Thursday, 30 October 2014

Direction Finding by the Moon.


                The other night I was looking at the crescent moon. Many readers of this blog are doubtless familiar with how to find direction from the moon, but some will not be, so indulge me for a moment. By drawing an imaginary line between the horns of the crescent and extending it down to the horizon the approximate position of south can be estimated if in the northern hemisphere, or north if you are in the southern hemisphere.

 
                Idly I wondered if the angle of this line had any relationship to the latitude of the observer. I recalled there was something about navigating by moon in the Japanese Manual of Night Movements.

“Although it is difficult to determine direction by the position of the moon, the latter has the advantage of being recognizable even on nights when all the stars cannot be seen. The moon crosses the meridian about noon on the first lunar day, and it moves about fifty minutes behind the sun every day. Therefore, if the age of the moon be known, the approximate passing of the meridian can be easily computed. Its approximate age can be computed from the shape of its bright portion.”

Not really that helpful! Something may have been lost in the translation. Most websites I looked at had no answer but eventually I found this interesting paper and found the answer is “no”.
I later confirmed my latitude was 51 degrees so an angle of either 51 or 39 would have been expected if the hypothesis had been correct. The range of angles the terminator can be at as it approaches and passes meridian will vary with latitude, however, but this has very little application to practical emergency navigation.




 

An alternate method for direction finding by the moon involves remembering that the sun sets in the west and rises in the east. If the moon is up in the early part of the night, or in the evening before the sun has gone down the illuminated side will be the western. If the moon is observed in the latter part of the night or in the morning then the eastern side will be illuminated. In this context “latter” and “early part” of the night are defined in relation to the median point of the night, also known as Solar Midnight. In other words, the middle of the period of darkness rather than the chronological “midnight”, 12:00am or 0000hrs on the clock. This is more of a secondary method since if you can see the light and dark parts of the moon you can use the terminator method to find north or south. I suppose you could make a crude estimate of the time by establishing where south or north is located and then observing which side of the moon was illuminated.


You can also estimate direction from the moon using the shadow tip method. This is often illustrated using the sun but the principle is exactly the same using the moon. Place an object such as a stick in the ground so that it casts a shadow. Mark the tip of the shadow. Wait for at least fifteen minutes so the shadow has time to move. Mark the tip of the shadow’s new position. A line drawn between these two points will run east-west. The first point you marked will always be west, the second east. Easy for me to remember since my name is “West” so “West comes first!”. Both the moon and the sun move from east to west and in the northern hemisphere they are always in the southern half of the sky so shadows cast have varying degrees of northward orientation. A line perpendicular to the east-west line will be north-south and the shadow will be in the direction of the pole of the hemisphere that you are in.

The advantage of the shadow tip method is that you can use it when there is a full moon and you could not use the terminator method. In the daytime you can use the shadow tip method when the exact position of the sun cannot be seen because of clouds, so long as there is enough light to throw a shadow.

 The Books
http://www.angelfire.com/art/enchanter/epsdbook.html

 

Friday, 24 October 2014

Christmas Creep - it begins again, already!


                A recent topic of some discussion on the internet was the Christmas tree in Paris that is widely regarded as looking like a butt plug. Most of us, however, missed the real issue, which is why is a Christmas tree of any form is being erected in early October?
 
 

                I was in a restaurant with my girlfriend this Sunday. They had a Christmas tree of beer cans in the window. It was the twelfth of October! Last year I wrote on the topic of Christmas Creep and predicted that it may start even earlier this year. Already a TV station boasts that they will be broadcasting 24 hour Christmas movies. I so hate being right!

Wednesday, 22 October 2014

Movement in Armour.


                A common piece of Victorian whimsy was that the knight in armour needed a crane to haul him up into his saddle. In reality a suit of plate armour might weigh around 20-25kgs. This is actually less weight than that of the equipment that a modern soldier or firefighter might carry. Certainly I have carried rucksacs of this weight when necessary. The weight of a suit of armour would have been better distributed than that of a modern pack.

            Many years ago I read about the feats of a knight called “Jean le Maingre” (ca. 1366–1421), aka “MarĂ©chal Boucicault”. Wearing armour he could climb up the underside of a ladder only using his hands.

“Boucicaut or Jean de Meingre marechal de France who commanded the vanguard of the French army at Azincourt in 1415 and was there made prisoner and died in England in 1421 used to go up on the lower side of a ladder leaning against a wall without touching it with his feet but only by jumping with both his hands together from one bar to the other and that he would do armed with a steel coat and having taken off the armour with one hand alone he could ascend several bars and these things are true and by many other hard exercises of such sort he so hardened his body that his equal was hardly to be found….

…….Boucicaut at one time used to accustom himself to leap in armour on the back of a horse and often he would walk or long distances to give him long breath and enable him to bear fatigue. He also used to strike for a long time with an axe heavy hammer to harden his arms and hands and to accustom himself to raise his arms readily. By following such exercises he strengthened his body so greatly that in his time there was no gentleman to compare with him. He could throw a somerset completely armed except his basnet and would dance when armed with a steel coat In full armour and without putting a foot in the stirrup he would jump on the back of a war horse. He would also jump from the ground astride on the shoulders of a big man or a tall horse without other help than a hold of the sleeve of a man's jerkin. Holding with one hand by the pommel of a saddle placed on a high horse and with the other grasping the mane a little below the ears he would from the ground jump through his arms to the other side of the horse and he would ascend between two side walls of plaster at the distance of a fathom from each other and by the force alone of his arms and legs without other aid without falling either going up or coming down."
Extracted from his Life pour servir a I Histoire de France

An introductory course of modern gymnastic exercises

 By George Roland

            Boucicaut was obviously an exceptional individual but it is evident that the wearing of armour was much less restrictive than many people assume. Most of us have seen medieval illustrations that show armoured fighters ascending ladders during an assault on castle walls. Illustrations also exist of knights mounting their horses without need for assistance.

            A friend of mine sent me this video which shows two re-enactors performing various movements in armour. Bear in mind that these gentlemen do not wear armour as often as a medieval fighter would have, yet still can move around freely.



            Here are some additional videos I found.





The Books
http://www.angelfire.com/art/enchanter/epsdbook.html