The Bushwalker's Guide to the Galaxy

or

Improvised Navigation - How to navigate the Surface of the Earth with less than a GPS or Compass

by Alan Sheehan B.E.

(with apologies to Douglas Adams - author of "The Hitch-Hikers Guide to the Galaxy")

Don't Panic

Disclaimers

The techniques included in this document require practical skills, knowledge and application. The author accepts no responsibility for the application (correct or otherwise) of these techniques, or the results of such application. While every effort has been made to ensure the information is correct, errors may exist. The author in no way encourages the use of Improvised Navigation Techniques as a substitute for modern navigation methods, techniques, and equipment. In the interest of Preventive Search and Rescue, the author encourages the use and practice of all navigational techniques available.

Sorry, Ford, Arthur, Trillian, Zaphod and Slartibartfast have nothing to do with this... and there are certainly no electronic thumbs here!

What's here....?

Improvised Navigation is being able to find your way without a compass, GPS or other sophisticated navigational device. Improvised navigation techniques are based on methods used by mankind for centuries prior to the invention of the compass.

Why Learn Improvised Navigation Methods?

Improvised Navigation methods are just another set of navigation tools. They are based on observation and awareness of our surroundings - our world. When Improvised Navigation methods are learned, reliance on compasses and GPS's is reduced. Of course it is still wise to use them, but when they fail, someone who can navigate without them is less likely to feel stranded or "lost". Improvised navigation techniques can and are used to check modern navigation methods, for example, to check a compass bearing for the affects of a magnetic anomaly. A good navigator always checks - preferably using another method!

Learning Improvised Navigation Techniques puts one more in touch with their environment, and far more capable and less likely to become a search subject. Of course, for this to be the case, I advocate using all navigation techniques you have available - don't toss the compass and GPS!

Improvised navigation techniques are good pose value around the campfire too!

Awareness

Improvised Navigation is all about awareness - of our surroundings: our world. We haven't lost all our "mental arithmetic" navigation skills. We are aware that the sun and moon rise (roughly) in the east and set (roughly) in the west. We develop a rough idea of where the sun should be in the sky at a particular time of the day. These signals give us our initial "sense of direction". We often almost subliminally use shadows, and we use prominent landmarks and local knowledge of our surroundings as well to maintain our "sense of direction".

Disorientation occurs when we take away the familiar landmarks and terrain, and natural direction indicators like the sun. Cavers cannot use distant landmarks, or the sun or moon. They rely heavily on learning the cave system (local knowledge) and/or mapping and compass navigation. Without a compass, the "sense of direction" can get way out of whack underground! Heavily overcast days above ground can produce similar disorientation in unfamiliar surroundings.

What people are least aware of these days, are the "long hand" navigation methods. Things like knowing what directions certain stars rise and set at (traditionally a popular method, so it seems), knowing how to find directions from various groups of stars anywhere in the sky, even just knowing how to measure angles. People also have little idea about how accurate various methods are.

Angles

Navigation is all about angles.... well, OK... distances too. The convention normally used is to measure all directions from North (such is the impact the compass has had on navigation!). The old Compass Points (NE, NNE, etc) are seldom used these days, especially for navigation, except to indicate a general or rough direction. Directions are described as angles (bearings) from North.

Some notes on Errors

In discussing the following methods of measuring angles and later when discussing directions, reference will be made to "errors". Errors are not mistakes. Errors are a measure of accuracy. Many of the methods discussed are very practical techniques. Like most things practical, there is a component of error which is a result of how well the technique is performed (Personal Error), and there is a component or error that is inherent to the method (Inherent Error). No matter how well a technique is performed, the accuracy can never be better than the inherent error in the method. Unless noted otherwise, all references to errors will mean the inherent error in the method: personal errors (due to how well the technique is performed) are added on top.

Compass

A compass is, of course, designed to measure angles and directions. Compasses available to most people are magnetic, so directions are measured relative to magnetic north. Gyroscopic compasses also exist. As a compass is a specific navigation tool we will not consider it further in the context of improvised navigation.

Several methods can be used to make improvised compasses, however.

The Suspended Needle

A magnetised needle (nail or wire, etc) can be suspended from a thread. Provided it is balanced and not influenced by the breeze, the needle will indicate magnetic North. Some further information (know the polarity of the needle, or see the general direction of the sun, for example) will be required to determine North from South.

A similar arrangement can be effected by supporting the needle in a cork floating on water, or on a piece of paper supported by surface tension on water.

Other Angle Measuring Devices

Other devices like protractors, theodolites, clinometers, etc will not be considered here because they are designed to measure angles and so do not represent an improvised technique.

Watch

The analogue watch is a convenient measure or indicator of angles. Each hour mark on the face of the watch represents 30 degrees from the centre, while each minute mark represents 6 degrees from the centre.

Handspan

The hand is probably the earliest used and most common angle measuring tool available to man: nearly everybody has two!

The trick to using a handspan to measure angles is consistency. The hand span must be the same width, and it must be the same distance from the eye each time it is used to measure an angle. As the hand is brought closer to the eye, the angle it subtends at the eye increases.

To keep this method consistent, always stretch the hand as wide as it can go, and extend the arm as far as it will go. The hand span is then measured from the tip of the thumb to the tip of the little finger. Most people will have a hand span of about 20 degrees. People with small hands may have a handspan of 15 degrees or so, while people with big hands may be able to stretch to 25 degrees.

Calibration

To use the handspan, one needs to know the angle their hand subtends at the eye. This is worked out by counting the number of handspans in a full circle. This is done by holding the hand fully spread at arms length with the tips of the thumb and little finger horizontal. Aim the tip of the thumb at a feature against the background, and notice where the tip of the little finger is. Now place the thumb where the little finger was and notice the new position for the little finger. In this way, step around in a full circle. Using a background that is distant (eg outdoors) will decrease errors as a result of moving the body to turn around. Since there are 360 degrees in a circle, divide 360 by the number of handspans, and the result will be your personal handspan in degrees.

Generally, the width across the knuckles of a clenched fist at arms length will be half the angle of a handspan, while the angle between the knuckles (include the thumb beside the fist) is a fifth of that again. These methods can be used to estimate angles less than a handspan. Of course, angles larger than a handspan can be estimated by adding handspans, and fistspans (etc), in the same way as the handspans were counted to determine the handspan angle.

Astronomers have used (and still do) this technique for centuries to estimate angles between stars and celestial objects and, more recently, just to find their way around the sky quickly and conveniently.

Armspan

This method is a simple method for determining a rightangle from a baseline such as a wall or fence.

Stand with arms outstretched to each side along the baseline. If the baseline is a fence or wall, lean against the structure and settle into a position where pressure from the structure is the same on both sides of the body. Now bring both hands together with the arms outstretched. The line from your nose, to the join between the hands when the finger tips are level should be at 90 degrees to the baseline.

A Piece of String?

Another method of measuring angles is to use a piece of string. Rope, cord or shoe lace will do. What you want to end up with is a continuous loop with twelve knots or marks equally spaced around it. Why twelve? Because Pythagoras liked the number twelve... You will remember from high school maths that a triangle with sides of 3 units, 4 units and 5 units is a right angled triangle. 3+4+5 = 12. So straight away with our piece of string we can make and measure a rightangle (90 degrees). We can also make a triangle with each side 4 units long - an equilateral triangle. So we also have 60 degree angles. Now from one point of the equilateral triangle to the mid point of the opposite side will give us two 30 degree angles, while the other two knots on that side will provide near enough to 15 degrees. There are all sorts of combinations possible.

Measuring Time

Angles can also be used to measure time. As the earth rotates 15 degrees every hour, the height of the sun above the horizon can be used to determine the time since sunrise, or more importantly, the time till sunset. This can be applied to the moon, or any celestial body which is near the celestial equator. Stars away from the equator do not appear to move as quickly, and in fact may not even set, as their motion around the earth is not along a "great circle". For example, a person with a handspan of 15 degrees knows that when the sun is one handspan from the horizon, there is only an hour till sunset. It is worth noting here that, twilight ends about 25 minutes or less after sunset.

Measuring Slopes

Measuring angles is also important for measuring the slope of ground. This can be important to cross country navigators such as bushwalkers, to help confirm positions, or to four wheel drivers to make sure the limitations of their vehicles are not exceeded.

Estimating Angles

The sun and moon each subtend an angle of about 0.5 degree from the earth. Angles of about this size can be estimated by comparing with the apparent size of the sun or moon.

The Sun

The sun is very important to our "sense of direction", but that doesn't mean it is a good guide for navigation. Accurate direction finding from the sun is complex and depends on the time of day, the time of year (seasons) and the observer's latitude. To illustrate the problem consider these scenarios:

You are located on the equator. It is sunrise. It is the middle of the northern hemisphere summer (southern winter). The sun is rising in the East (from a "sense of direction" point of view) but the bearing to the sun will be about 23 degrees North of East (ie 67 degrees). This error, +/- 23 degrees is due to seasons. At the same time an observer above the Arctic Circle didn't even see the sun set to see it rise! This effect is a result of the observers latitude. The effect produces an additional error in the direction to the sun, which increases with increasing latitude.

Popularised methods of direction finding using the sun often fail to mention these sources of error, leaving people to think they only have their personal accuracy to worry about.

Using the Sun and a Watch

One of the popularly publicised methods of finding north during the day uses an analogue watch.

The method goes as follows for the southern hemisphere temperate zone:

  1. Align the 12 on the watch face with the sun.
  2. Mentally halve the angle between the hour hand and the 12. This direction is "North".

In the northern hemisphere temperate zone the method is:

  1. Align the hour hand with the sun.
  2. Mentally halve the angle between the hour hand and the 12. This direction is "South".

The following points are relevant to this method.

Firstly, the watch must be working, and set to standard time not daylight saving time. Daylight saving time will simply result in a 15 degree error to the east.

Secondly, a digital watch can be used provided you have adequate knowledge of how an analogue one works and can draw the watch face in the dirt or somewhere. A bit less accurate again, but...

This method is really quite rough: errors up to 25 or 30 degrees or more are possible unless you understand the movements of the sun and can compensate for the errors. It is most accurate during the middle of the day. This method should be abandoned for the previous method during early morning and late afternoon.

This method also loses accuracy and reliability as your latitude approaches the tropics, and this method is not recommended for use there. Knowledge is also required of what times of the year the sun is south during the middle of the day. This requires knowledge of your latitude and what time of year the sun moves directly overhead.

The Middle of the Day

South of the tropics, the sun will be true North (plus or minus 7.5 degrees) at midday (12:00pm standard time). Vice versa for observers North of the tropics. The reason for the error of plus or minus 7.5 degrees is because a time zone is 15 degrees wide on the face of the earth. So civilian "midday" can be up to half an hour either side of true, or celestial, midday.

In the tropics the sun could be north, south or directly overhead, which is not all that helpful for year round rules on improvised navigation.

Shadows

Another method popularised in the survival manuals, is to place a stick in the ground before mid day and mark the position and length of its shadow. Periodically plot the length of the end of the shadow till it is at a minimum, then continue for a similar amount of time afterwards. The shadow is at its minimum length at midday. The line through the tip of the shadow, sometime before midday, and the tip of the shadow the same time after midday will point West-East. The same time each side of midday is important because the tip of the shadow will describe a curve on the ground - not a straight East-West line.

If an accurate watch (ie to local time) is available, the stick used to generate the shadow need not be vertical, simply plot the positions of the shadow tips the same time each side of noon. Without the watch, it is important to get the tip of the stick vertically over the base so that shadow lengths can be used to determine equal time before and after midday.

Both these methods are reasonably accurate, but are limited in that they can only be used once per day! Using a vertical stick and equal shadow lengths has no inherent error, but may be subject to significant personal error (how vertical stick is, measuring shadow lengths, etc). Using a watch is subject to an inherent error due to position within a time zone (+/- 30 minutes), however, the effect of this on the accuracy of the direction determined depends on latitude, and the length of time each side of midday used. Generally, using a watch will give acceptably small errors if used for at least one to two hours each side of midday. The shadow stick method will work anywhere in the world but takes time to do. These methods are most useful if applied at a location where good visibility of the horizon is possible so that a prominent landmark can be used for guidance once the sun is no longer usable.

The Moon

The moon is advocated by some references as being suitable for improvised navigation. It is, but only in a similar way to the sun. It is a better "sense of direction" indicator than a reliably accurate direction indicator.

The methods generally described for navigation by the moon are the directions of rise and set; and direction indicated by the phase of the moon. The shadow method used to navigate by the sun can also be adapted.

The moon's orbit is tilted about 5 degrees from the ecliptic (the orbit of the earth around the sun, or more correctly the apparent path of the sun across the sky). This means the rise and set directions for the moon can be up to 28.5 degrees either side of true East/West (compared with 23.5 degrees for the sun). Of course, the error due to latitude is not included in that! (Because of precession, the angle of the moon's orbit to the earth's equator actually changes from about 18.5 degrees to 28.5 degrees over a period of several years).

So, you see the moon is actually a pretty inaccurate indicator of direction.

The one improvised method, that is accurate for navigation by the moon is the shadow stick method. However, as the moon is at its zenith (highest point in the sky) at different times from day to day, it is important to plot the points when the shadow is the same length each side of the zenith. A line from the first point to the second point indicates East. This method is most practical on clear moon lit nights in order to get a distinguishable shadow. The stick used to generate the shadow must be vertical for this method to be valid.

Normally the moon is most useful as a rough "sense of direction" indicator. It rises nominally in the East, and sets roughly in the West. If the moon is following the sun across the sky (ie visible early evening) the illuminated side of the moon is very roughly West. Likewise, if the moon leads the sun across the sky (ie doesn't rise till after sunset), then the illuminated side is roughly East. At least one reference I have seen suggests this navigation by the phase of the moon is accurate, but it is not. It is subject to errors due to the seasons, the inclination of the moon's orbit, and the observer's latitude.

The Stars

Most people know little about finding directions from the stars. In fact, most people know little about the stars at all! This wasn't always the case. While ancient man didn't know how far away they were or how hot they were, he knew them and their patterns intimately.

These days people don't give the sky much thought, and we live in places we like to pollute with bright lights and smog, washing the colour and brilliance out of the stars. The average twentieth century citizen of any modernised country is magnitudes more ignorant of the stars than in generations before.

Finding directions from the stars is far more accurate than using the sun or the moon. The stars require no seasonal correction factors like the sun does to accurately determine directions.

The first step to navigating by the stars is to determine a reference direction. We have four methods to choose from.

  1. The North Celestial Pole (NCP) or South Celestial Pole (SCP) can be found by measurement from recognised star patterns. True North or True South is the point on the horizon directly below the respective Celestial Pole. Only a few popular examples of these method are shown below. The possible options to navigate this way are only limited by familiarity with the sky.
  2. East or West can be found directly from bright stars near the Celestial Equator as they rise and set.
  3. The directions of rise and set of bright stars (away from the Celestial Equator) can be learned and used directly. Unfortunately these directions are affected by latitude. Traditionally this method was very popular before the invention of compasses. More information is available:
  4. Observing the Apparent Motion of the stars.

Ursa Minor, Polaris and Ursa Major

Of course, occupants of the Northern Hemisphere are more than likely familiar with Polaris (alpha Ursae Minoris) - the Pole Star. Polaris is within 1 degree of the North Celestial Pole (NCP) and is a very convenient (and accurate) indicator of North. True North is within 1 degree of the point on the horizon directly below Polaris.

Alpha and Beta Ursae Majoris (Dubhe and Merak) are commonly known as the pointers on the Northern Hemisphere as they point to Polaris (and the NCP). From Merak extend a line through Dubhe for 30 degrees from the midpoint between Dubhe and Merak.

Southern Cross, Alpha and Beta Centauri, and Achernar

The Southern Cross (Crux) is probably the best known constellation in the southern hemisphere. It is highest in the evening sky from March to September. Achernar (Alpha Eridani) is highest in the evening sky from October to March.

Several methods and variations are possible to find South from the Southern Cross. The star Achernar is the first bright star found by extending the foot of the Southern Cross. It is about 60 degrees away from the Southern Cross. Beta Centauri (Hadar or Agena) is the closest of the two pointers to the Southern Cross.

The first method locates south as half way between Beta Centauri (Hadar) and Achernar.

The second method is useful when Achernar cannot be seen. In this case, extend the long axis of the Southern Cross 4.5 times its length to find south. A variation on this is to project the axis of the cross 30 degrees from the centre of the cross (this is easier using the handspan method and has an inherent error of less than 2 degrees!).

A third method is possible when only Alpha (Rigel Kentaurus) and Beta (Hadar) Centauri are visible. Project a line from Rigel Kentaurus (alpha Centauri) 30 degrees perpendicular to the line through the two stars.

Orion

Orion is well known world wide. It is visible in the evening sky from November to May.

The belt and sword of Orion is otherwise known as "The Pot" due to its resemblance to a saucepan. Mintaka is the star of Orions belt furthest from the sword.It is within 1 degree of the celestial equator, so it rises and sets due East and West respectively.

When it is directly overhead, the handle of the pot (Orion's sword) points north/south.

North or South can be found from the handle of the pot when it is not directly overhead as follows. Project a line parallel to the sword of Orion for 90 degrees from Mintaka. On the sword side of Mintaka this would locate the South Celestial Pole, in the other direction, the North Celestial Pole.

Scorpius and Ara

Scorpius is visible in the evening sky from May to November. Just to south of the tail of Scorpius is a relatively insignificant constellation - Ara. Once learned though, it does have a distincyive shape and can be used to find the SCP.

From the mid-point between Theta and Eta Scorpii extend a line 45 degrees through Beta Arae to find the SCP.

Leo

Leo is visible in the evening sky from February to July. Two methods can be used to find the NCP using Leo. The NCP is 80 degrees from Alpha Leonis (Regulus) through Eta Leonis. The other method is to extend a line from Theta Leonis through Delta Leonis (Zosma): the NCP is 70 degrees further along this line.

Observing the Apparent Motion of the Stars

The best way to observe the apparent motion of the stars is to use a fixed sight, and keep the eye very still. The best way to keep the eye still is to lay down on the back in a comfortable position, with the head comfortably supported. The sight could be a stiff stick supported rigidly so one end is overhead, or a protrusion of rock from an overhead cliff is also suitable. Trees and branches make poor sights as they move and sway in the slightest breeze.

It takes only a few minutes to observe the direction of motion of the stars. Note carefully the position of a star very near the sight. Wait a couple of minutes (or until the motion is apparent) to observe the motion of the star, but DO NOT MOVE THE HEAD! It is worth mentioning here that stars move very slowly near the North or South Celestial Poles.

The references I have seen referring to this method advocate finding direction from the apparent motion itself. In reality, this is only practical again as a "sense of direction" aid. Also, it is complicated by the observer's latitude, and is subject to errors if a star is picked that is low in the sky. For example, if the star moves horizontally from right to left it indicates you are facing North, however, if you are in the Southern Hemisphere, and the star is low in the sky, it could mean you are facing South! (ie the star is below the SCP). To avoid this 180 degree error, always pick a star high in the sky (greater than your latitude above the horizon).

For reasonable accuracy, the best and simplest method is to position the eye directly beneath the sight. The direction the star nearest the sight is moving towards, is West.

If it is impractical to sight a star directly overhead, the following method may be suitable. Observe the motions of stars near the horizon roughly 90 degrees apart. Where the stars either move very slowly, or move parallel to the horizon may be either north or south. Where the stars rise steeply from the horizon is obviously east, and where they set steeply is west. The angle of movement for stars at east or west equals 90 degrees minus the observer's latitude. For example, at 35 degrees South (or North), a star at the east will rise at an angle of 55 degrees from the horizon. The angle will always "lean" towards the equator. This is a very rough method, and will provide "sense of direction" information only, not accurate directions. It is also of diminishing value as latitude increases - at the poles, the stars on the horizon simply follow the horizon!

Local Knowledge

Local knowledge cannot be beaten when it comes to improvised navigation. Familiar Landmarks help the observer to assess directions and location. When landmarks are not visible, knowledge of the area comes into play, for example, the general direction of flow of rivers, or the fact that termites build mounds aligned N-S in northern Australia to help control internal temperature. Some flowers move to follow the sun, even when the sun is obscured behind heavy cloud. Wind directions are fickle and usually of little value for navigation: they change with time and wind directions in a gully are likely to be different on the ridge top. The direction of movement of weather systems gives a little more reliable information, however.

Where to find out more?

Death before Disorientation!

Don't Panic

 

The Bushwalker's Guide to the Galaxy / Alan Sheehan / als@mail.ix.net.au / revised August 16, 1997