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Use a wristwatch and the sun as a compass

Science Projects - Earth Science and Astronomy

Suitable For

Grade 7

Difficulty

1

Time Required

 <1 Hour

Supervision

Advised

What’s it about?

A very old method of finding north without a compass is by using your wristwatch, the sun and a thin stick. Even though this method to find your direction is not very accurate, Boy Scouts swear by it! Astronomers, explorers and other professionals however, do not deem this method as very reliable, and would need to use more precise equipment for more accurate readings. Find out for yourself how accurate this method of finding true north is in the following science experiment:

Topics covered

Magnetic North, True North

What will I need?

  • WRISTWATCH
  • TOOTHPICK
  • COMPASS

Procedure (Method)

A very old method of finding north without a compass is by using your wristwatch, the sun and a thin stick. Even though this method to find your direction is not very accurate, Boy Scouts swear by it! Astronomers, explorers and other professionals however, do not deem this method as very reliable, and would need to use more precise equipment for more accurate readings. Find out for yourself how accurate this method of finding true north is in the following science experiment:

Science project diagram
  1. Sometime during the day, hold your arm with your wristwatch out horizontally with the face of your watch facing directly up. A digital watch will not work!
  2. Hold up any thin stick, such as a toothpick, vertical to the face of the watch, in the centre.
  3. Now, turn your body and the watch horizontally until the shadow of the stick is directly along the hour hand of the watch.
  4. True north will be more-or-less in the middle between the shadow of the toothpick, and the 12 hour mark!
  5. Do this several times a day and compare your results with a magnetic compass, to see how close it is to true north.

How does it work?

This science experiment works because as the sun moves across the sky from east to west, its shadow gradually changes during the day, and thus its shadow can be used to find the north / south line at any time of day during which the sun is present. This method can be used even when it is pretty foggy. Although you may not be able to see the sun, it may still cast a faint shadow. For most accurate results, set your watch to ‘true’ local time, in other words without adjustments for daylight savings time.

When checking your results with a magnetic compass, it will deviate slightly because compasses point to magnetic North, which is more than 1600km away from the true north pole. Magnetic north is always moving slightly, and we call this margin of error declination. Declination is an angle that measures the difference between true north and magnetic north. The angle varies depending on where you are on the planet.

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