Good approximation to solar declination by a watch face

Good approximation to solar declination by a watch face

by tonytran2015 (Melbourne, Australia).

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(Blog No.53).

#solar declination, #watch face, #multi-dial watch face, #Solar navigation, #find North, #time, #survival.

The value of solar declination is needed for accurate determination of North direction and time using a divider or a watch (references [1], [2]). Good approximation to solar declination is required by the methods to produce accurate results in cold temperate zone and arctic zone. The required value of solar declination can be simply obtained using only a watch face or even the drawing of a watch face on the ground.

1. Method

solar-declination-by-a-watch-face

Figure: Determining solar declination using a watch face. (The lines SOLAR DECLINATION Its rough estimate is required for Fine Alignment of the watch are to be ignored.)

Draw the dial of an upside-down watch face as a small sub-dial of a watch face (on its 3 o’clock side) as in the figure. The radius of the sub-dial should be close to the length of 4 minutes markings on the rim of the main dial.

The four numbers 6, 9, 12, 3 on the rim of the upside-down sub-dial correspond to 21/6, 23/9, 21/12, 21/3 respectively. They are the dates on the calendar. Your current date gives a point on the rim of this sub-dial.

Project the point of your current date horizontally onto the rim of the main dial. The angle from the direction of 3 o’clock to that of a main long hand pointing to the projected point is equal to the angle of solar declination.

The angles from the Northern and Southern Celestial poles to the Sun are just the angles from the 12 o’clock and 6 o’clock directions respectively to that of the above main long hand.

2. Applications to survival situations

Most multi-dial watches and chronograph watches already have sub-dials made with the sub-dial radius being close to 4 minute length on the rim of the main dial. This method can be conveniently applied to any such watches having their sub-dials on either the 3 o’clock or 9 o’clock side.

When having no actual watch face, you can draw a watch dial and a sub-dial on the ground to determine solar declination.

Accurate value of solar declination improves the accuracy of the determination of North direction using a divider or a watch (references [1], [2]) when the Sun has low altitude in the cold temperate and arctic zones.

References:

[1]. tonytran2015, Finding directions and time using the Sun and a divider., Additional survival tricks, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/05/06/finding-directions-and-time-using-the-sun-and-a-dividing-compass/, posted on May 6, 2015.

[2]. tonytran2015,  Finding accurate directions using a watch,  Additional survival tricks, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/05/19/finding-accurate-directions-using-a-watch/, posted on May 19, 2015.

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