These days that question is easy to answer. If in doubt, pull out your smart phone and check your coordinates. But it's not so long ago that people died for not knowing where they were. Many ships got lost at sea, crashed into rocks or ran aground because sailors couldn't figure out their longitude.

The book Longitude by Dava Sobel tells the fascinating story of that tricky coordinate, why a prize was put on its head and how the puzzle was finally solved by means of a clock. This "true-life thriller" is one of our favourite popular science books ever!

If you've already read the book, or need to pass the time until it turns up under the tree on Christmas day, then read about the maths of navigation on Plus:

• Time and motion tells you why getting from A to B is harder than you think.
• Conic section hide and seek explores how ancient maths can find people who are lost or hiding.
• Finding your way home without knowing where you are explains how insects navigate.
• On thin ice is a package we produced for use in the classroom, based on the maths of navigation.

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