The Sundial “Clock/Compass”



In response to an article I posted on being able to find the North-South direction line using your watch as a sundial-like tool, a reader pointed out that this “survival skill” only worked with an analog watch because of its clock face and hour hand; he deemed a digital watch to be completely useless. I was disappointed by his response—and grateful!

Disappointed because perhaps I had failed to convey the “why” for the basis of this skill, and grateful because he had touched on the very fundamental aspect of any learned skill—knowing the reason you are trying to accomplish a certain task . “Why” being more important than“what” or “how”—and beyond just the physical aspects of being able to accomplish your goal.

Why do we need the watch for this exercise? We need to know what time it is! It doesn’t matter if we hear it on a radio, use our cell phone, or get it from a super slick digital watch. The time of day is critical because the sun’s position along its arc across the sky is relative to the 24-hour segmented day. At its highest point along the arch, it’s noon, 12 p.m. Several degrees along that arc, either before or after its zenith, and it’s either earlier or later than 12 p.m. and hence, a little bit more easterly or westerly of “high noon” when its position above the horizon is due south. Using that relative position along the arc and knowing the time, we can fairly closely determine south and mark the North-South line on the ground.

The key is knowing what time it is without needing a particular device to give us that info. Once we know the time we can create a clock face—either on the ground, a piece of paper, or even roughly imagining that clock on the palm of our hand, our fingers becoming the hour hands. Here’s how that works:

Determining North-South Line if Time is Known

  1. Determine the time
  2. Create a bare clock face (essentially a circle without any hands)
  3. Position a marker stick along the edge of the circle until its shadow falls through the center of the circle/clock face
  4. The shadow marks your hour hand for the current time
  5. Using that hour as a starting point, mark out all the other hours along the face of your “clock”
  6. Determine 12 on the clock face and find the center of the arc on the rim of the clock exactly half way between “noon” and the hour marked by the shadow
  7. A line drawn from that half way point, through the center of the clock is your North-South Line, south being towards the sun.

This has an accuracy of about 15-20 minutes depending on how refined your steps were, but it will give you a good indication where the key points of the compass are.

This is all pretty basic, taught as a fundamental skill in most all outdoor, self-reliant instruction. Taking it from the other end, working from a known North-South line, you can learn what time of day it is with the same amount of relative accuracy. Simply work the process backwards:

Determining Time if Direction is Known

  1. You know the North-South line is half way between noon and the hour of the day
  2. Create your clock face as before, but this time add your North-South line out from edge to the clock’s center
  3. Use a stick to lay a shadow across the clock face, again having it fall from the clock rim through the center; this marks the unknown “hour”
  4. Divide the clock face into 12 hour increments using your unknown hour hand as your starting point
  5. Count back the marks from the shadow hour hand to the North-South line; (let’s say it was 2.5 units)
  6. Now continue counting another 2.5 units beyond the North-South line and mark that as 12
  7. Remember that the North-South line is half way between noon and the hour, and you’ve just determined all those positions, you can now simply count forward from noon to the unknown hour and determine the time it represents. In our scenario, there are five hour marks between the shadow and our noon, so the approximate time is 5 p.m.

It’s always important to know the principles behind the skills you are learning, particularly in an environment that is ever-changing and may not have all the resources you are most familiar with for completing a learned task. Be safe. Be smart. And have fun!



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2 Responses to “The Sundial “Clock/Compass””

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    Doesn’t matter how old I get, I always find it amazing to think you can tell time from the sun. This is one of the first things I teach my intro to survival skills classes. Because if you can’t get your bearings without a compass…well….

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      Tom Watson

      In all my presentations on self-reliance/survival I stress knowing the “why” behind what you are doing, what you are trying to accomplish. Thinking on your feet, and not relying solely on technology goes a long way in taking care of one’s self in the outdoors. We’re not all trying to evade the enemy behind their lines as so many survival training Rambo’s like to pretend, it’s getting through an emergency situation as a regular outdoor recreationist that truly challenges most of us…