How to use the Sun and shadows for navigation.
The earth’s relationship to the sun can help you to determine direction (celestial navigation). The sun always rises in the east and sets in the west, but not exactly due east or due west. There is some seasonal variation in the exact direction that the sun sets – the sun rises due east only two times per year ((the equinoxes).
Shadows will move in the opposite direction of the sun (shadows move from west to east). At high noon, shadows will point towards the north (in the Northern Hemisphere) or south (in the Southern Hemisphere). There are various methods you can use to determine the time or direction using the sun and shadows.
Shadow-Tip or Shadow Stick methods
In the shadow-tip method, find a straight stick 1 meter (3 feet) long, and a level spot free of brush on which the stick will cast a clear, even shadow. This method is simple and fairly accurate (the further you are from the equator, the more accurate this method is). The Shadow Stick method consists of four steps:
- Place the stick or branch into the ground at a level spot where it will cast a distinctive shadow. Mark the shadow’s tip with a stone, twig, or other means. This first shadow mark will be our “west” marker.
- Wait 10 to 15 minutes until the shadow tip moves a few centimeters. Mark the shadow tip’s new position in the same way as the first. This mark will be our east marker.
- Draw a straight line through the two marks to obtain an approximate east-west line.
- To determine north, stand with the first mark (west) to your left and the second mark to your right—you are now facing north. This fact is true everywhere on earth.
Alternate Shadow-Tip method
An alternate Shadow-Tip method is more accurate than the traditional method but requires more time. The two points you determine will provide east/west direction as long as the two points are exactly the same distance from the center stick.
- Set up your shadow stick and mark the first shadow in the morning.
- Use a piece of string and a second stick to draw a clean arc through this mark and around the stick.
- At midday, the shadow will shrink and disappear. In the afternoon, it will lengthen again and at the point where it touches the arc, make a second mark.
- Draw a line through the two marks to get an accurate east-west line.
The Watch Method
You can also determine direction using a common or analog watch—one that has an hour and minute hand. The direction will be accurate if you are using true local time, without any changes for daylight savings time. As with the Shadow-Stick method, the further you are from the equator, the more accurate this method will be. If you only have a digital watch, you can draw a clock face on a piece of paper, marking the correct time on it, and use it to determine your direction.
In the Northern Hemisphere, hold the watch flat and point the hour hand at the sun. Bisect the angle between the hour hand and the 12-o’clock mark to get the north-south line. If there is any doubt as to which end of the line is north, remember that the sun rises in the east, sets in the west, and is due south at noon. The sun is in the east before noon and in the west after noon. NOTE: If your watch is set on daylight savings time, use the midway point between the hour hand and 1 o’clock to determine the north-south line.
In the Southern Hemisphere, point the watch’s 12-o’clock mark toward the sun; a midpoint halfway between 12 and the hour hand will give you the north-south line.
Alternate watch method
Another method is called the 24-hour clock method. It requires a bit of math. Take the local military time and divide it by two. Imagine this result to now represent the hour hand. In the Northern Hemisphere, point this resulting hour hand at the sun, and the 12 o’clock mark will point north.
For example, it is 1400 hours. Divide 1400 by two and the answer is 700, which will represent the hour. Holding the watch horizontal, point the 7 at the sun and 12 will point north. In the Southern Hemisphere, point the 12 at the sun, and the resulting “hour” from the division will point south.