7-21. Using the sun and shadows. The earth’s relationship to the sun can help you to determine direction on earth. The sun always rises in the east and sets in the west, but not exactly due east or due west. There is also some seasonal variation. Shadows will move in the opposite direction of the sun. In the Northern Hemisphere, they will move from west to east, and will point north at noon. In the Southern Hemisphere, shadows will indicate south at noon. With practice, you can use shadows to determine both direction and time of day.
Shadow Tip Method
7-22. The shadow-tip method is ineffective for use beyond 66’/2° latitude in either hemisphere due to the position of the sun above the horizon. Whether the sun is north or south of an isolated person at mid- day depends on the latitude. North of 23.4°N, the sun is always due south at local noon and the shadow points north. South of 23.4°S, the sun is always due north at local noon and the shadow points south. In the tropics, the sun can be either north or south at noon, depending on the date and location, but the shadow progresses to the east regardless of the date. This method consists of four basic steps (see figure 7-8):
- Step 1. Place a stick or branch into the ground at a level spot where a distinct shadow will be cast. Mark the shadow tip with a stone, twig, or other means. This first shadow mark is always the West direction. (Note. The sun “rises in the east and sets in the west” (but rarely due east and due west). The shadow tip moves in just the opposite direction. Therefore, the first shadow-tip mark is always in the west direction, and the second mark in the east direction, any place on earth.
- Step 2. Wait 10 to 15 minutes until the shadow tip moves a few inches. Mark the new position of the shadow tip in the same way as the first.
- Step 3. Draw a straight line through the two marks to obtain an approximate east-west line.
- Step 4. Standing with the first mark (west) to your left, the other directions are simple; north is to the front, east is to the right, and south is to the rear.
Note: A line drawn at right angles to the east-west line at any point forms the same approximate north-south line, which will help orient a person to the same cardinal directions.
7-23. Inclining the stick to obtain a more convenient shadow does not impair the accuracy of the shadow-tip method. Therefore, an isolated person on sloping ground or in highly vegetated terrain need not waste valuable time looking for a large, level area. A flat spot, the size of the hand, is all that is necessary for shadow-tip markings and the base of the stick can be either above, below, or to one side of it.
7-24. In addition, any stationary object (the end of a tree limb or the notch where branches are jointed) serves just as well as an implanted stick because only the shadow tip is marked. The shadow-tip method can also be used to find the approximate time of day as follows:
- Move the stick to the intersection of the east-west line and the north-south line, and set it vertically in the ground.
- The west part of the east-west line indicates the time is 0600 and the east part is 1800.
- The north-south line now becomes the noon line. The shadow of the stick is the hour hand in the shadow clock and with it – estimate time by using the noon line and the six o’clock line as the guides. Depending on the location and the season, the shadow may move either clockwise or counterclockwise, but this does not alter the manner of reading the shadow clock.
- The shadow clock is not a timepiece in the ordinary sense. It always reads 0600 at sunrise and 1800 at sunset. However, it does provide a satisfactory means of telling time in the absence of properly set watches. Being able to establish the time of day is important for such purposes as keeping a rendezvous, prearranged concerted action by separated persons or groups, and estimating the remaining duration of daylight. Shadow-clock time is closest to conventional clock time at midday, but the spacing of the other hours, compared to conventional time, varies somewhat with the locality and date.
Equal-Shadow Method
7-25. This method determines direction and is a variation of the shadow-tip method, (see figure 7-9). It is more accurate and may be used at all latitudes less than 66° at all times of the year. It consists of the following four steps:
- Step 1. Place a stick or branch into the ground vertically at a level spot where a shadow at least 12 inches long will be cast. Mark the shadow tip with a stone, twig, or other means. This must be done 5 to 10 minutes before noon (when the sun is at its highest point [zenith]).
- Step 2. Trace an arc using the shadow as the radius and the base of the stick as the center. A piece of string, shoelace, or a second stick may be used to do this.
- Step 3. As noon approaches, the shadow becomes shorter. After noon, the shadow lengthens until it crosses the arc. Mark the spot as soon as the shadow tip touches the arc a second time.
- Step 4. Draw a straight line through the two marks to obtain an east-west line.
Watch Method
7-26. This method requires the use of a common analog watch—one that has hands. Use of this type of watch will enable the isolated person to determine the approximate true north and true south (see figure 7-10 on page 7-12). In the North Temperate Zone only, the hour hand is pointed toward the sun. A south line can be found midway between the hour hand and 1200 hours, standard time. If on daylight savings time, the north-south line is found between the hour hand and 1300 hours. If there is any doubt as to which end of the line is north, remember that the sun is in the east before noon and in the west after noon.
7-27. The watch may also be used to determine direction in the South Temperate Zone. However, the method is different. The 1200-hour dial is pointed toward the sun, and halfway between 1200 hours and the hour hand will be a north line. If on daylight savings time, the north line lies midway between the hour hand and 1300 hours.
7-28. The watch method can be inaccurate, especially in the lower latitudes, and may cause circling. To avoid this, make a shadow clock and set the watch to the time indicated. After movement for an hour, take another shadow-clock reading and reset the watch if necessary.
7-29. If you only have a digital watch, draw a clock face on a circle of paper with the correct time on it and use it to determine your direction at that time. You may also choose to draw a clock face on the ground or lay your watch on the ground for a more accurate reading.
24-Hour Clock Method
7-30. To utilize this method, take the local military time and divide it by two. In the Northern Hemisphere, point the hour hand at the sun, and the 12 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.
Using the Moon
7-31. Since the moon has no light of its own, we can only see it when it reflects the sun’s light. As it orbits the earth on its 28-day circuit, the shape of the reflected light varies according to its position. We say there is a new moon or no moon when it is on the opposite side of the earth from the sun. Then, as it moves away from the earth’s shadow, it begins to reflect light from its right side and waxes to become a full moon before waning, or losing shape, to appear as a sliver on the left side. If the moon rises before the sun has set, the illuminated side will be the west. If the moon rises after midnight, the illuminated side will be the east. This obvious discovery provides a rough east-west reference during the night.
Using the Stars
7-32. The location of the isolated person in the Northern or Southern Hemisphere determines which constellation is used to determine north or south direction. Each sky is explained as follows:
Northern Sky
7-33. The main constellations to learn are Ursa Major, also known as the Big Dipper, the Little Dipper, and Cassiopeia, also known as the Lazy W. Use them to locate Polaris, also known as the polestar or the North Star. Polaris is considered to remain stationary, as it rotates only 1.08 degrees around the northern celestial pole. The North Star is the last star of the Little Dipper’s handle and can be confused with the Big Dipper. However, the Little Dipper is made up of seven rather dim stars and is not easily seen unless far away from any town or city lights. Confusion can be prevented by using both the Big Dipper and Cassiopeia together. The Big Dipper and Cassiopeia are generally opposite each other and rotate counterclockwise around Polaris, with Polaris in the center. The Big Dipper is a seven-star constellation in the shape of a dipper.
Stars
7-34. Forming the outer lip of this dipper are the “pointer stars” because they point to the North Star. Mentally draw a line from the outer bottom star to the outer top star of the Big Dipper’s bucket. Extend this line about five times the distance between the pointer stars. The North Star will be located along this line.
7-35. The North Star can always be found at the same approximate vertical angle above the horizon as the northern line of latitude of the current location. For example, if at 35 degrees north latitude, Polaris will be easier to find if they scan the sky at 35 degrees off the horizon. This will help to lessen the area of the sky in which to locate the Big Dipper, Cassiopeia, and the North Star. Cassiopeia or the Lazy W has five stars that form a shape like a “W.” One side of the “W” appears flattened or “lazy.”
7-36. The North Star can be found by bisecting the angle formed on the lazy side. Extend this line about five times the distance between the bottom of the “W” and the top. The North Star is located between Cassiopeia and Ursa Major (the Big Dipper). After locating the North Star, locate the North Pole or true north by drawing an imaginary line directly to the earth (see figure 7-11).
Southern Sky
7-37. There is no single star bright enough, which can be seen near the south celestial pole. Therefore, use a constellation known as the Southern Cross. You can use it as a signpost to the south. The Southern Cross or Crux has five stars. Its four brightest stars form a cross. The two stars that make up the cross’s long axis are used as a guideline.
7-38. To determine south, imagine a distance four and one-half to five times the distance between these stars and the horizon. The pointer stars to the left of the Southern Cross serve two purposes. First, they provide an additional cue toward south by imagining a line from the stars toward the ground. Second, the pointer stars help accurately identify the true Southern Cross from the False Cross. The intersection of the Southern Cross and the two pointer stars is very dark and devoid of stars. This area is called the coal sac. Look down to the horizon from this imaginary point and select a landmark to steer by. In a static survival situation, isolated persons can fix this location in daylight by driving stakes in the ground at night to point the way (see figure 7-12).
7-39. Depending on the star selected for navigation, azimuth checks are necessary. A star near the north horizon serves for about half an hour. When moving south, azimuth checks should be made every 15 minutes. When moving east or west, the difficulty of staying on azimuth is caused more by the likelihood of the star climbing too high in the sky or losing itself behind the western horizon than it is by the star changing direction angle. When this happens, it is necessary to change to another guide star.
Improvised Compass
7-40. Improvised compasses can be constructed using a piece of ferrous metal, either needle-shaped or a flat double-edged razor blade, and a piece of thread or long hair from which to suspend it. Magnetize or polarize the metal by slowly stroking it in one direction on a piece of silk or carefully through your hair using deliberate strokes. You can also polarize the metal by stroking it repeatedly at one end with a magnet. Always stroke in one direction only. Suspend the needle or blade with the hair. The needle will gradually align itself in the north-south direction.
7-41. If you have a battery and some electric wire, you can polarize the metal electrically. The wire should be insulated. If it is not insulated, wrap the metal object in a single, thin strip of paper or a leaf to prevent contact. The battery must be a minimum of 2 volts. Form a coil with the electric wire and touch its ends to the battery’s terminals. Repeatedly insert one end of the metal object in and out of the coil. The needle will become an electromagnet. When suspended from a piece of nonmetallic string or floated on a small piece of wood, cork, or a leaf in water, it will align itself with a north-south line.
7-42. A more elaborate improvised compass can be constructed using a sewing needle or thin metallic object, a nonmetallic container (for example, the cut-off bottom of a plastic container or soft drink bottle), and the silver tip from a pen. To construct this compass, take an ordinary sewing needle and break in half. One half will form the direction pointer and the other will act as the pivot point. Push the portion used as the pivot point through the bottom center of the container; this portion should be flush on the bottom and not interfere with the lid. Attach the center of the other portion (the pointer) of the needle on the pen’s silver tip using glue, tree sap, or melted plastic. Magnetize one end of the pointer and rest it on the pivot point.
Floating Needle or Leaf Compass
7-43. Magnetize a metal sewing needle by stroking it in one direction with a piece of silk or by running it across a small magnet. Oil the needle by passing it through your hair. Place the needle gently on the water surface. The oil on the needle will cause the needle to float on the water surface. The needle will gradually align itself in the north-south direction. As an alternative, the magnetized needle is placed on a small piece of cork, leaf, duct tape, etc. The needle will float and will gradually align itself in the north-south direction.
Other Means of Determining Direction
7-44. Moss growing on a tree cannot be relied on to indicate north because moss grows completely around some trees. Actually, growth is lusher on the south-facing side of trees in the northern hemisphere and on the north-facing side of trees in the southern hemisphere. If there are several felled trees around for comparison, look at the stumps. Growth is more vigorous on the side toward the equator, and the tree growth rings will be more widely spaced. Conversely, the tree growth rings will be closer together on the side toward the poles.
7-45. Wind direction may be helpful in some instances where there are prevailing directions and the isolated persons know what they are.
7-46. Recognizing the differences between vegetation and moisture patterns on north- and south-facing slopes can aid in determining direction. In the northern hemisphere, north-facing slopes receive less sun than south-facing slopes and are therefore cooler and damper. In the summer, north-facing slopes retain patches of snow. In the winter, trees and open areas on south-facing slopes and the southern side of boulders and large rocks are the first to lose their snow. The ground snowpack is also shallower due to the warming effects of the sun. In the southern hemisphere, all of these effects will be the opposite.
Next Page : Navigation Methods