Longitude 3 - Answers

© National Maritime Museum, Greenwich, London

Solving the problem- clocks and stars


1. Clocks and pocket watches were made before 1714. Why would they not have been suitable for telling the time at sea?

Sailing ships were wet, very hot or very cold and always moving.Salt water corrodes metals and temperature changes make the mechanism unreliable due to thermal expansion of parts.

2. Astronomical observations can be used to measure time, for example the timing of the orbits of the moons of Jupiter. Why would making those observations be difficult at sea?

Isaac Newton himself said that it was simply too difficult to use a telescope on board a ship. You can try this with a pair of binoculars. Without any support, try to find a planet and focus on it. Now imagine that you are on a moving ship. How difficult would it be?

3. In the eighteenth century, naval navigators were highly skilled in maths and astronomy. They were also all men! In the modern services are science skills still needed and are women likely to be equal to men in these skills?

Modern navigators use complex scientific equipment and need to be good at maths and science. Most astronauts come from the military services and have very high level science skills.



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© National Maritime Museum, Greenwich, London

© National Maritime Museum, Greenwich, London
Finding longitude was not all about clocks. Captain Cook made successful use of astronomical tables and accurate observations. He also used Harrison's watches on later voyages.

Credit: NASA
Today's explorers are also scientists. This is another captain, Samantha Cristoforetti, a Captain in the Italian Air Force, running experiments on board the International Space Station in April 2015.