Introduction: Finding North With a Watch More Accurately

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by tonytran2015 (Melbourne, Australia)

This method uses a common 12-hour watch with analogue face for finding directions. Unlike the traditional method of using the hour hand of a flat lying watch, my method uses a watch tilted from the vertical and gives better accuracy for both North and South hemispheres including tropical zones. When applied to the arctic and antarctic regions, the watch is tilted by more than 67 degrees and lies almost flat on the ground; it becomes the traditional method using flat lying watch.

This method uses the position of the Sun, time and known latitude angle to determine directions and Sun declination (therefore estimation of current month of the year).

Step 1:

Method for Northern latitudes.

The word “bisector” here is used to mean the bisector of the angle between the midnight/midday marking and the hour hand.

1/- Hold the watch so that its AXIS rises above the horizontal plane by an angle equal to the latitude of the region. That is its face points to somewhere in the sky and its back is angled downwards into the ground.

2N/- Determine the half-plane limited by the axis of the watch and containing the bisector. This half plane revolves clockwise about the axis of the watch once every 24 hour and goes through the mid-day marking at noon.

Step 2:

The red line is the bisector. The line CB is drawn on a card representing the half-plane to enable accurate alignment to the Sun.

Step 3:

3N/- Determine on the semi-plane a half-line CB from the center C of the watch dial, forming with the watch axis an angle equal to the angle between the direction to the Sun and the Celestial axis. The half-line CB starts from the center of the dial and is nearly in the direction of the bisector. It rises above the dial toward the glass and points through the glass of the watch during summer time and dives below the dial into the movement compartment of the watch and points through the movement of the watch during winter time. This half-line always points to the Sun if this watch displays the local time and the face of the watch and its axis point to the North Star.

Step 4:

Figure: Summary of the finding North by a watch.

4N/- Hold the watch in such composure and rotate your whole body around your vertical axis by your feet until the Sun lies in the above half-plane, which is denoted by the magenta flag in the following photo. Instead of trying to have the half-plane containing the Sun, observer can try to point the half-line CB towards the Sun. This gives better accuracy.

Step 5:

Figure: Summary of the finding North by a watch. Red hand is the bisector of 0 hr direction and the hour hand; green hand is its reflection across the (6-12) axis. Axis C-BN for Northern hemisphere is parallel to red hand at equinox days and is (raised above)/(dipped below) the watch dial by 23 degrees at local summer/winter solstice. Green drawing marks are for Southern hemisphere and are the mirror reflection of red drawing marks.


5N/- At that position, the watch face and its AXIS are POINTING to the North Star. Tilt the watch further, until it lies horizontally. In this horizontal position, the mid-day marking is pointing South and the 6 o’clock marking is pointing North.

There is a part 2 for Southern latitudes [1] and a caution note on using old methods [2].

I also have a method of finding North direction and approximate time with bare hands [3], which is more difficult but is applicable in difficult situations and you may be interested in.

References.

[1]. tonytran2015 (Melbourne, Australia), Finding North with a watch more accurately p2, Instructables, https://www.instructables.com/id/Finding-North-with..., posted on May 25, 2015
[2]. tonytran2015 (Melbourne, Australia), Caution in finding North by bi-sector line, Instructables, https://www.instructables.com/id/Caution-in-finding..., posted on Jun 11, 2015

[3]. tonytran2015 (Melbourne, Australia), Finding North direction and time from the Sun using bare hands, Instructables, https://www.instructables.com/id/Find-North-direct..., posted on May 29, 2015