06 October 2008

Crossing The Prime Meridian!

Today at 6am we sailed over 0° longitude and now we are back in the western hemisphere. We crossed the 180° line back in Fiji, so I guess Fiji is directly under us now.

For a reading lesson check out the book 'Longitude' and you will find out why the 0° longitude line passes right through Greenwich, England. Hence the term "Greenwich Mean Time". Or read my history lesson kids...

Old day sailors using sextants or quadrants were able to fix their latitudes quite easily. But they could not figure out what their longitude was. Most ships would see on a chart what the latitude of where there next port was. Then they would just sail down that line until they ran across it guessing their distances by dead reckoning.

When Columbus sailed on his many trips to the Caribbean and back, this is how he navigated, by running down lines of latitude. Many ships were lost this way and the Queen of England put out a reward for the first person that could come up with a solution. Many of the Queens 'experts' thought that by doing all kinds of crazy math formulas, using a sextant/quadrant to shoot star positions, that they could find longitude. But it was entirely too confusing and unreliable.

An unknown English clock maker (before wrist watches) John Harrison thought that if one could tell the exact time at sea and compare a star fix in their present position to what the position would be in Greenwich England at a set time using an almanac, then one could determine longitude. This was before anyone had figured out how to make a pocket watch and most all clocks were pendulum clocks, meaning that there was no way a clock would work on a rolling boat.

It took John Harrison several years, but he made a portable clock the size of a large box. All the internal parts were made out of hardwoods as this clock would have to endure hot humid conditions to freezing cold without having any of the clocks parts expanding of contracting. His clock had to keep accurate time for sometimes over a year on a pitching boat in any weather conditions.

Once he made his first clock and showed it to the Royal Observation Society, they thought he was a bit of a nut. They had the smartest guys in England already working on huge books of calculations for every star in the sky, but still could not plot longitude. Instead of rewarding him and using his clock technology, then made him go to sea with his clock to the Caribbean to prove its usefulness. After a year later he returned back to England with his trusty clock still keeping time. And his ship's captain was able to determine longitude during this trip using Harrison's clock. It took the Royal Society some time, but they finally gave him credit and the reward.

The Royal Observatory is at Greenwich England, and this is why 0° is where it is.

I am writing this all from memory. So hopefully I got it right. But anyway grab, the book 'Longitude' as it is a great read and I have read it 3 times. I am sure they would have loved to have electronic charts and GPS. But back then having a clock at sea was pretty high tech.

I have never been to England, but from what I have read if you go the Maritime Museum in Greenwich England all the clocks John Harrison made are on display and they still work! One of them was taken by Captain James Cook on his explorations around the world.

If you really want to read more on longitude and early exploration check out the book '1421 - The Year China Discovered America' about the early Chinese explorers and how they figured it out and pretty much mapped out the world in 1421 with great accuracy. That is another great book that I have read twice now. Not many Western history buffs are fans of this book, but it is pretty hard to argue with the facts presented.

There's your history lesson for the day!!

Notes From Ron:

  • The BBC did a TV drama adaptation of the book "Longitude" which you can rent. It is long, over 4 hours. They wove together the story of Rupert Gould with John Harrison. Gould is the man who after WWII "re-discovered" Harrison and got the original Harrison clocks working again.
  • PBS's Nova program has an excellent website to go with their TV show "Lost At Sea - The Search for Longitude", which you can also rent. It also tells the story of Harrison without all of the drama that the BBC put in to their show.
  • Columbus discovered America in October 1492, which is 71 years after the Chinese found it according to the "1421" book.
  • As Tom mentioned, the way sailors use to cross the oceans was to sail north or south until they reached the latitude they desired. Then they would head due east or west. Hence the old saying for British sailors going to the Caribbean "Head south 'till the butter melts, then turn right." This method also worked meshed perfectly with the trade winds, which constantly blow from the NE or SE around the planet.
  • Actually, Harrison was never given his full credit and reward for solving the problem. The Royal Observation Society just couldn't admit that a common self taught clockmaker had solved what they couldn't with all their university degrees and equipment. King George III of England had to intervene and demand that that Harrison be given the award. They only gave him part of it.
  • The term Greenwich Mean Time (GMT) is not used anymore. Now the world uses UTC (Universal Time Coordinate). You might have also heard this time referred to as Zulu Time in aviation.
  • I went to the Royal Observatory in Greenwich, England last year when I was doing some some work in London. On the grounds of the observatory is a long brass line between the bricks indicating the Prime Meridian. Here is a photo of it. Greenwich a great little place and I highly recommend that you stop there if you are in London. You can take a ferry from central London. Unfortunately for me, I arrived the day after the Cutty Sark caught fire, and the Gypsy Moth IV was gone on tour.
  • The way Harrison solved the Longitude Problem is very simple. Ships carry with them one of his clocks that shows what time it is in Greenwich, England. When it is exactly noon on board the ship (when the sun is at its highest point in the sky), they note the time on this clock. The difference between local noon and Greenwich time is their longitude. For example, if their local noon is exactly 1 hour after Greenwich noon, then they are 15 degrees west of the prime meridian. 15 is 360 divided by 24. There are 360 degrees on the compass, and 24 hours in a day. The sun crosses 15 degrees of longitude every hour.
  • With the help of an almanac, you can also used fixed stars, the moon, and other celestial objects to get a "fix". That way you can get your longitude at night, or when the sun is at another position in the sky.
  • The dead reckoning method used to guess longitude before Harrison's solution was to measure speed in order to compute the distance traveled every day. Once the ship turned right or left at the longitude they desired, they could only guess at the distance traveled and subtract that from the distance expected. That way they would know when they were approaching land, or at least their best guess.
  • In order to measure speed, they would use a chip log. A chip log is a barrel with a rope ties to it. The rope had knots in it every 47 feet, 3 inches. They would toss the barrel overboard and using an hourglass, count how many knots would play out in 30 seconds. Hence the term "knots" to indicate speed.
  • At the time that the Prime Meridian was designated as running through Greenwich England, the British Empire was the world's foremost superpower. Greenwich just happened to be the place where the Royal Navy got their almanacs from since that is where a long time before a king had built an observatory. It was close enough to London to easily get to, yet far enough away to get away from the lights. Plus Royal Navy ships could stop on their way to sea down the Thames. The French, being the other world superpower in competition with the British, were mighty upset about this and demanded that the PM go through Paris, a few degrees to the east. In fact, many countries created their own PM's for their own charts. It wasn't until 1884 that the everyone agreed to use Greenwich as the PM.
  • Earlier this year Muslim scholars demanded that the world change to Mecca Time and run the PM through the Grand Mosque in Mecca. They felt that since Mecca is the center of the world, it only makes sense that the PM go through it.
  • Here is the really cool part. The choice of Greenwich for the PM worked out perfectly because of the International Date Line (IDL), runs right down the middle of the Pacific Ocean. The IDL has to be at 180 degrees, the other side of the planet, from the PM. The 180th longitude runs between Alaska and Russia, and pretty much misses all land masses on the planet. It does cross a few small islands. But on the whole, there is simply not a better place on the planet to put an IDL. If the IDL had been decided first, which could have only been possible after exploring and charting the whole planet, then Greenwich would have been the location of the PM, 180 degrees away from the IDL. How is that for fortunate luck? If France, Rome, Berlin, or Mecca had won the argument for "owning" the world's official PM, then Alaska would have to be in tomorrow.
  • As you can tell, I love this stuff. :-)

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