Pathfinding - finding declination and directions

[le Voyageur]

- To find the declination for your area, set the direction of travel on a compass to north, and take a bearing off of Polaris. The compass's needle will point to mag north, this is your declination.

 

- To orientate a map without a compass, the map can be held between the constellations of the Big Dipper and Cassiopeia.

 

- To orientate oneself at night without a compass, by "placing" one's hand on the Big Dipper and the other on Cassiopeia when they are at their 3 and 9 postion, you will be facing due north. When these constellations are "standing" on top of each other , you are facing due north.

 

- The winter constellation Orion, when setting, will give due west.

 

- The summer constellation Scropio, will give due south when the stars in the head stand stright up.

 

- If your compass has an inclinometer, by taking the "slope angle" of Polaris, you can get a rough latitude. A line of latitude drawn across the map will give a crude fix when it crosses any north/south landmark near your position (river, trail, ridge line, road, etc.).

 

- To find due south during the day, note and add sunrise and sunset times, then divide the sum by 2 (requires 24 hour time. This will give local apparent noon(LAN), also known as solar noon. The sun will be at it's zenith and bearing due south and headed west.

[morganfam7]

I was just told that the shadow part of a full moon - the valleys and canyons always points north while the bright half always points south. Is this true? I can't find anything about it in my books.

 

Thanks for the good information above! We need to work on our knowledge of the constellations. Sounds like a good topic for a month of troop meetings. Do you think finding certain constellations would be a great outside preopening activity?

 

Thanks,

 

Marcy

[le Voyageur]

To be honest, I've not heard of that one, and is, in my mind, ramped with misconceptions. Consider this, that the moon is the most evasive of all celestial bodies. It moves westward with the stars each day because of the earth's rotation, but it also slips eastward relative to stars because of its own orbital motion around the earth. Since the moon circles the earth once a month, it progresses through the stars at a rate of 360 degs. per (roughly) 30 days, or about 12 degs. per day. If the moon is next to the star Aldebaran on one night, on the next night it will be about 12 degs. to the east of Aldebaran (which is about half an outstretched hand's width at arm's length). If you have a watch and know solar time, the moon can be helpful on special occasions. When the moon is full, it behaves just like the sun, with solar noon (LAN) changed to "solar midnight," meaning LAN + 12 hours. For example, if I know the sun lies due south at 1330 hrs according to my watch, then a full moon that night will lie due south at 0130 hrs. But, the problem with this method is obvious, a full moon happens only once a month...

 

Aboutlearning constellations, this I feel should start at Tenderfoot, and be a part of the advancement requirements for the lower ranks. Just knowing how to locate the Big Dipper and Cassiopeia can oreintate one faster than a compass. Knowing how to use the Big Dipper to guide one self over to the North Star is an outdoor skill that should be in every scouts little bag of outdoor tricks. And it is here where a great preopening could be built around locating one's "guide star" and staying the course....since my own fascination for the stars comes from my Viking heritage I would tap into the old Norse legends as a program source...

 

 

 

 

[eisely]

Finding directions without a compass is a survival skill, not a practical skill that one will use in actually navigating under normal circumstances. The skills are taught under the First Class requirements. The only method I know of that works with the moon is the "shadow stick" method on p. 116 of the current handbook. This does not require a full moon. The method is taught for use with the sun, but shadows cast by the moon can be used as well.

 

All scouts should know how to locate the big dipper and polaris. Teaching these night navigation skills are a good night time activity, but they will not fill an entire evening.

[le Voyageur]

Wow! Do I disagree with celestial direction finding being useful only for a survival skill. Talk about bad advise. And the First Class requirements for this area is very weak and often glossed over,being taught by unit leaders working rote from a scout handbook filled with assumptions. I've also never seen an Eagle Scout, let alone a First Class scout who could find Polaris (when asked they will point to either Sirus or Jupiter, the reason is, is that they are taught that Polaris is the brightest object in the night sky).

The shadow stick method for the moon is a varition used for direction finding using the sun. Lets discuss some of the problems with these two methods....

The solar time method can produce serious errors if the sun is too high. We care about the height of the noon sun because this height, in effect, determines how fast the direction of the sun changes during the day. The sun always moves along it's invisible arc across the sky at a rate of 15 degs. per hour, but only when the noon sun is less than 45 degs high does the sun's bearing move along the horizon at a near-constant rate of 15 degs. per hour. In this conditions, it does so to a good approximation throughout the day, sunrise to sunset. And since the sun is on our meridian at LAN, if we know the time of LAN and the time of day, we can easily figure out the direction of the sun. From northern latitudes, at LAN the bearing of the sun is due south at 180 degs.. One hour after LAN the sun lies 15 degs. to the west of due south, bearing 195 degs. As a further example, suppose the time by your watch is 1120, and you know that LAN will be at 1340 according to your watch. Since it is 2 hours and 20 minutes (or 2.33 hours)before LAN, you know that the sun has to travel 2.33 x 15 degs, or 35 degs before reaching due south. In other words, at 1120 the bearing of the sun is 180 degs - 35 degs, or 145 degs. Strictly speaking, the solar time method yields only an approximation of the sun's direction. But whenever the noon sun is less than 45 degs. high, this approximation is a good one.

When the midnight moon height is below 45 degs, the solar time method can also be used two or three days before and after the full moon, without much loss in accuracy. When the moon is exactly full, the moon and sun are on opposite sides of the earth, which is why they pass us exactly 12 hours apart and why, to a good approximation, the full moon rises when the sun sets and the full moon sets when the sun rises. Each day following full moon, the moon moves 12 degs to the east of the sun. Since sun and moon move by us to the west, if the moon is now farther east of the sun, the time between the sun's passage and the moon's passage will be longer. The meridian passage of the moon is later than midnight on days following the full moon; at midnight, the moon has not yet reached the meridian. If you conclude from looking at the moon that it is one day after full moon, then at midnight the moon would be 12 degs to the east of your meridian. Two days after full moon, the moon would be 24 degs east at midnight. The same reasoning shows that on days before the full moon the time difference between sun and moon is less than 12 hours, so meridian passage of the moon occurs before midnight. If you conclude that it is two days before full moon, you can expect the bearing of the moon at midnight to be 24 degs to the west of your meridian - it passed you earlier than midnight. With the inherent uncertainties involved, we do not lose much accuracy by considering the 12 degs. daily motion of the moon to be about the same as the 15 degs. hourly rotation of the earth. And with this approximation, we can expand the last example to conclude that since the moon is 2x12 degs. farther along its orbit, it is about 2x15 degs, or 2 hours ahead of schedule on the meridian. So we expect the moon two days before full moon to be on the meridian 2 hours before midnight, at 2200 solar time. With this explanation behind us, we can restate the moon's behavior in a way that makes it easier to remember: The full moon is on the meridian at solar midnight. One day before full moon, the moon gets there one hour before midnight; one day after full moon, the moon is on the meridian one hour after midnight. Two days before, two hours before; two days after, two hours after.

 

[eisely]

I feel compelled to respond to le Voyageur for a variety of reasons.

 

His techniques and advice are interesting and no doubt useful in some situations. However, I think it would be a mistake to go into such detail with younger scouts. Let me explain.

 

1. The techniques he describes are well beyond the comprehension of new scouts who are trying to learn so many new skills at once. I daresay that most of the techniques are beyond the comprehension of many readers of these posts. That does not mean that adults and older scouts cannot be taught more advanced techniques. In teaching any skill you must keep in mind the target audience.

 

2. On any scout outing, be it canoe trip, long distance trek, or simple day hike, there should be at least two compasses available in case one becomes lost or damaged.

 

3. We teach scouts, if lost or separated from the group, to stop where they are, make themselves as comfortable as they can, and await rescue. I would not want to encourage scouts, or anybody, to attempt to navigate their way out of a "lost" situation without a compass. I would not want to build overconfidence in half learned and half remembered techniques.

 

4. Anyone who understands, remembers, and can apply all these techniques is unlikely ever to need them.

 

5. Few scout outings with younger scouts will involve cross country navigation. LNT principles urge us to use established trails.

 

Therefore I think the navigation skills that need to be emphasized are:

 

a. Basic map reading.

 

b. Relating what is on the map to what is on the ground. Not many adults are good at this either.

 

c. Orienting a map.

 

d. Understanding and being able to consider and apply declination.

 

e. Being able to apply simple methods of celestial navigation. With respect to this, we all should take the opportunity on camping trips when conditions are suitable, to refresh everyone's knowledge of the major constellations that can be used for direction finding. The point about boys, and leaders, not being able to locate Polaris is well taken.

 

I guess my reaction to all of le Voyageur's technical suggestions is that I prefer to keep things simple. To me, direction finding without a compass need be accurate to only a limited degree and enable me to roughly orient my map without a compass. If I can get the map oriented, I can then relate the map to what I see on the ground with sufficient accuracy.

 

Very few people really can relate what they see on the ground to what they see on the map. In the back country with few man made objects, this is not as straightforward as it might seem. This requires training in observation and interpretation. This is where I would put the emphasis.

 

It might be fun and interesting to attempt a long distance trek without a compass, but that is not something I would attempt with younger scouts, and that is the target audience we are talking about.

 

 

[le Voyageur]

E.

 

I fully agree with your observations in your last post. However, if you would reference my post that started this thread you will see that the techinues are simple, and easy to learn. These are what I teach to adults and older scouts and require knowing very little science. These techniques may not may be in the Scout handbook, but are the better method of meeting First Class Req. 1 ("Demonstrate how to find directions during the day and at night without using a compass"). My last two posts, explaining the science were written for adults, not for scouts.

[KoreaScouter]

Le Voyageur;

 

I envy your knowledge level in this subject; I'm an amateur. And, we have problems over here with washout from lights (very crowded urbanized country) and obscuration from pollution, etc.

 

We had a leader who moved last year who was an Air Force navigator -- knew all those stars as well as you seem to. He told a story of his B-52 crew over the Atlantic years ago, lost all their inertial navigation systems. He had to break out his sextant and shoot celestial through the porthole...got back to base right on the money and impressed the heck out of his crew mates.

 

Do you know of a concise, easy to use field guide on this, or is the Fieldbook the best thing out there?

[le Voyageur]

KS

 

This book may help

 

Land Navigation Handbook, the Sierra Club Guide to Map and Compass

 

W.S. Kals 1983

 

ISBN 0-87156-331-2

 

to locate a copy, do a ISBN search at

 

http://isbn.nu/

 

Question: Where in Korea are you at?? Did a det at Osan, many, many moons ago.

[eisely]

Another excellent reference is:

 

The Essential Wilderness Navigator (second edition)

 

by David Seidman & Paul Cleveland

 

ISBN 0-07-136110-3

 

This book begins at the beginning and includes many useful drawings to illustrate the techniques.

 

I envy the skill of the Air Force Navigator mentioned above. Fortunately in boy scouts we are not faced with those kinds of situations.

[KoreaScouter]

Gents;

 

Thanks for the quick comeback. LV, does the Sierra Club book deal with celestial, or just map/compass? I'm actually pretty squared away at map/compass; it's when I have to tip my head back and look up that I come up a little short...

 

I'm at Osan, fourth time...

[le Voyageur]

KS

 

This guide covers basic celestial navigation besides the map and compass.

 

Chapter 11 covers "Direction from the Sky: North of the Tropics"

 

and...

 

Chapter 12, the tropics and south of the tropics

 

One of the better chapters (Chap. 4) will take you step by step and show you how to convert countour lines into slope angles,average grade and foot, rise per mile, etc. using simple math. Info that makes the topo truly 3D in the field.

 

I'll look around for a few additional books on the subjects and post them for you since my interest is in ancient and primative sailing techniques.

 

On a side note when I'm teaching constellations, I find that introducing one or two at every campout is about the best way to keep from overwhelming folks.

Of the Constellations, Hercules is one of my favorites. Besides being useful for the telling of some great Greek myths, it offers the chance to introduce to the scouts one of the more interesting features of this constellation, being the mega giant star labeled alpha Ras Algeti. The size of this distant sun is huge...if we were able to fire a photon across the long axis of our solar system, transit at the speed of light would only take about 6 or so hours. Firing a photon across the diameter of this star would take 5.5 days! Well, I digress again....