Wednesday, December 25, 2013
How to use your hand and the sun to tell the time
As you know, the sun crosses the imaginary North-South line (Meridian) every day when it reaches its highest point (Zenith) above the horizon. Therefore when the sun is at its highest point in the sky it is North or South of you, depending upon your position on the earth's surface, and the sun's position relative to the earth's equator.
For all practical purposes there are twenty-four hours between each sun crossing of your North-South line, or Meridian. During the twenty-four hours the earth will have revolved apparently 360 degrees; therefore it will move 15 degrees for each hour, or one degree in four minutes.
This is very convenient to know, because if you know the North or South accurately, you can easily measure off the number of degrees the sun is from the North-South line, and this will give you the number of hours and minutes before, or after noon. These measurements must be made along the curved path of the sun, and not on a horizontal or flat plane.Source: This article was adapted from The Ten Bushcraft Books, by Richard Harry Graves. Originally a military jungle-craft manual, it was published circa-1944 by Graves (1898-1971), an Irish-born Australian poet and novelist who founded and led the Australian Jungle Survival and Rescue Detachment during World War II. Attached to the Far East American Air Force, he trained US forces in jungle craft. His 60-man unit conducted over 300 rescues, all of which were completed successfully and without losses. After the war he ran a bushcraft school for over twenty years.
The above illustration shows how to measure degrees with the arm fully extended. These measurements will vary slightly, like your personal dimensions, and should be checked by each individual with a compass for accuracy.
- Hand at full arm's length, fingers widely spread—22 degrees
- Thumb turned in—15 degrees
- Closed fist—8 degrees
- From second knuckle to edge of fist—3 degrees
- Between two centre knuckles—2 degrees
By this means, if you have a compass, time can be easily read from the sun's position. This should be possible to within four or five minutes. Decide from your compass your true North-South line and remember to make allowance for the magnetic variation from True North. Measure the number of degrees the sun is from this imaginary line, and multiply the number of degrees by four to obtain the number of minutes.
For example, in the above illustration, the sun is 34 degrees from the North-South line. It is morning, because the sun is on the eastern side of the North-South line, 34 x 4 = 136 minutes before noon; therefore it is sixteen minutes to ten in the morning local sun time.
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