

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• Galileo had suggested a method of calculating
  longitude based on observing the relative
  positions of Jupiter's natural satellites, which
  have distinct known orbits. However, unless you
  had a professional astronomer at sea with you, it
  was almost impossible to calculate your longitude
  and even if you did, the natural motion of a ship
  on the ocean made it difficult.

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• The other problem was the location of the Prime
  Meridian. Portuguese map-maker Pedro Reinel first
  drew one on a map in 1506, fixing it at the
  Madeira Islands. As the secret of navigating the
  South Atlantic spread, many powers used the
  Portuguese starting point, while others started
  to use their own territories - Spain set theirs
  in the Canary Islands and the English used
  Greenwich for 0o longitude.

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• It became clear that the only way longitude could
  be calculated with any precision was to use
  accurate clocks. For every 15 that one travels
  eastward, the local time moves one hour ahead and
  every 15 westward, one hour back from that at
  the Prime Meridian. So, if you had two clocks on
  board one telling the time at the Prime
  Meridian and the other adjusted for local time at
  noon each day, then you can calculate how far
  east or west of 0 you are.

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• The problem was that early clocks were not nearly
  accurate enough on land, but at sea the motion of
  ships knocked the clock out by several minutes a
  day resulting in ships hitting rocks they thought
  they were miles away from.

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• One example of this and the one that proved a
  turning point in the longitude problem was the
  wrecking of the British Fleet led by Sir
  Cloudesley Shovell on 22 October 1707. Shovell
  was a British hero with a celebrated naval
  career, including an important role in the
  capture of Gibraltar in 1704. He was returning
  from the Mediterranean on HMS Association,
  commanded by Captain Edmund Loades when she
  struck Outer Gilstone Rock off the Isles of
  Scilly, and was wrecked with the loss of her
  entire crew of about 800 men, a huge cargo of
  silver bullion and three other ships (including
  HMS Eagle and HMS Romney). As a result of an
  error in longitude calculation, the ships were
  not where they were reckoned to be.

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• Largely as a result of this disaster, the Board
  of the Admiralty instituted a competition for a
  more precise method to determine longitude. This
  led to the British Longitude Act in 1714, which
  created the Longitude Prize of 20,000 for anyone
  who could devise a practical method of
  determining longitude at sea to within half a
  degree (2 minutes of time) of accuracy on a trip
  to the West Indies.

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The Longitude Prize

• A body known as the Board of Longitude was set up
  to administer and judge the prize.

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• John Harrison was a joiner by trade who had made
  several cutting edge clocks - with wooden
  mechanisms, some needing no lubrication, and he
  invented a pendulum rod for his long case clocks
  which meant they had an accuracy of one second in
  a month.

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•  Harrisons first attempt at the Longitude Prize,
  H1, was constructed between 1730 and 1735. It
  contained a number of springs to counterbalance
  the workings making it independent of the
  direction of gravity which was crucial at sea. To
  test the clock, Harrison travelled to Lisbon in
  1736 and found that the clock lost 4 minutes
  during the initial part of the voyage but kept
  good time for the return leg. In fact Harrison
  placed the ship some 50 miles west of the
  position determined by the ship's official
  navigator. Visual land observations revealed that
  Harrison was correct, and resulted in the
  prevention of the ship being wrecked off the
  coast of Cornwall. On this basis, he applied for
  more financial assistance from the Board of
  Longitude to make an improved version, H2.

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• H2 was large and heavier than H1 but was a
  similar design. Harrison worked on it from 1737
  1740 but realised its design was wrong because
  the bar balances did not always counter the
  motion of the ship. He worked on his next design,
  H3, from 1740 1759. The clock worked fine when
  the ship ran with the wind but tacking as it
  sailed against the wind caused it to run slow.

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•  His next attempt, H4, was a totally new and more
  compact affair 13cm in diameter and weighing
  1.45kg, and based on a temperature compensated
  balance wheel which is found in virtually every
  non-electronic watch today. It was this model
  that was presented to the Board of Longitude, and
  the West Indies trial required by the Longitude
  Act. By this time Harrison was too frail to
  undertake sea trials himself and so his son
  William set sail for the West Indies on the ship
  Deptford on 18 November 1761.

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• The watch kept the time for Greenwich during the
  voyage whilst the local time of the ship was
  determined using standard solar observations.
  When they arrived in Jamaica on 19th January 1762
  the watch was only 5.1 seconds slow and the
  calculation of the ships position was only 2
  miles in error which was better then the half a
  degree required to win the prize.

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• Getting the prize money from the board was a
  different matter, however. Seemingly they didnt
  want the award going to a working class
  carpenter, but rather a gentleman. A second sea
  trial was arranged and again William set sail on
  the Tartar on 28th March 1764 heading for
  Madeira. On this trip the error was only 39.2
  seconds over a voyage which lasted 47 days 3
  times the accuracy needed to qualify for the
  Longitude Prize.

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• The Board of Longitude were not satisfied that
  the watch wasnt a fluke and refused to hand over
  any money until copies could be made and tested.
  They agreed to pay him half of the money upon
  disclosure of the workings of the clock to the
  Astronomer Royal and give him the rest when
  copies were made which had the same accuracy.

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• Initially Harrison refused to accept this
  arrangement but it became clear that unless he
  backed down he would never win the Prize. So, in
  August 1765 a panel of experts examined the watch
  at Harrisons house in London and signed a
  certificate confirming that they had seen the
  full workings of the watch. The Board then asked
  Harrison to recommend someone to copy H4. He
  suggested leading watchmaker Larcum Kendall, and
  was given the first half of the Prize.

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• Things became more difficult for John Harrison as
  he chased the second half of the Prize. He was
  required to produce 2 more copies of H4 and have
  them tested. Harrison was now in his seventies
  and he worked with his son on a new timepiece,
  H5, while Kendall worked on the copy of H4 called
  K1.K1 was finished in 1769 and Harrison
  confirmed it was an exceptional copy. He asked
  the Board of Longitude to accept K1 and H5 as the
  copies of H4 for the test but this was refused,
  with the Board stipulating that both copies must
  be made by the Harrison's. 

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• This made John angry and on 31st January 1772,
  aged 79, he appealed to King George III via a
  letter to his private astronomer at Richmond, Dr
  Stephen Demainbray. Harrison was summoned to meet
  the King after which the King is reported to have
  said these people have been cruelly wronged and
  by God I will see them righted.

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• The King himself put H5 on trial in 1772 and it
  performed superbly. However, the Board of
  Longitude refused to accept the results of this
  trial and so the Harrisons petitioned
  Parliament. As a result, they were finally
  awarded 8750 by an Act of Parliament in June
  1773. John Harrison died in London on 24 March
  1776, his 83rd birthday 3 years after being
  finally recognised as having solved the Longitude
  problem.

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• An interesting aside is that K1 was used by
  Captain Cook on his second voyage of discovery
  which took in the Tropics and the Antarctic.
  Throughout the whole 3 year journey the daily
  rate of K1 never exceeded 8 seconds
  (corresponding to 2 nautical miles at the
  equator).

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• It should be noted that Harrison's H-4 marine
  chronometer did not keep precise time. That would
  have been well beyond the technology of the time.
  What Harrison's chronometer did achieve was that
  would run fast or slow at a more or less even
  rate averaged out over time once it had been set
  at Greenwich. Thus the time at Greenwich (or
  Greenwich Mean Time) could be ascertained to
  considerable accuracy by correcting the
  chronometer by the known error since it was last
  set.

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• Harrisons design for marine chronometers was so
  good that even though other craftsmen found other
  ways to manufacture them, his template remained
  in use until microchips heralded the use of
  electronic chronometers

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• The Royal Observatory is the home of Greenwich
  Mean Time as it has been the source of the
  official Prime Meridian of the world, Longitude
  0 0' 0'' since 1884. Every place on the Earth is
  measured in terms of its distance east or west
  from this line. 

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• Prior to 1884, different countries used their own
  Meridian lines but as marine exploration became
  increasingly common there was a call for
  standardisation of the meridian and therefore
  world time. In 1884, 41 delegates from 25 nations
  met in Washington D.C. at the request of
  President Chester Arthur at the International
  Meridian Conference. By the end of the
  conference, Greenwich had won the prize of
  Longitude 0º by a vote of 22 to 1 against (San
  Domingo), with 2 abstentions (France and Brazil).

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• There were two main reasons for choosing
  Greenwich. Firstly, the USA had already chosen
  Greenwich as the basis for its own national time
  zone system and secondly, 72 of the world's
  commerce depended on sea-charts which used it as
  the Prime Meridian. Therefore the Prime Meridian
  at Greenwich became the centre of world time,
  Greenwich Mean Time (GMT).

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World time

• At the conference, the proposal of the Canadian
  Sir Sanford Fleming to split the world into 24
  time zones, each 15 degrees of longitude in width
  was accepted too. Time in these zones used to be
  measured relative to GMT, with midday defined as
  the time at which the sun crosses the Prime
  Meridian.

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World time
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• Time zones westward of Greenwich advance by an
  hour each time and those eastward go back by an
  hour each time. There is no international law
  governing the location of the boundaries of time
  zones or time internationally and so national
  boundaries and political matters influence the
  shape of the time zone boundaries. For example,
  China uses a single time zone (eight hours ahead
  of Coordinated Universal Time) instead of five
  different time zones.

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GPS

• With the advent of the GPS satellite system in
  the 1980s, accurate navigation could be done by
  anyone with a hand held device which could access
  satellites orbiting the Earth. The system can
  calculate position by receiving and comparing
  time signals from any three GPS satellites based
  on an internal map of the world in the form of
  a computer program. Because the earth has a
  complicated shape based on a sphere, the only way
  to develop the map was to produce a best fit
  based on an earth geodetic model WGS-84. This
  doesnt fit the Earths surface exactly
  everywhere but juggles the map shape to find the
  position where it fits best at the most places it
  can.

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• Unfortunately because of this, the WGS84 meridian
  used by Keyhole, Google Earth and all GPS
  applications such as SatNav systems in cars and
  cruise missiles is 102.5m to the east of the
  official Prime Meridian as shown here.

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Latitude and Longitude.

• Longitude lines
• run up and down the map
• measured in degrees
• east and west
• of the Greenwich Meridian
• they converge at the Poles
• they are all the same length

• Latitude lines
• run across the map
• measured in degrees
• north and south
• of the Equator
• they are parallel
• decrease in length towards the Poles

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Interactive Site

• http//www.lakelandsd.com/tutorial/lesson1.html

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Important Lines of Latitude and Longitude
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West
0º
East
180º
North
66½º
Arctic Circle
Tropic of Cancer
23½º
Equator
0º
23½º
Tropic of Capricorn
International Date Line
Greenwich Meridian
Antarctic Circle
66½º
South
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Latitude and Longitude Resources

• A Printable Latitude Longitude Map of the World
• Latitude and Longitude Quiz
• http//olc.spsd.sk.ca/DE/k9mod/Mapskill/mod3fl5.sw
  f Try this interactive
• http//www.kidsgeo.com/geography-games/latitude-lo
  ngitude-map-game.php Try this game