Finding true North and time from the Sun with your fingers.

Finding true North and time from the Sun with your fingers.

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(Blog No. 149)

#find North, #finding North, #find true North, #North, #true North, #navigation, #find time, #time, #Sun, #fingers,

Finding true North and time from the Sun with your fingers.

There are times when you neither have your watch nor can use any magnetic compass in the location but you want to find out the North-South directions and the time. This method is useful for those such difficult situations. Those situations may arise if you get lost without having your watch while traveling or if you find yourself without your watch while traveling inside a bus or a train. The method from this article gives both the true North direction and the local time from the position of the Sun using only your fingers.

Required preparatory practices

1. Practice holding each of your hands in the three principal postures as illustrated in the following three figures.

Summer Solstice

Equinox

Winter Solstice

Figures: Hand postures for Summer Solstice, Equinox and Winter Solstice. Click on individual figure to enlarge.

If this practice cannot be carried out due to body deformity or illness (such as rheumatism) then some other method of finding North should be used instead.

The equinox posture is to be used around Mar 21st and Sep 23rd equinoxes while Summer and Winter Solstice postures are to be used around your local Summer and Winter solstices respectively.

The index finger in these postures is always aligned with the forearm and is to be kept in line with the line from the elbow to the tip of the index finger.

The angle between the index and the middle fingers should have value of:
90 degrees for Equinox posture
90-23= 67degrees for Winter Solstice posture and
90+23= 113 degrees for Summer Solstice posture. The above angles for Summer Solstice, Equinox and Winter Solstice postures are equal to the angles between a clock hand pointing at 0 minutes and
19 minutes,
15 minutes,
11 minutes respectively. These angles are represented by angles between positions of watch hands on a watch face shown in two following figures.

EcoDriveDuo

Summer Solstice

EcodriveDuo2

Winter Solstice

Figures: Angles between fingers for hand postures at Summer Solstice, Equinox and Winter Solstice are represented by angles between positions of watch hands on this watch face. The long white hand pointing at 0 minute of the watch-face represents the direction of the left index finger of the user of this method while the long red hand represents the direction of his left middle finger (see text).

The long white hand pointing at 0 minute of the watch-face represents the direction of the left index finger of the user of this method while the long red hand represents the direction of his left middle finger.

The angle between the hands on each watch-face has been chosen to match the angle between the line to the Sun on the respective date and the line to the Celestial pole below the horizon. The angle between the red hand and the thick white hand pointing at 15 minutes represent the declination angle of the Sun (or its negative, depending on the observer being in the Southern or Northern terrestrial hemisphere). The variation of that angle through various dates of the year can be found in previous blogs [1,2].

solar-declination-by-a-watch-face

Figure: Determining solar declination using a watch face. (The lines “SOLAR DECLINATION Its rough estimate is required for Fine Alignment of the watch” are to be ignored.)

2. Determine the slope to your Celestial pole.

Sun on Celestial Sphere

Figure: The Sun, the Moon and the stars are attached to a Celestial sphere which encloses the Earth like a giant rotating cage. The cage rotates around the Celestial axis (in cyan-blue color) joining the its two points called the Celestial poles. The horizontal ground of an observer at the center of the celestial sphere is represented by the horizontal great circle of the Celestial sphere while his line of sight to the Celestial pole is represented by the cyan-blue arrow.

The slope from level ground surface to the line of sight to the visible Celestial pole is called the latitude of your place. Practice recognizing it.

Find a level ground. On a clear night set up a stick pointing from the ground to the Celestial pole. In the Northern hemisphere the Celestial pole has a star (Polaris) while in the Southern hemisphere it is only a point on the geometrical figure formed by circum-polar stars. Such a stick is constructed as a shadow rod in any “builder clock”.

Figure: A “builder clock”. The shadow rod of this clock is set to point towards the Celestial pole in the sky.

The inclined shaddow rod on a “Builder Clock” points toward the Celestial pole in the sky when the clock is properly setup with its base in the true North-South direction.

The angle between the stick pointing to the Celestial pole and the ground is called the latitude of the location. The angle between the stick and a vertical plumb line is (90° – latitude). You need to practice recognizing this angle. (Knowing this angle also help you quickly find the Celestial pole from the stars).

Figure: The Northern Celestial pole is the center of this map of the Northern sky.

Figure: The Southern Celestial pole is the center of this map of the Southern sky.

3. Practice reading in degrees the angles between positions of hands on a clock face.

The angle between a hand pointing at 0 minute and another one pointing at
5 minutes is 30 degrees,
10 minutes is 60 degrees,
15 minutes is 90 degrees,
20 minutes is 120 degrees,
25 minutes is 150 degrees,
30 minutes is 180 degrees.

8 Steps for finding true North and time.

1. Determine the current season in the year to select the appropriate hand posture.

The equinox posture is to be used around Mar 21st and Sep 23rd equinoxes while Summer and Winter Solstice postures are to be used around your local Summer and Winter soltices respectively (Each posture can be used for its whole month and a solstice posture can also be used for two adjacent months.).

If the season in the year cannot be determined (as in the case of inhabitants living in artificial environment for years), use the hand posture for equinox days.

2. Determine whether you are in the Northern or Southern hemisphere.

3. Determine if you are in the morning (the Sun is rising before noon) or in the afternoon (the Sun is setting after noon)

This step is needed to select the appropriate hand for the task.

4. Select and use only the appropriate hand for the task:

4a. Northern hemisphere: LEFT hand in the morning THEN RIGHT hand in the afternoon.
4b.Southern hemisphere:RIGHT hand in the morning THEN LEFT hand in the afternoon.

5. Point the index finger to the Sun with your middle finger in its comfortable, nearly horizontal position.

6. Twist the forearm and hand until the middle finger makes with the level ground an angle equal to the latitude angle.

This is illustrated in the two figures.

Find North by Left Hand

Figure: Finding the meridian (true North-South) line with the left hand.

Find North by Right Hand

Figure: Finding the meridian (true North-South) line with the right hand.

7. The projection of the middle finger onto the ground now points exactly away from the terrestrial pole of your hemisphere.

The middle finger now points to the Celestial pole below the horizon, in other terms it points directly away from the visible Celestial pole in the sky.

8. Looking along that direction pointed by the middle finger and imagining a 24-hour clock dial attached to that axis give a natural clock giving time in the day.

Find time by divider

Figure: The line CB to the Sun form the hour hand of a 24 hour clock. This clock face is for Northern hemisphere. In Northern hemisphere the hand sweeps clockwise while in Southern hemisphere it sweeps anticlockwise.

The time given by the natural clock is the local time which has noon when the Sun is highest in the sky. Local time differs from the zonal time selected by the government.

9. Around noon time, either left or right hand can be used. The terrestrial North South line is determined with least accuracy around noon time.

10. On the terrestrial equator, either selection of 4a or 4b can be applied. The middle finger of the selection 4a points at true terrestrial South while that of 4b points at true terrestrial North.

Figure: Summary of the method of finding true North and time from the Sun.

References.

[1]. tonytran2015, Finding directions and time using the Sun and a divider., posted on May 6, 2015.

wpid-dividermwp3e2c2.jpg

find North by the Sun

[2]. https://survivaltricks.wordpress.com/2017/02/13/good-approximation-to-solar-declination-by-a-watch-face/

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Blog image of Contents of Survival sub-page

These are the contents of SURVIVAL sub-page re-organized in book order for coherent reading.

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NAVIGATION (Celestial).

The Sun, the Moon and identifiable stars are used to work out North direction and time in this section.

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. Posted on May 25, 2016

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. Posted on April 05, 2018

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Find North with Orion Equatorial stars

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Slide Sky-Map for displaying tropical stars, posted on October 7, 2016

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Finding direction, distance and navigating to a distant base by stars (Part 1). Posted on January 27, 2016 . This is a novel application for direction of stars in the sky.

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NAVIGATION using only constellations.

The Orion constellation., posted December 26, 2016

The Scorpius constellation, posted on January 8, 2017

The Southern Cross Pointer stars, posted February 26, 2018

NAVIGATION (Terrestrial).

Measuring angles and distances for outdoor survival, posted on June 29, 2016

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NAVIGATION (Instrumental).

Finding North with a lensatic compass, posted on August 21, 2017

Compass-Magnetic

Determining local magnetic declination by a magnetic compass, posted on March 31, 2016

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Shadow stick navigation and graph of solar paths, posted August 19, 2016

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Using GPS in off-grid situations, posted December 06, 2016

Adding longitude and latitude lines to a map, posted August 23, 2017

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Navigating with an AM MW radio receiver, posted January 17, 2017

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Finding North direction and time using geological features, plants and animals, posted August 04, 2017

FIRE MAKING.

Making fire and lighting cigarettes with sunlight. Posted on February 27, 2016

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Pushing away

FOOD

Rice as emergency food., posted December 24, 2016

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Dried-sweet-fruits-as-energy-food, posted December 24, 2017

Air-grown-mung-bean-sprouts-for-food, posted March 07, 2016

MISCELLANEOUS

Old maps:

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Finding North in the polar zones using Equatorial Stars and the Sun.

Finding North in the polar zones using Equatorial Stars and the Sun

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(Blog No.66).

#find North, #finding North, #polar zone, #arctic zone, #Equatorial stars, #Sun, #Viking, #navigation .

Finding North in polar regions using Equatorial Stars and the Sun.

The general principles in Finding North still apply for each familiar method. However Finding North direction in polar regions has its own problems and it is not as simple as for temperate zones due to difficulties caused by steep magnetic lines not pointing to rotational poles, by the closeness of the upper Celestial pole to the zenith, by long extended day time, by aurora light, by aurora interference with radio wave receivers in GPS units.

When those familiar methods encounter problems the method of Finding North by Tropical stars and the Sun can still work and maintain its precision. The Viking may had used this technique in their long sea voyages many centuries ago.

1. The two polar zones

The two polar zones cover any area with absolute value of latitude higher than 66°33′. That is all their points are less than 23°27′ from one of the two poles. The Northern polar (arctic) zone covers parts of Greenland, Iceland, Sweden, Norway, Finland, Russia, U.S. Alaska, Canada with many of their cities. The Southern polar (antarctic) zone covers parts of Antarctica continent (with Argentinian stations, UK Rother station, etc …).
The ratio of the lengths of Day versus Night varies with a yearly cycle on any point of the Earth. In Arctic zone, it reaches 0-100 for some period centered on Winter solstice (on 21 December ) when the Solar path is totally below the horizon. The ratio then varies from 1-99 to 99-1. It then reaches 100-0 for some other period centered on Summer solstice (on 21 June ) when the Solar path is totally above the horizon. The ratio then varies from 99-1 to 1-99 and reaches 0-100 again.
It is similar for Antarctic zone except for the 6 months time difference between the two polar zones.

2. Finding North by GPS.

Find North by a GPS

Figure: A GPS screen.

The easiest way to find North in a polar region is to use the GPS apps on smart phones or on purpose made GPS units.

GPS compass directions are calculated from the change in terrestrial coordinates when you move. The minimum movement distance is only about 5m.

GPS compass directions are true directions and are different from and independent of magnetic compass directions.

However, GPS units may run out of battery, be non-operational during war times, be under heavy interference from polar aurora storms. A non-GPS back up method is still necessary.

3. Finding North by a magnetic compass.

Find North by a compass

Figure: A magnetic compass.

3a. The magnetic poles are not exactly at the North and South poles of the Earth. They are currently in Canada and near to New Zealand respectively. Users of magnetic compasses should know how to compensate for this.

3b. Magnetic lines are also nearly vertically inclined in polar regions making normal compasses sticky with their needles and they may have to be replaced by cruder magnetic rods hung on wire threaded through holes near to their mid-points.

3c. Aurora in the sky changes very slowly and can be used as overhead navigational marks juat like permanent clouds.

4. Finding North using Polaris.

mercator8fx1.6polarc30.jpg

Figure: The Northern and Southern Polar skymaps are represented by two circular discs here.

A real dipper versus Big and Little Dipper constellations

Figure: Photo of a real dipper. Inset: The Big Dipper and Little Dipper constellations.

4a. Polaris in the Little Dipper is right on the North Celestial pole. The North Celestial pole is in the Northern direction of all vertical plumb lines. If the star can be obscured by any plumb line then you eye is exactly on the South of the line. Near to the pole, Polaris is close to the upper extension of any vertical plumb line and it is hard to obscure it by some vertical plumb line.

4b. The altitude of Polaris is most easily read with a Bubble Sextant (Aircraft Sextant) or with a Theodelite (for higher accuracy). The direction with smallest value of altitude of Polaris is Northern direction.
The method is easily applicable at night time but Polaris cannot be seen during day time and during aurora storms.

5. Basis of finding North by Tropical stars.

Find North with Orion Equatorial starsFigure: Panoramic view of the Celestial Equator and the Tropical band from the Arctic zone in December. Stars travel from Front Left to Front Right. The directions and Solar times corresponding to the scale on the bottom of the picture are N(0hr)-E(06hr)-S(12hr)-W(18hr)-N(24hr).

5a. Any point on the Earth sees exactly half of the Celestial Equator above its horizon. The angle between the plane of this half circle and the horizontal one is equal to (90°- latitude).
The Celestial Equator is inclined to the ground and is below the horizon in the North direction in the Northern hemisphere.

5b. Equatorial stars such as the Central Belt Star of the Orion travel along this circle once every day. They rise and set exactly in the exact East and exact West directions respectively.

Find North with Scorpius Equatorial starsFigure: Panoramic view of the Celestial Equator and the Tropical band from the Antarctic zone in June. Stars travel from Front Right to Front Left. The directions and Solar times corresponding to the scale on the bottom of the picture are S(24hr)-W(18hr)-N(12hr)-E(06hr)-S(0hr).



5c. Any tropical star (any star which is no further than 23°27′ from the Celestial Equator) travels along one large (but not great) circle in the sky every day. The circle is “parallel” to the Celestial Equator.

5d. The elevation/altitude of the star varies daily with an amplitude equal to (90°-observer’s latitude) about its daily mean (which is nearly equal to its Declination multiplied by the sine of observer’s latitude)

5e. The North Souih line is the bisector of two directions pointing to any two positions having equal elevations of the same star. The common elevation can be conveniently chosen to be the mean of its 24hr values.

6. Solar trajectory on the Celestial Sphere

The Sun travels along one large (but not great) circle in the sky every day. The circle is “parallel” to the Celestial Equator. The circular Solar path drifts to its most Northern position at 23°27′ latitude on 21 June solstice then drifts to its most Southern position at 23°27′ latitude on 21 December.

At equinox times, the Sun is exactly on the Celestial Equator and rises and sets exactly like an equatorial star.

Locating the hidden Sun by polarized lightFigure: Locating the hidden Sun by polarized light from bright patches of the sky.

Knowing the trajectory of the Sun, you can locate it using polarizing sunglasses even when it is hidden and under the horizon (see ref. [5], Using polarized light to locate the Sun when it is hidden from view).

7. Measuring solar altitude with a stretched hand on an extended arm.

A hand with stretched out fingers hold on its extended arm sustains an angle of about 12 degrees and is a very convenient mean for measuring Solar elevation (altitude) angle in polar regions.

8. Variation of Solar altitude/elevation during the day.

Solar elevation/altitude varies daily with an amplitude equal to (90-latitude) about its daily mean (which is nearly equal to Solar Declination of the day multiplied by sine of local latitude).

You can tell where is the Sun on its daily cycle by measuring its altitude with a stretched hand on an extended arm.

As the Sun travels on a known wavy line its altitude gives both its compass direction and the corresponding time of the day.

The directions and times corresponding to the scale on the bottom of the first panoramic picture (for Arctic regions) are N(0hr)-E(06hr)-S(12hr)-W(18hr)-N(24hr).

For Antarctic regions the directions and times corresponding to the scale on the bottom of the second panoramic picture are S(24hr)-W(18hr)-N(12hr)-E(06hr)-S(0hr).

9. Time estimation from Solar altitude

Solar altitude may give a better time estimation near to Sunrise and Sunset.

The time is 6hr or 18hr when the altitude of the Sun crosses its mean value.

10. Distinguishing AM from PM

When using the Sun for navigation, it is important to know whether the Sun is ascending (AM) or descending (PM).

10a.A 24hr sub-dial on a clock face is certainly useful in telling AM and PM.

10b. Ambient air temperature after receiving daylight radiation is also usually higher in PM time than in AM time.

10c. There are different sets of stars in the sky for AM and PM in the night.

10d. Birds activities are different in AM and PM.

10e. Your biological clock (circadian rhythm) may help distinguishing AM and PM.

11. Finding North with a watch in a polar region

Finding North with a watch

Figures: Finding North with a watch for antarctic and arctic zones.

Finding North with a watch needs a modification: If you can travel to the nearest pole in 2hr, you have to remember that the 6-12 line on the watch points along the meridian line of your home city, not toward the Pole of the Earth. Indeed, you can travel around the pole but that 6-12 line keeps its direction along the meridian of your home city.

The watch face can be simply laid horizontally as in the original “Scout method” without generating any noticeable directional error.

Figure: A map of the arctic from National Oceanic and Atmospheric Administration (https://www.pmel.noaa.gov/rediscover/resources). All meridional lines converge at the pole.

12. Finding North with a divider in a polar region

solar declination from a watch face

Figure: Estimating Solar declination by drawing a watch face with a subdial.

Finding North by a divider

Figure: Finding North by a divider.

The divider method is still applicable for finding direction and time but requires high accuracy in Solar declination and latitude angle for setting the divider.

A small plumb line hanging from the stem of the divider can improve the accuracy for its latitude angle setting.

With the above additional plumb line, the divider can measure the altitude of the Sun to give a good estimate of time.

13. Finding North with an AM Broadcast radio receiver in a polar region

AM radio usable for Finding North direction

Figure: An AM Broadcasting radio receiver wirh an internal ferrite rod antenna.

The method of finding direction using an AM radio receiver tuned to nearby broadcasting ([8]) is useful near to cities with AM broadcasts in polar regions. The transmission is not effected by low visibility from bad weather. You need a map of the region with AM transmitters as landmarks.

References.

[1]. tonytran2015, Using GPS in off-grid situations., https://survivaltricks.wordpress.com/2016/12/06/using-gps-in-off-grid-situations/, posted December 6, 2016

[2]. tonytran2015, Selecting and using magnetic compasses, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2016/07/09/selecting-and-using-magnetic-compasses/, posted 09/7/2016.

[3]. tonytran2015, Finding North direction and time by stars, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/08/28/finding-north-and-time-by-stars/ , posted on August 28, 2015.

[4]. tonytran2015, Finding North and time by stars in the tropics, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2016/05/25/finding-north-and-time-by-stars-in-the-tropics/, posted on May 25, 2016

[5]. tonytran2015, Using polarized light to locate the Sun when it is hidden from view, https://survivaltricks.wordpress.com/2015/05/09/using-polarized-light-to-locate-the-sun-hidden-behind-clouds/, posted on May 9, 2015

[6]. tonytran2015, Finding accurate directions using a watch, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/05/19/finding-accurate-directions-using-a-watch/, posted May 19, 2015

[7]. tonytran2015, Finding directions and time using the Sun and a divider, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/05/06/finding-directions-and-time-using-the-sun-and-a-dividing-compass/, posted on May 6, 2015.

[8]. Navigating with an AM MW radio receiver.

[9]. https://www.pmel.noaa.gov/rediscover/resources.

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Quick fire making using sunlight.

Quick fire making using sunlight.

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(Blog No.44).
#make fire, #making fire, #fire, #Sun, #sunlight, #crystal, #glass #ball, #sphere, #lens, #ocular, #monocular #sun-rays, #survival.

You may already have in your possession some excellent lenses for making fires. Knowing about them will help you make fire quickly from sunlight when facing an emergency. All lenses described in this blog can make a cigarette smoulder in less than 30 seconds and can light up that cigarette afterwards.

1. Concentration of radiating heat flux by a lens.

The radiating heat flux from the Sun is concentrated by a factor C given by

C = Pi*d*d/(Pi*f*a*f*a) =

C = (d/f)*(d/f)*(1/a)*(1/a).

where d and f are respectively the diameter and focal length of the lenses and a is the angular diameter of the Sun (a = 0.5*3.14/180radian = 0.0087 radian).

The angular diameter of the Sun cannot be changed. It is obvious that we have to increase the ratio (d/f), which is called the aperture number of the lenses, to increase the heat flux concentration. The deciding factor for success is the aperture ratio of the mirror or lens system.

C = 13200*(d/f)*(d/f).

This concentration of heat flux is remarkably high for any lens system with D/f of more than 1/3 and can be used to ignite properly prepared tinder to make fire in survival situations.

The calculated concentration of radiating heat flux can only be achieved using precision optics. Any imperfection on the surface of the lens disperses the image of the Sun and reduces the concentration drastically.

2. A transparent perfect sphere.

crystalballc70.jpg

Figure 1 : A small clear sphere (25mm diameter).

crystalball2c70.jpg

Figure 2 : Small clear sphere (close up view).

You may have a small clear glass sphere somewhere in your household either as a decorative item, or as a bottle stopper, etc…

The small transparent sphere I use here is a small (25.4 mm diameter) clear quartz sphere often used as an item of curiosity and often called a “crystal sphere” by fortune tellers.

Calculations using geometrical optics show that (for n=1.5) the focal point is about 0.5 radius outside the surface of the ball and the equivalent focal length of the sphere is about 2r×(3/4)= 1.5r

Even if only rays of distance less than 0.5 radius (from the central ray) converge on the spot, the aperture of the sphere is still
D/f = (2*0.5r)/(1.5r) = 1/(1.5),

a high value for aperture.

At an aperture value of 2/3, the concentration of radiating heat by sunlight is

C = 13200*(D/f)*(D/f) = 6000.

The actual aperture number of this clear sphere is higher than 1/1.5 and the sphere can be used as a lens to light up cigarettes using sunlight.

Figures 3 : Lighting a cigarette by a small 25mm clear quartz sphere.

The above photo also demonstrates the danger of leaving clear glass balls on any combustible surface. When the afternoon Sun comes down to an elevation of 41degree (= arcsin 0.6666), the image of the Sun is exactly on the combustible material and combustion becomes a real possibility !

The concentration factor of C = 6000 is only realized with a perfect sphere. For any body of revolution of nearly spherical shape, the concentration of radiating heat flux is much lower, and may come down to C = 100 when there is some appreciable astigmatism. For this reason, PRECISION IS MORE IMPORTANT THAN SIZE for transparent spheres.

I prefer having a small perfect sphere to a large approximate sphere.

3. A watchmaker double staged ocular.

Figure 1: A watch maker monocular.

Figure 2 : A watch maker monocular (rear view).

Figures 3 : Lighting a cigarette by a watch maker monocular.

A monocular is a compound magnifying lens used by watchmakers to see small details of watch movements. It is a simple version of the oculars used for each eye in common sport binoculars.

Every first aid kit for hikers should have this light weight and useful device and a pair of sharp tweezers for detecting and removal of hurting spikes or splinters sticking in the skins.

The lens nearer to the eye of a proper ocular has a large diameter to give the eye a wide field of view. The double stage makes tiny object has a large image at infinity.

When sunlight travels in the reverse direction from the back (big) end to the front (small) end it will focus at a tiny spot outside the ocular and about 20mm from the front lens.

The aperture ratio D/f of this compound lens is about 1/2.

If the dark end of a cigarette is placed at that bright tiny spot smouldering will begin in less than 1 second on a sunny day.

If the oculars of your binoculars are thread removable then you can also use them in emergency but keeping in mind that taking apart a pair of binoculars will allow dirt to contaminate it.

The concentration factor of C = 13200*(d/f)*(d/f) is only realized with a lens having perfect spherical surfaces. For any lens with only approximate shape, the concentration of radiating heat flux is much lower, and may come down to C = 100 when there is some appreciable astigmatism. For this reason, PRECISION IS MORE IMPORTANT THAN SIZE for any monocular.

I prefer to have a small quality monocular than a large one with low quality.

4. Aspherical condenser lenses.

Figure 1: A fused quartz aspherical lens.

Figure 2: Fused quartz aspherical lens viewed from another direction.

I was lucky to be given a fused quartz, thick aspheric lens. Its aperture ratio is about D/f=1/1.5 while other thin spherical, glass lenses have a ratio of less than 1/2.5.
The concentration of solar heat flux is much higher when using it than when using an ordinary magnifying glass.

Figure 3: A one battery LED torch with a thick aspherical lens at the front.

The front lenses of zoom focus LED torches are low cost substitutes for such aspherical lens. They do work exceptionally well and are even unbreakable since they are made from (acrylic ?) plastic.

Disadvantage.

The disadvantage of using any such aspherical lens for making fire is that it is heavy and it has very short distance from its flat side to the bright focal point. Sunlight coming to this bright focal point from many widely separated directions and it is difficult to direct them all to the trough of the dimple at the center of the end of a cigarette. I found that it is less easy to light up a cigarette using an aspherical lens than using a good monocular of the same diameter.

Again, it is important to also note that PRECISION IS MORE IMPORTANT THAN SIZE for any aspherical lens.

I prefer to have a small quality aspherical lens than a large one with low quality.

5. A flexible Fresnel lens for wallet.

Figure 1: A thin flexible Fresnel lens for wallet. Concentric grooves can be noticed at the right hand corners of this picture.

The lens is usually made of thin, flexible, soft clear plastic of the size of credit cards. This type of lenses is sold as wallet sized magnifying glasses for map reading.

A Fresnel lens has high aperture ratio and can be used to light up cigarettes with ease. However it needs to be properly cleaned after each use as it is easily scratched.

6. Method of lighting up a cigarette using a small lens.

1. A cigarette or its imitation made up from rolled up toilette tissue sheets with darkened ends seems to be the readily available suitable tinder sticks for making fire using sunlight.

2. A conical dimple should be made at the dark end of a cigarette. The depth of the dimple should be about the size of its radius. That is a conical concave surface should be made out of the dark flat tip of the cigarette. This tiny concave surface reduces radiating heat loss from the fire to be started at its trough.

3. A precision lens is used to focus sunlight onto the dark end of a cigarette. PRECISION IS MORE IMPORTANT THAN SIZE as the high concentration of sunlight depends on precision of the lens surface.

4. The axis of the lens system should point exactly at the Sun to have maximum amount of sunlight converging on the focal point.

5. Sunlight should be focused on one point on the surface of the dimpled end of the cigarette to blacken it. Smoke should be seen arising from the spot within 10 seconds after focusing. Other points of the surface should then be smothered to have all the surface gradually blackened.

6. Sunlight is now focused on the trough point of the dimpled surface. Smoke will be seen and the trough will glow red when assisted by gentle wind blowing toward the other end of the cigarette.

7. The cigarette should now be smoked or blown externally so that hot fume from the flame end travels toward its other end to heat up the adjacent zone to ready it for combustion.

8. A strong red glow indicates that the cigarette has been burning. It can now be used to start up a fire.

References

[1]. tonytran2015, Making fire and lighting cigarettes with sunlight, survivaltricks.wordpress.com, Making fire and lighting cigarettes with sunlight, posted on February 27, 2016

[2]. tonytran2015, Mirror for making fire using sunlight, survivaltricks.wordpress.com, Mirror for making fire using sunlight, posted on April 13, 2016

Appendix: Calculations for the spherical lens.

The focus point is about 0.5 radius outside the surface of the ball. D/f is about 0.7.
Front face

1/f = (n-1)(1/r1 + 1/r2)
f = r/(n-1)

f = 2r front

Let d be the distance from the front surface to the focal point.

d = r/(n-1) in air, rn/(n-1) in glass

d=2r in air, 3r in glass
Let d1 be the distance from the Rear surface to the focal point to.
d1 = rn/(n-1)-2r = r(-n+2)/(n-1) in glass,

r(-n+2)/(n×(n-1)) in air

d1 = r in glass, 2r/3 in air

1/d2 = 1/(2r) + (n×(n-1))/( r(-n+2) )

=(1/((2r)× (2-n)))×(2-n+2n×(n-1))

1/d2= (1/((2r)× (2-n)))× (2n*n-3n+2) for n=1.5,

1/d2 = 1/(2r) + 3/(2r)
d2 = 0.5r

Rear magnification:

0.5/(2/3) = 3/4

Equivalent focal length of the sphere is

2r×(3/4)= 1.5r
Calculations using geometrical optics show that for n=1.5 the focal point is about 0.5 radius outside the surface of the ball and the equivalent focal length of the sphere is about

2r×(3/4)= 1.5r

Aperture is

D/f=4/3.

Obviously actual parallel rays at one radius distance from the axis of the ball cannot converge on the bright spot.
Note that the radiative heat flux from the Sun is concentrated by a factor C given by
C = Pi*d*d/(Pi*f*a*f*a) =
C = (d/f)*(d/f)*(1/a)*(1/a).
where d and f are respectively the diameter and focal length of the lenses and a is the angular diameter of the Sun (a = 0.5*3.14/180radian = 0.0087 radian).
The angular diameter of the Sun cannot be changed. It is obvious that we have to increase the ratio (d/f), which is called the aperture number of the lenses, to increase the heat flux concentration. The deciding factor for sucess is the aperture ratio of the mirror or lens system.
Even if only rays of distance less than 0.5 radius converge on the spot, the aperture of the sphere is still

D/f = (2*0.5r)/(1.5r)

= 2/3 = 1/(1.5),

a high value for aperture.

At D/f of 2/3, the concentration of solar heat is

C = 13200*(D/f)*(D/f) = 6000.

PREVIOUS SURVIVAL blogs

Making fire and lighting cigarettes with sunlight. Posted on February 27, 2016

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Mirror for making fire using sunlight., posted on April 13, 2016

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Rice as emergency food., posted December 24, 2016

20161230_192839ricegrains2c60.jpgThe Orion constellation., posted December 26, 2016

Rice as emergency food.

Using GPS in off-grid situations.

Slide Sky-Disks with grid masks showing azimuths and altitudes.

Slide Sky-Map for displaying tropical stars..,,..all.

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Finding North direction and time by any bright star.

NorthByKnownStar

Finding North direction and time by any bright star

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#find North, #find, #direction, #time, #bright star, #Sun, #divider, #navigation.

Find North Direction and time by any bright star.

Most people living in the Northern temperate and arctic zones know how to find the star Polaris to find North direction and can even tell time by the orientation of the Little Dipper (part of the Little Bear). But Polaris is not an easily seen bright star and may even be hidden from view for people in Tropical zone and in Southern Hemisphere.

This posting shows how to use ANY arbitrarily known star to find North direction and time, and is useful to non-users of Polaris star. The method is similar to that given previously using the Sun [1] and is useful when only one bright star is visible in an unclear sky (affected by thick clouds or pollution).

The divider compass in this posting is only for instructional purpose and is not needed in actual application. The user may use any two of his fingers instead.

1. Requirements by the method.

To apply this method you need:
1. Your current latitude,

2. The current date in the Solar Year,

3. An unmistable bright star,

4. Its Declination and its Right Ascention already converted to Date of that Star in the Solar Year (see the details on the Conversion in the following section).

2. The date of a star.

BrightStars20Plus2

Figure: Table of bright stars with their approximate dates .

The date of a star should be known, even only approximately by the month, if the user wants to tell time from that star.

The date is obtained from the linear conversion:

a. 00:00 hr of R.A. —-> Sep 23 in Date

b. 06:00 hr of R.A. —-> Dec 21 in Date

c. 12:00 hr of R.A. —-> Mar 21 in Date

d. 18:00 hr of R.A. —-> Jun 21 in Date
Any star is visible nightly (either from Sunset to its setting or from its rising to Sunrise) for more than 9 months each year. The visibility cycle for each star begins with the star seen rising near the Eastern horizon few minutes before Sunrise. On subsequent days, the star rises earlier and earlier, it travels gradually towards the West and remains for longer and longer duration in the night sky until one day it stays for the whole night. The star is therefore called a star of that date. After that day, the star is seen setting in the West in the night. On subsequent days, its lead on the Sun gradually increases and it sets on the West at earlier and earlier time. Near the end of the cycle, the star is visible above the Western horizon for only few minutes after Sunset. It then sets on the West. At the end of this cycle, the star is too close to the Sun to be visible in the sky. The cycle then repeats from the beginning.

Example:

Boote Arcturus is a star of April 25th with declination 19 degree N. Step 6 of reference [2] shows how to easily identify it.

It reaches its highest elevation at mid-night of that date and remain visible for that whole night.

In February it rises about 4 hr after Sunset and has not enough time to complete the journey to the West. On April 25th it rises at about Sunset to complete the journey to the West about Sunrise. In June it is seen already high in the sky at Sunset and set on the West 4 hr before Sunrise.

3. Selecting a star for current month in the year.

PolrNorthNC20const8

Figure: Sky map (Inversion type) of the Northern Celestial 3/4-sphere showing only 20 brightest stars and some constellations.

polrsouthq3c60.jpg

Figure: Sky map (Inversion type) of the Northern Celestial 3/4-sphere showing only 20 brightest stars and some constellations.

Select a bright star of a date in the year near to your current date (or month) and read its declination from any source such as the internet, your own tables or the two star maps supplied here. If you use the star maps, its declination is read from the constant declination circles and its date from the rim on the opposite side (that is also the point closest to the Sun on the elliptic circle).

This method requires POSITIVE IDENTIFICATION of your chosen star. To positively identify it, you may need to see

1/- either neighbouring bright stars, their relative distances and orientation

2/- or surrounding dimmer stars making up the constellation containing it.

When that star is the only visible one in the sky you may have to identify it relying on its appearance details in previous nights such as:

1/- Continuity of its characteristics from previous nights (or hours),

2/- its elevation after Sunset,

3/- its relative directions from the setting Sun or the (moving) Moon,

4/- its ranking as the few brightest objects in the sky after Sunset.

Stars near to the elliptic may sometimes be confused with much brighter planets and their use involves extra cares.

If you are away from the two polar zones and always can see an unobstructed sky (nearly half of the Celestial sphere), you only need to find one of the 3 stars Orion Rigel, Boote Arcturus and Altair to apply this method.

4. Rules for turning to lower Celestial pole.

divider43.jpg

Figure: The rule for finding North by any chosen star is similar to the rule illustrated here for the Sun.

Be certain of your hemisphere and whether the star is rising (early star) or setting (late star) to turn the second leg of the divider to the left or to the right. This is similar to the requirement for finding North using the Sun.

Then apply all the steps of the next section.

5. Steps to find North direction and time using a star.

DirectionTimeByStars

Figures: Summary of steps to find North direction and time by any known star.

When any star is used on its date in the year, the Sun leads it by exactly 12 hours. For every month after that, the lead by the Sun is reduced by 2 hours (or every 12 months by 24 hours). The last figure of the illustration shows the Sun leading the star by about 5 hours on the Celestial clock face.

Example 1:

In December, January, February use Sirius if you can see it.

Sirius is a star of Jan 1st with declination 17 degree S. Step 8 of reference [2] shows how to find it.

On Jan 1st the time determined by Sirius is 12 hours behind the time by the Sun.

On April 1st, the time determined by Sirius is 6 (=12-3*2) hours behind the time by the Sun.

Example 2:

In March, April, May use Boote Arcturus if you can see it.

Boote Arcturus is a star of April 25th with declination 19 degree N. Step 6 of reference [2] shows how to identify it.

On April 25th the time determined by Boote Arcturus is 12 hours behind the time by the Sun.

On May 25th, the time determined by Boote Arcturus is 10 (=12-1*2) hours behind the time by the Sun.

On June 25th, the time determined by Boote Arcturus is 8 (=12-2*2) hours behind the time by the Sun.

References.

[1]. tonytran2015, Finding directions and time using the Sun and a divider., survivaltricks.wordpress.com, posted on May 6, 2015.

[2]. tonytran2015, Finding North and time by stars, survivaltricks.wordpress.com, posted on August 28, 2015.

RELEVANT SURVIVAL blogs (Added after February, 2017)

Caution in finding North by bisector line of a horizontal watch. Posted on October 28, 2015
, posted on 2018 July 10

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Finding directions and time using the Sun and a divider., posted on May 6, 2015. <<<—This is my MOST USEFUL novel technique.

wpid-dividermwp3e2c2.jpg

find North by the Sun

Finding North direction and time using the hidden Sun via the Moon . Posted on July 6, 2015

image

Finding North direction and time accurately from the horn line of the Moon. Posted on August 12, 2015. This is my novel technique.

image

Finding North direction and time using the Moon surface features. Posted on July 1, 2015.

image

, posted on

Finding North and time by stars. Posted on August 28, 2015 .

Sky map Northern 3/4 sphere

Sky map Southern 3/4 sphere

Finding North and time with unclear sky. Posted on October 17, 2015.

image

image

 

Navigating with an AM MW radio receiver, posted January 17, 2017, The Scorpius constellation, posted January 8, 2017, The Orion constellation., posted December 26, 2016, Rice as emergency food., Using GPS in off-grid situations, Slide Sky-Disks with grid masks showing azimuths and altitudes, Slide Sky-Map for displaying tropical stars.

Click here for my other blogs on divider43.jpgSURVIVAL

Click here for my other blogs on divider43.jpgSURVIVAL

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Making fire and lighting cigarettes with sunlight

Making fire and lighting cigarettes with sunlight

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#make fire, #making fire, #fire, #Sun, #sunlight, #sunray, #lens, #magnifying glass, #mirror, #survival.

StormWatchDiagram

Figure 1: Diagram of making fire by a mirror.

StormWatchBurnsCig

Figure 2: Lighting a cigarette by sunlight. Smouldering is visible after 27seconds.

I used here

1. a device consisting of a lens and a mirror right behind it (see following pictures),

2. then another alternative device being the dial face of an unusual Storm brand Remi watch (in the above pictures).

The combination of a lens and a mirror right behind it produces a large aperture system giving high power concentration and it also has light weight and convenience for cigarette lighting. My 60mm lens and mirror system with aperture ratio of d/f =60/65 = 1/1.1 regularly makes cigarette fire in 15seconds.

The Storm brand watches has an interesting unusual Remi model that has a mirror face with 2 small and 6 tiny windows for displaying painted numerical hours, minutes and fraction of a minute. The rest of the face acts like a concave mirror of 38mm diameter. The pictures show one such watch I could get hold of. The equivalent mirror has a focal length of 75mm (aperture ratio of d/f = 1/2.5) and I had been able to use it to light up a normal (dry, not wet) cigarette in less than 60seconds!

Having a lit cigarette is having a fire on hand.

The advantage is that a normal cigarette can be lighted on any sunny day in 5 minutes with minimal set up.

The disadvantage is that smoking is harmful to your health. You have to light up a cigarette but smoking it is not encouraged !

The steps are described in details as in the following.

1. Selecting a magnifier with large aperture.

MagnifierMirror

Figure 1: A mirror attached to a 60mm clear, colourless glass lens. This system with aperture ratio of d/f=1/1.1 can light up a cigarette in only 15 seconds. This is my favourite set up.

SphericalSpoonForBurning

Figure 2: Even a polished spherical soup spoon with high aperture ratio can also light a cigarette.

It is shown here the success of this method depends on having a high aperture ratio.

The concentration of sun-ray heat is proportional to the square of the aperture of the lens and mirror system. Concentrated heat burns fuel easily. Select a lens and mirror system with a large aperture (high ratio of diameter to focal length) for fire making by sunlight.

A reflective mirror right behind a convex lens nearly doubles the aperture ratio of that single lens and increases concentration of power by nearly four times around the new focal point (on the Sun’s side).

Transmission media absorb energy. Select magnifying glass made from clear, colourless material. I found that clear, colourless glass is best for this purpose.

Only 40% solar radiation energy is in visible sunlight, the other 10% and 50% are in Ultra Violet and Infrared respectively. Some materials may not allow these part to pass through in the same way as visible light. The choice of materials is thus important in making collimated solar power.

Aperture ranking of various systems:

The aperture ratios of familiar systems are

d/f = 1/1.1 for the system in the pictures (lens plus mirror),

d/f = 1/1.5 for the aspherical, plastic front lenses of most focusing LED torches,

d/f = 1/2.5 for the Storm watch,

d/f = 1/2.5 for common magnifying glasses with medium thickness,

d/f = 1/4 for common magnifying glasses with thin thickness.

The spoon head in use here is almost a concave spherical mirror with quite high ratio of d/f=1/0.4 . However it does not light up the cigarettes very quickly as expected because it is not an ACCURATE mirror and the picture of the Sun at its focal surface is not clearly defined and too spread out.

It takes 12sec, 15sec and 40seconds to light up a cigarette using that spherical spoon (when WELL POLISHED), the lens with attached mirror (in the picture) and the Storm watch respectively. When the spoon was dull and unpolished, it took up to 120 seconds to light the cigarette.

A common, colourless, thin magnifying glass with d/f = 1/4 can still make a well prepared cigarette/tinder stick smoulder (in less than 5 seconds) using sunlight from even a late afternoon Sun at low (20 degrees) elevation.

Even a small, 16mm diameter, plastic front lens with d/f=1/1.5 of a focusing LED torch (powered by a single AA-battery, pictured at the end of the article) has been successfully used to consistently ignite (in less than 5 seconds) my well prepared charred stick of rolled up (10cmX10cm) sheet of toilette tissue by focusing afternoon sunlight (from the Sun at 30 degrees elevation, in a clear sky) onto it.

2. Alignment

StormWatchDiagram

Figure 1: Aligning the Storm watch and the cigarette for making fire.

StormWatchFront

Figure 2: Front view of the unusual Remi model of watches by Storm.

Align the axis of the watch toward the Sun.

From the 3 o’clock direction of the watch (in front of the dial windows which do not reflect much sunlight), hold a normal (dry, not wet) cigarette to have its tip reaching the focal point.

It may help to have the mirror axis pointing slightly from the Sun so that the cigarette and the hand holding it cast no shadow on the mirror.

The cigarette should be nearly parallel to the watch dial. The butt of the cigarette should be slightly away from the dial and the tip should be near the focal point and be brightly shone by collimated sunlight reflected by the mirror dial.

If a concave mirror or a lens is used instead of the above watch, align its axis towards the Sun to minimize the picture at its focal plane.

3. Focussing

The distance from the tip of the cigarette to the center of the dial should be varied until the reflected sun-rays is collimated into the smallest spot on the dark tobacco cuttings (fibers) at the central axis of the cigarette. Do not focus sun-rays on the enveloping white paper as white objects bounce back more radiative heat than dark objects.

WARNING: Prolonged looking at the concentrated (focused) sun light reflected off white enveloping paper of the cigarette may injure your eyes.

4. Smouldering needs time.

StormWatchFocussng

Figure 1 : Lighting a cigarette by the Storm Watch at 27sec.

SphericalSpoon

Figure 2 : Lighting a cigarette by a spoon 12seconds.

Figure 2 shows smouldering using the polished, spherical head of a stainless steel soup spoon.

Keep the center of the cigarette tip so heated (by collimated, reflected sun rays) for about 3 minutes until there is sign of smouldering with steady smoke rising from it.

Smouldering takes 5sec and 12sec respectively for system of the lens plus mirror and for the WELL POLISHED spherical spoon. The spoon does not have an accurate spherical shape and its reflected sunlight is not well focussed.

5. Turning smouldering into fire by gentle wind

For smokers: Suck air in through the butt of the cigarette to intensify the smouldering into a red glow of cigarette fire.

For non-smokers: Directing your gentle air blow from the tip to the butt of the cigarette may also have the same effect.

Due to the required flow of hot fume through the inside of the cigarette, it is best to start the smouldering with sun rays on the dark material at the tip of the cigarette to start smouldering then slowly tilt the cigarette at angle, keeping the smouldering, to have sun rays heating the hot spot through the side while hot fume can go up inside the cigarette and exit at the other end.

This method of lighting a normal cigarette by sun rays using the watch face has been actually tested successfully on a dry (Summer) day at 15hr, on November 11th, 2015 in Melbourne (39 degree South in latitude), Australia. It has been successfully repeated on many subsequent sunny, dry days.

A roll of tinder made of dried fibers or charred cotton may be used instead of a cigarette. However cigarettes seem to be the best rolls of tinder readily available for this method of making fire.

A rolled up sheet of well crumbled newspaper material (non-gloss material with loosely adhering fibers) in the shape of a long cigarette may partially provide the flammability of a cigarette and may also be used here instead of the cigarette. You may expect longer time to smouldering in this case.

Note:

A smouldering rarely turns into a cigarette fire without AIR FLOWING FROM THE TIP TO THE BUTT INSIDE the cigarette.

6. Making a stick of tinder for making fire by sunlight.

TinderToiletTissue.jpg

Figure 1: A rolled up sheet of toilette tissue to be made into a tinder stick. Inset: The remaining last third of such a stick after ignition started by concentrated sunlight from a magnifying glass.

TinderCharredTissue.jpg

Figure 2: A stick of rolled up toilette tissue with charred end.

A stick of tinder can be made by rolling up moderately tightly a 20cm long sheet of toilette tissue into the shape of a long cigarette. A DARK MARKING of more than 2mm diameter should be made with a pen or a ball pen on the outside surface of such a stick to let it absorb sunlight heat to start the smouldering. Such a stick burns almost like a cigarette when externally blown with steady, gentle, fresh wind.

Loose rolling allows the fume to flow inside the stick from the fire end to the other end to heat up and deposit flammables on the next section of tinder, readying it for the fire but may make the fire propagate unevenly across the cross section of the stick. Tight rolling gives the fire time to spread evenly across the cross section but may restrict the flow of the fume to heat up and deposit flammables on the next section of tinder. An optimal balance can be found between the two extremes by fine tuning the tightness in rolling.

A tightly rolled up sheet of crumbled newspaper material (non-gloss material with loosely woven fibers) in the shape of a long cigarette may also make an alternative (but admittedly poorer) substitute for a cigarette. A DARK MARKING of more than 2mm diameter should be made with a pen or a ball pen on the outside surface of such a stick to let it absorb sunlight heat to start the smouldering. You may expect longer time to smouldering with this roll.

A roll of broken dried leaves inside a rolled up dried leaf can also be used as a (poorer) substitute for a cigarette. The enveloping leaf may get slightly broken when rolled up. The broken dried leaves inside the roll should be tightly packed (and even refilled and compacted again and again after rolling the enveloping leaf) to be able to maintain the smouldering. A DARK SPOT of more than 2mm diameter should be created on the side surface of the roll to let it absorb sunlight heat from the side for smouldering so that fume can flow upwards inside the roll. You may expect longer time to smouldering with this roll and you may have to exert a lot of wind blowing onto the tip of the roll to intensify the smouldering into a red glow.

Commercial cigarettes seem to have been optimized for such burning and appear to be best (although costly) for use as tinder sticks. A stick of rolled up toilette tissue ignites and burns as well as a fresh cigarette. A stick of rolled up crumbled newspaper is a close replacement. However, a stick of fake cigarette or fake cigar made from broken dried leaves inside a paper roll ignites very poorly due to loose packing.

Without the dark spot, the time to smouldering for a rolled up sheet of toilette tissue is more than 20 times the corresponding time with the dark spot. I suppose that the white tissue reflect more than 97% of sunlight heat while the dark spot allows it to absorb about 50% of sunlight heat.

Making a charred stick of tinder out of a rolled up sheet of toilette tissue.

A charred tinder is made up of almost pure carbon. It has higher ignition temperature, but it does not conduct heat and it is black, absorbing sun ray heat most efficiently. Since it absorbs sunlight heat and has poor heat conduction, its temperature can rise quickly past its spontaneous combustion temperature when shone by concentrated sunlight. It is thus most suitable material for starting fire with sunlight, burning even with a moderately concentrated beam.

A well prepared charred stick of rolled up sheet of toilette tissue can even be ignited by using only a small, plastic, 16mm diameter front lens of a LED torch to focus afternoon sunlight (from the Sun at 30 degrees elevation, in a clear sky) onto it.

Any combustion of organic materials is a combination of many competing chemical reactions. By reducing the concentration of oxygen in the surrounding gas, the burning of carbon can be drastically reduced while the decomposition of organic compounds into carbon, hydrogen, oxygen and nitrogen can still proceed, producing a skeletal frame, made entirely from carbon, of the material. This gives a charred object in the shape of the original object.

A charred stick of tinder can be made as in the following:

Make a red glow at one end of the stick (with a magnifying glass or with another source of fire). Hold the glowing end of the stick downward, stick it into the center of a fully blown up, clear bag of poly-ethylene (of 500mL of 1000mL capacity), away from the wall of the bag, and twist the open end of the bag around the stick to keep the bag pressurized and the red glow away from its wall, then keep twisting past the stick. The result is a closed blown up bag with a tinder stick burning inside it, away from the wall. After about 1 minute, the inside of the bag is starved of oxygen and the red glow reduces to a low temperature fire charring it adjacent material. Wait for 10 minutes for any fire to extinguish then take the stick out of the bag. One such stick with a charred end is illustrated in the figure.

7. Some unusual but fast ways to light up a cigarette for making fire.

FireFromSpoon

Figure 1: Lighting a cigarette by a WELL POLISHED spherical spoon head with d=50mm, f/d=1/0.4 at 12s, 9s, 7s, 4s, 0s.

FireFrKeyRingMagnifier

Figure 2: Lighting by a small glass lens with d=21mm, f/d=1/2.5 at 16s.

8. Making fire with a serving spoon and a cigarette.

FireFrNewSoupSpoon

Figure: Reverse sequence of burning a cigarette by a 60mm, POLISHED, SPHERICAL serving spoon at 37s second. This spoon has a very high aperture ratio, D/f = 3.5.

An insulated copper wire has been wound on the handle of the 60mm, POLISHED, SPHERICAL serving spoon to hold the cigarette. The focal point is on the plane defined by the rim. No blowing is necessary with this large system. The smouldering turns into a cigarette fire by itself.

This was carried out in Vietnam (Saigon) on December 14 (mid-winter) under a clear sky; air temperature was 30degree C, the air was dry and the elevation of the Sun was 55degrees. The cigarette brand was Craven, readily available locally, with light brown leaves.

The cigarette can also be replaced by a stick of rolled up 20cm sheet of toilette tissue (with a DARK MARK made on the end or the edge of the end to absorb heat of collimated sunlight).

Selecting a spoon for collimating sunlight.

The easiest choice is with spoons having spherical spoon heads. The chosen spoon head should be well polished and should have shiny reflections. The focal point of any spherical surface is one half (1/2) of the curvature radius from the surface.

From a distant point on the spoon head’s axis, a very small spot on the cigarette tip placed at the focal point should be seen magnified to be bigger than the whole spoon head. All sunlight reaching the spoon head will travel backwards along those paths into that small point at the tip of the cigarette to heat it to high temperature.

For any common elongated spoon head, put the tip of a pencil at the estimated focal point and look at the spoon head from various directions. If any small part of the of the tip can be seen to be magnified to occupy more than 40% of the surface of the spoon head from some direction, it is possible to use such spoon head to heat up a small part of the tip using the sunlight coming from the viewing direction. The spoon must pass this test before you can try to ignite anything using its collimated sunlight. (Most common elongated spoon heads do NOT pass this test.) For common elongated spoon heads which have passed the test, the Sun usually has to be offset 60 degrees from the normal axes of the spoon heads for making fire. Only elongate spoon heads which can easily light up traditional match heads using sunlight should be experimented in lighting cigarettes/tinder sticks.

9. Notes on making fire by a magnifying glass.

MagnifierLEDTorch

Figure: Making fire, even with a small, 16mm in diameter, plastic front lens of the focusing LED torch (powered by one single AA battery) in this picture can be consistently carried out by igniting (to make fire) in less than five seconds a well prepared charred stick of a rolled up (10cmX10cm) sheet of toilet tissue (ambient temperature was 34 degrees C, humidity 30%, elevation of the Sun was 30 degrees in the tests).

Users of this method should remember that:

1. The radiative heat flux from the Sun is concentrated by a factor C given by

C = Pi*d*d/(Pi*f*a*f*a) =

C = (d/f)*(d/f)*(1/a)*(1/a).

where d and f are respectively the diameter and focal length of the lenses and a is the angular diameter of the Sun (a = 0.5*3.14/180radian = 0.0087 radian).

The angular diameter of the Sun cannot be changed. It is obvious that we have to increase the ratio (d/f), which is called the aperture number of the lenses, to increase the heat flux concentration. The deciding factor for sucess is the aperture ratio of the mirror or lens system.

2. As a concave mirror is expensive, a cheaper equivalent made of a lens plus a mirror right behind it is often in use. This alternative is also lighter and more convenient to use than a thick lens in lighting cigarettes.

3. It has been carried out on a summer day with a lot of sunray heat per square meter area. The steady focussing is essential and the method may not be suitable on a unsteady platforms such as boats, ships, trains …

4. It has been carried out in a dry day.

5. The cuttings of leaves inside the cigarette (acting as fuel, tinder) should have dark colour to absorb sun ray heat

6. Gentle sucking is required to intensify a smouldering into a fire. Blowing air out from the butt of the cigarette may not intensify the fire.

7. To check the sphericity of the head of the spoon, you have to look at your own upside down reflection inside the spoon head. Till the spoon in various direction to have your reflection moved from the center to various sides on the edge. The spoon head is spherical if your picture does not expand or shrink during the test.

Some unusual sources of fire and unintended fire can be found in the references.

References.

[1]. Anonymous Author, Brigade step up sunlight warning after another refraction blaze, London Fire Brigade, http://www.london-fire.gov.uk /news/LatestNewsReleases_warningassunstunscelebrity.asp#.VndyHOW4ZAg, 26 February 2015.

[2]. PF Louis, Metal dog bowls can start house fires from focused sunlight reflections, Natural news , http://www.naturalnews.com/040979_dog_bowls_house_fires_&#8230; href=”http://www.naturalnews.com/040979_dog_bowls_house_fires_fire_prevention.html”&gt; http://www.naturalnews.com/040979_dog_bowls_house_fires_&#8230; ,June 28, 2013

[3]. Matt Payton, Jar of Nutella destroys family home and kills pet dogs, Metro.co.uk ,

http://metro.co.uk/2015/02/23/nutella-jar-helped-sun-rays-set-fire-to-family-house-and-kill-pet-dog-5076204/ ,23 Feb 2015.

[4]. Peter Lappin, Working on My Linen Shorts + How I Nearly Burned the House Down, Male pattern boldness, http://malepatternboldness.blogspot.com.au/2014/0&#8230; , Aug 18, 2014.

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Finding North direction and time using the hidden Sun via the Moon

Finding North direction and time using the hidden Sun via the Moon.

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(Blog No.006).

#find North, #finding North, #compass, #direction, #time, #Sun, #hidden Sun, #navigation, #survival, #Moon, #phase,

Finding North direction from the Moon cannot not be as accurate as from the Sun. There are many causes for this:
1/- The Moon does not always rise on the principal East (at 90 degree of the compass rose).
2/- We cannot work out by heart the Moon’s declination (up to +/- 5.1 degrees to the ecliptic, and 23.5+5.1 degrees to the Celestial equator ).
3/- We cannot easily work out when the Moon reaches its highest elevation angle at its meridian time. The Moon does not often cast strong shadows for shadow sticks to work.
Here I describe my new method to find out North direction and time with improved accuracy. The method uses shape and position of the Moon, solar declination and user latitude to work out the position of the hidden Sun, then work out North direction and approximate local time with an accuracy of 30 minutes. Literally, the user can work out North direction and the local time with his bare hands.
I have field tested this method and I have relied on it for many years.

1. Basic information on the Moon for navigation.

image

image

Figure 1: Moon phase chart. Figure 2: A crescent Moon may not align itself to the terrestrial East or West horizon points (see texts).

The Moon is a satellite of the earth. Everyday Moon-rise and Moon-set time is retarded by about 50 minutes. This allows the Sun to travel further on its journey every subsequent night. Therefore after full moon the partial bright side stays on the East (trailing) side and dark crescent appears on the West and dark area gets fatter daily until the whole moon is dark. Similarly, from new Moon a bright crescent appears on the West and grows fatter and bright area gets fatter daily until full Moon is reached. However the bright and dark sides of a partial Moon rarely point accurately to East or West directions.

Figure 2 of this section shows a crescent Moon on the Celestial sphere. The horizontal great circle represents the horizon of the observer. The inclined great circle represent the Celestial equator and the arrow through the center of the sphere represents the Celestial axis. The circle parallel to the Celestial equator is a constant declination circle being the trajectory of the Moon during the hours. The two intersection points of the two great circles are the terrestrial East and West points of the horizon. This picture shows that the crescent Moon may point its bright to dark line far away from the terrestrial East or West points when there is a combination of high declinations of both the Moon and the Sun on the same side of the Celestial equator.

Each Lunar (Moon) cycle begins with the Moon being visible as a thin bright arc in the sky (called a New Moon), trailing the Sun by less than one hour. After Sunset this thin Moon is seen bright on the West until it sets. On subsequent days, the Moon is more and more behind the Sun, its position shifts gradually towards the East and the Moon remains for longer and longer duration in the night sky till full Moon day. After full Moon day, the Moon (now called a Late Moon) becomes thinner and thinner and is seen risen in the East in the night, it remains visible in the sky after Sunrise, and travels ahead of the Sun. On subsequent days, its lead on the Sun gradually reduces. Near the end of the cycle, the Moon is visible as only a thin bright arc rising in the East for less than one hour before Sunrise and after Sunrise it can still be seen leading the Sun by that same amount of time. At the end of the Lunar cycle, the Moon sends no reflection of Sunlight to Earth and is too close to the Sun to be visible in the day sky.

Keeping diaries of past days of full and new Moon helps people know where their time is in the current cycle, and so they know whether the leading (West) side of the Moon should be bright (new to full Moon) or dark (full to new Moon). Fortunately, the users of my method described here do not have to refer to any such records of the Moon.

It is interesting to note that Buddhist East Asians use lunar calendars and observe fasting at new and full Moon. From their calendar and their fasting festivals , they already know whether the Moon is waxing or waning. This may help explaining why they are good at finding North direction using the Moon.

CAUTION 1: The bright to dark line of the partial Moon can point far away from the terrestrial principal East or West directions.

CAUTION 2: The horn line of the partial Moon can point far away from the terrestrial principal North or South directions.

2. Moon shapes giving Moon-Earth-Sun alignment.

The various shapes of the Moon under various angles of lighting by the Sun are given in the illustration picture. The Moon goes through this cycle every 29.5 days. The picture is drawn for the principal values of the angle of Moon-Earth-Sun. The picture allows determination of the direction of the Sun from the shape of the Moon.
The angle Moon-Earth-Sun will be more accurately known if the navigator is in the habit of directly measuring and recording it before Sunset (few hours earlier) whenever the Moon is seen during day light.

3: Direction of the Sun from the Moon

image

image

The line joining the two horns of the Moon is always at right angle to the plane of Sun, Earth and the Moon. Draw a half-line from you to the Moon and extending far past the Moon. Imagine the Sun is at the far end of this half-line. Swing this half-line in the direction of the bright side (at right angle to the line joining the two horns) of the Moon to have the angle of Moon, Earth and Sun giving a matching shape for the brightened part of the Moon. The half-line then gives the direction of the Sun.
Alternatively, you can think of placing a sphere between you and the Moon, and a torch is is used to shine on the sphere and the torch is placed in various directions until it gives a partially brightened sphere similar to the current Moon shape.

4. Finding North direction and time.

image

image

image

image

image

image

divider43.jpg

With the direction of the Sun known, the technique given by my previous blogpost “Finding North direction and time using the Sun and a divider” [1] can be applied to find North direction and local time.
The selection rule of right or left hand placement of CA in “Finding North direction and time ising the Sun and a divider” has been generalized.

The generalization is:
(Northern latitudes with rising Sun or Southern lat. with setting Sun) ==> CA on the left of CB,
(Northern latitudes with setting Sun or Southern lat. with rising Sun) ==> CA on the right of CB.
The time for rising Sun here is from 0hr to 12hr (AM) and time for setting Sun here is from 12hr to 24hr (PM).
The rest of that method applies to the hidden Sun to give North direction as well as time.

I have tested and found that this method gives direction accurately and easily. The additional benefit is that it also gives approximate time.

Reference
[1]. tonytran2015, Finding North direction and time using the Sun and a divider, http://www.survivaltricks.wordpress.com/, 06 May 2015.

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, posted on 2018 July 10

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Using polarized light to locate the Sun when it is hidden from view.

Using polarized light to locate the Sun when it is hidden from view.

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#find, #finding, #Sun, #North, #navigation, #survival, #find the Sun, #polarize, #light, #ray, #Sunlight, #Sunray, #sunglasses, #compass, #direction, #time

Anti-glare polarizing sunglasses reduce horizontally polarized rays. They can also be useful in locating the Sun even when it is hidden from view by clouds or by the horizon. Locating the Sun enables determination of compass direction and time for navigation without any compass.

1. Basic information

Two walkie-talkies are in the best condition for communication when their two antennas are parallel and at right angle to their line of view. The electric waves traveling between them have their electric field parallel to the emitting antenna and the varying electric field is at right angle to the line of transmission. The electromagnetic waves is said to be polarized in the direction of the emitting antenna.

Light is just electromagnetic waves at much higher frequencies than our familiar radio waves. Light can be polarized too. Light rays from incandescent sources are randomly polarized like radio waves coming from a walkie-talkie which is randomly orientated before each transmission. On the average we don’t see any polarization from a source with randomly changing orientation. However after a partial reflection (accompanied by a partial transmission) at an interface between two transmission media, the reflected and the transmitted rays from any non-polarized ray becomes partially polarized.

Polarizing sunglasses can favour light polarized in one direction and discriminate against light polarized in the other direction. With the same pair of sunglasses we can see two different colours and brightnesses depending on the orientation of the glasses when viewing the same source. This is illustrated in the following figure.

Be certain that your polarizing glasses really reduces sunlight reflecting off horizontal road surfaces before trying subsequent instructions here; each of the glasses must be individually tested and its direction of polarization verified.

2. Different colours and degrees of brightness seen from the same source of light through polarizing sunglasses

skylight through polarizing sunglasses

The cross with two different colours on the source denotes the two different colours seen through two orientations of the same sunglasses.

3. Seeing the polarized lights of the sky

polarization of scattered blue sunlight

The polarization of scattered blue sunlight in the sky

Blue light from the sky is the result of Rayleigh scattering of photons from sunlight by molecules in the sky. This scattered light is highly polarized as seen in the following practice:

Search for a large clear patch of sky with no cloud. Look through the polarizing glasses. Rotate the glasses about the axis of view to see the sky lightens and darkens alternatingly with the angle of rotation. The darkening is most profound when the Sun is at right angle to the line of view.

4. Locating the hidden Sun.

Locating the hidden Sun using polarized light

Locating the hidden Sun from two patches of clear sky.

1/- Search for a large clear patch of sky with no cloud. Rotate the glasses about the axis of view until the clear sky becomes most darkened. The Sun is then on the great circle perpendicular to the line joining the left and right spectacles (Being the intersection of the Celestial sphere and the symmetry plane of the sunglasses). The darkening is most profound when the Sun is at right angle to the line of view.

2/- Repeat with a second clear patch of the sky. Two large clear patches of the sky can give out the position of the hidden Sun. It is at the intersection of the two so obtained great circles in the sky.

3/- The position of the Sun below the sky-line can also be found using polarized light-rays from the clear sky above its (underground) line of view. If the illustration picture of this section is turned up side down with a horizon line added above its Sun it will illustrate how to find the Sun when it is below the horizon (The polarization is most profound on the clear sky at 90 degree to the (underground) line of view of the Sun.).

Reference [2] gives some interesting history of the early applications of polarization of light. Currently there have even been hypotheses that the Vikings had used polarized light to locate the Sun since antiquity with pieces of birefringent calcite crystals [1].

References.

[1]. Cahal Milmo, Not just the stuff of legend: Famed Viking ‘sunstone’ did exist, believe scientists,
The Independent, http://www.independent.co.uk/news/science/archaeology/not-just-the-stuff-of-legend-famed-viking-sunstone-did-exist-believe-scientists-8521522.html, 06 March 2013, 21 May 2015.

[2]. Unknown Authors, Polarization (waves), Wikipedia, http://en.wikipedia.org/wiki/Polarization_%28wave… 26 May 2015

[3]. Unknown Authors, Following the Light of the Sky, polarization.net, https://www.polarization.com/compass/compass.html… Accessed 16 May 2015 05:40:14 GMT.

[4]. tonytran2015, Finding North direction and time using the Sun and a divider, http://www.survivaltricks.wordpress.com/, 06 May 2015.

(The following is added after 20 May 2017)

[5]. Israel Ramirez, https://www.quora.com/What-can-animals-that-can-see-the-polarization-of-light-see-that-other-animals-cannot, 28 Nov 2016.

[6]. tonytran2015, Finding North in the polar zones using equatorial stars and the Sun, https://survivaltricks.wordpress.com/2017/05/24/finding-north-in-the-polar-zones-using-equatorial-stars-and-the-sun/, posted May 24, 2017,

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Finding directions and time using the Sun and a divider.

Finding directions and time using the Sun and a divider

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#find North, #finding North, #compass, #direction, #time, #Sun, #divider, #navigation, #survival, #bare hands.

There are times when you neither have your watch nor can use any magnetic compass in the location but you want to find out the time and the North-South directions. This method is useful for those such difficult situations. The divider or the dividing compass in the title of this article is actually not necessary, it is helpful but it only improves the accuracy of the method and can be replaced by any two straight sticks or even by your two stretched arms. Those situations are not very unlikely and one such situation may arise if you get lost without having your watch while traveling or if you find yourself without your watch while traveling inside a bus or a train. The method from this article gives both the North direction and the local time (local time starts its noon when the Sun is highest, local time is close to but is not the same as the official zonal time declared by the local government there.) from the position of the Sun in the sky, the latitude and the day of the year.

1. Finding North in 7 steps.

find North by a Divider

Figure: Finding North direction and local time with a divider (viewed against the Sun).

Find North by Divider

Figure: Finding North direction and local time with a divider (viewed against the Sun).

1.1/- Let the two legs of the divider be CA and CB. Let CA and CB of the divider form an angle ACB equal to that from the lower Celestial pole to the Sun. This angle is obtainable from the declination of the Sun and can also be easily worked out by the observer. (A divider or a dividing compass is a compass with two long legs having pointed ends. The lower Celestial pole is the Celestial pole below the ground plane of the observer.)

1.2/- Point the second leg CB of divider to the Sun. Rotate the divider about its second leg CB so that its first leg CA points slightly downwards to the ground, inclined to the ground by an angle equal to the local latitude while leg CB still points to the Sun.

1.3/- There are usually two such dipping positions for leg CA, each has its dipping angle equal to the latitude angle. Only one position for CA is the correct one.

Find North by Divider

Figure: Aligning the divider along the directions of Sun rays and the laying of compass points.

1.4/- The correct choice for the position of leg CA is given by the following rules: 4a/- At a Northern latitude and during sunrise half-day : Downward axis points (Southwards) to the left of the ray from the Sun. 4b/- At Noon: The two possible positions of leg CA coincide and there is only one single position for leg CA. 4c/- At a Northern latitude and during sunset half-day : Downward axis points (Southwards) to the right of the ray from the Sun. 4d/- On the other hand, at a Southern latitude and during sunrise half-day downward axis points (Northwards) to the right of the ray from the Sun while during sunset half-day it points (Northwards) to the left of the ray from the Sun. 4e/- Observer must be absolutely certain of being in which half (sunrise or sunset) of the day as any mixing up between the sunrise and the sunset halves of the day will give an error in direction of more than 90 degree. 4f/- The correct choice makes leg CA points downwards to the lower Celestial pole and leg CB rotates around leg CA exactly one whole turn every 24 hours. (Users can easily make up ways to remind themselves of the choice dictated by 4a, 4b and 4c.)

Find North by Sun and Divider

Figure: Finding North direction and time using the Sun and a divider.

1.5/- The terrestrial North-South is the projection of leg CA onto the ground surface. This method gives directions with an accuracy of better than 15 degrees of angle when the Sun is far away from the zenith of the observer.

Find time by divider

Figure: Reading time from the divider.

Sun on Celestial Sphere

Figure: Daily travel of the Sun on the Celestial sphere.
1.6/- Imagine having a 24-hr watch dial mounted onto the leg CA of the divider with the marking for 0th hour on the highest position. The local time is then given by the position of leg B relative to this imaginary dial. Time reading from the position of CB gives local time with an accuracy smaller than 30 minutes.

Find North by Sun n Divider

Figure: Summary of the steps for all solar position (above and below the horizon).

The author has been using his method for more than ten years and found it to be applicable, convenient and accurate for both Northern and Southern latitudes.

1.7/ If the Moon can be seen in day light, a navigator should continue from the so determined direction of the Celestial axis to measure the declination of the Moon and its angular distance from the Sun for that day. He can then continue his accurate determination of Celestial axis during the Moon lit part of the night by replacing the unseen Sun by the Moon together with its value of declination and angular distance from the Sun supplied by himself.

2.Cautionary notes.

C1/- Newcomers to this method should only practice it when the Sun has low elevation angle to get used to the right and left hand selection rules and to the judgement on the amount of dipping of the leg CA to find the Celestial axis.

C2/- People who fall asleep because of exhaustion or sickness may get confused between the two halves of the day on waking up and may make mistakes when using this method at that moment.

3.Explanation notes.

N1/- There are the North and South Celestial poles in the Celestial sphere. The line joining the North and South Celestial poles is called the Celestial axis. The lower Celestial pole is the one that is under the horizontal plane of the observer, therefore it can not be seen by the observer ! The Southern and Northern Celestial poles are respectively the lower Celestial poles of the Northern and Southern hemispheres of the Earth. The sunrise half-day is from midnight to noon (0 hr at midnight to 12 hr at noon). The elevation angle of the Sun increases during this time. The sunset half-day is from noon to midnight (12 hr at noon to 24 hr at midnight). The elevation angle of the Sun decreases during this time.

N2/- The Celestial axis for any location can be easily found by the following method: Have three similar thin sticks. Tie one of the ends of each stick to a common point P. Let the three sticks point respectively to the positions of the Sun at sunrise, sunset and noon. This can be easily done on any level sandy surface as two sticks can lay on the ground pointing from point P to sunrise and sunset directions while the third stick already has one of its ends resting on P on the ground and only needs small help to be kept in position. Let a sphere (e.g. an orange fruit or a soccer ball) with suitable size touch all three sticks at the same time (The surface may have to be dug around the sphere so that it can touch all three sticks at the same time.). The line joining P to the centre of the sphere is the Celestial axis.

Solar Declination versus time

Figure: Declination of the Sun from a rough graph.

N3/- The angle from the lower Celestial pole to the Sun varies like a sine wave with amplitude of 23 degrees 27minutes and period of nearly 365.25 days. It varies slowly and periodically during the year. It is the sum of 90 degrees and the declination of the Sun. The angle is exactly equal to 90 degree on Spring and Autumn equinox days (21st of March and 23 rd of September) It reaches a maximum value of 90+23.5 on local summer Solstice days (21st of June for Northern hemisphere and 21st of December for Southern hemisphere). It reaches a minimum value of 90-23.5 on local winter Solstice days (21st of December for Northern hemisphere and 21st of June for Southern hemisphere). Equinox and Solstice days of the years are the principal days for working out these values .

N4/- The markings on the dial of any analogue watch can be used to measure the angles used for the divider. Any quarter of the watch dial gives an angle of 90 degrees. One hour marking on any 12-hr watch therefore gives an angle of 30 degrees.

N5/- A watch face can be drawn on the ground to obtain more accurate value of solar declination as in the following figure (see reference [1]).

solar-declination-by-a-watch-face

Figure: Determining solar declination using a watch face. (The lines “SOLAR DECLINATION Its rough estimate is required for Fine Alignment of the watch” are to be ignored.)

4.Additional notes.

image

Figure: Improvised instructional divider made from a stylish, pen-styled compass by extending its legs using plastic drinking straws.

The instructional divider is built from a pocket, pen-styled (Vietnamese, Thien-Long brand) compass. The two legs are extended by pushing two plastic drinking straws (in yellow colour) onto the cylindrical ends of the compass. Fortunately, the fit is just right. The device works very well and costs me under $3USD !

References (added 09 Mar 2017)

[1]. tonytran2015, , survivaltricks.wordpress.com, posted on February 13, 2017

[2a]. (same topic on youtube) https://www.youtube.com/watch?v=iWgqO9CsQvU&t=58s

[2b]. (same topic on youtube) https://www.youtube.com/watch?v=noo2OoJ84tU

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image

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