6 Oct 2012

Celestial Navigation

by Joan Marie Galat

Imagine you’re a sailor more than 300 years ago. A storm takes you out of sight of land and you don’t know your location. You worry you could run out of fresh water and food or pirates might attack. Clouds hide the Sun and make it difficult to tell your direction. You have a compass but maps in the 1700s are not very accurate. With night coming, all you can do is hope your ship doesn’t hit any rocks.

Now suppose your only compass falls into the sea! Good thing you know a bit about celestial navigationIf the Moon should rise before the Sun sets, you will be able to tell your direction. The rising Moon is illuminated on its west side because the Sun sets in the west. But if you look after midnight, the eastern side is lit.

If the sky clears you’ll be able to find Polaris, the North Star. You can use your sextant to measure the angle of a star or other celestial body. This tells you your latitude—how far north or south you are from the equator. Celestial navigation can save your life. But you still need to know your longitude—your direction east and west.

A carpenter named John Harrison spent many years trying to solve the problem of determining longitude at sea. He realized that if you knew the time at a specific location on land, as well as your exact time at sea, you could figure out your longitude. Unfortunately, time pieces were not very accurate at this time. Clocks with pendulums could not keep accurate time on a boat.

Harrison devoted his life to solving the problem but it took the King of England to make sure he got the recognition he deserved. Thanks to Harrison’s work, everyone on Earth recognizes the same time zones. 

You can read his story in my newest title, The Discovery of Longitude. This historical picture book for ages five and up
is published by Pelican
Publishing Company. Visit www.joangalat.com for details.

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