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

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Navigating with an AM MW radio receiver

Navigating with an AM MW radio receiver

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.48).

#AM, #broadcast, #emergency, #radio, #radio direction finding, #find North, #Medium Wave, #radio navigation.

Every natural disaster emergency kit is recommended by authorities to include a battery operated Amplitude Modulation Medium Wave (AM MW, also called AM Broadcast) radio receiver to receive critical information and instructions.

The radio receiver can actually do much more than receiving information and instructions. It can find the direction to nearby AM broadcasting stations and even find your location on any map showing the stations.

Figure: Map of Melbourne with 2 nearby AM broadcasting stations shown as red dots. Map has been modified from original map used under Open License from Open Street Map, the data are owned by Open Street Map Contributors.

The technique is applicable when there are nearby (closer than 100km) AM broadcast stations. It is useful to regions near the terrestrial magnetic poles where magnetic compasses do not work well, to desert crossing and to coastal boat travel when visibility is very poor and other modes of navigation are not available (such as when in bad or extreme weather, during volcanic emergency and without any working magnetic compass).

1. Basis of Radio-direction-finding.

An AM broadcasting station in Medium Wave sends electromagnetic waves out from its antenna at the speed of light. The invisible EM waves propagate outwards from the broadcast station’s vertical antenna. The antenna continuously releases consecutive, expanding circular magnetic lines of alternating (clockwise then anti-clockwise) orientations. The circles spread out in all directions. When a receiver receives the signal, the alternating magnetic field is at right angle to both the spreading (propagation) direction and the alternating electrical field which is almost in the direction of the broadcasting antenna.

Most AM radio receiving Medium Waves (0.5MHz to 1.6MHz) use ferrite rod antennas to capture these magnetic field lines. The ferrite rod of an AM MW receiver is usually placed inside and along the top edge of the (usually flat) receiver. Figure 4 shows the ferrite rod antenna inside a Sony radio of a common design.

sharp radio

Figure 1: A battery operated multi-band AM radio that can be used in emergency. This battery operated multi-band AM radio with a fair sized signal strength indicator in a small window on the left of the dial was made in the 1960’s. Its pulled out rod antenna is only for Short Wave reception, an internal long ferrite rod antenna is used for Medium Wave reception.

radiosony

Figure 2: A compact radio receiver WITH an AM internal ferrite rod antenna that can be best for emergency use. This compact AM/FM receiver has an internal ferrite rod antenna for AM MW reception and can properly receive AM signals even without using any earphone.

When an AM MW (also called broadcast band) radio receiver has been tuned to a station, you can notice the signal strength varies when its ferrite rod antenna is rotated on the horizontal plane: The received signal is weakest when either end of the rod is pointed directly at the transmitting station, and it is strongest when the rod is at right angle to the line of sight to the station. The technique has been widely used for ships until the advent of low cost GPS. Reference [1] gives a really interesting long list with pictures of AM radio receivers specially built for the application of this technique on ships.

Figure 3: A 3 band Sony transistor radio with a retractable short wave rod antenna (radio model 838, assembled in South Vietnam in 1970, under license from SONY, as shown on the label on the back of the radio).

direction by ferrite rod antenna

Figure 4: The interior of the Sony transistor radio showing a long ferrite rod antenna of grey colour on the top and parallel to the top edge. (Sony radio model 838, assembled in South Vietnam in 1970, under license from SONY, as shown on the label on the back of the radio.)

CAUTION: Many compact AM MW radio receivers do NOT have ferrite rod antennas, they use their earphone wires to receive the electrical component of the broadcast waves. This method of finding directions does NOT work with such receivers.

2. Finding direction by a radio.

Rotate the top edge (with the ferrite antenna) of the receiver by a full horizontal turn and notice the two opposite directions where signal receptions are weakest. When this happens, one of the ends of the ferrite rod is pointing exactly at the station and the station lies on the line through the top edge of the receiver. Additional information from somewhere else is needed to tell in which of the opposite directions the station may lie.

Figure: Openstreetmap for Melbourne with added cooodinates and the locations of Delahey and Lower Plenty. Map has been modified from original map used under Open License from Open Street Map, the data are owned by Open Street Map Contributor.

Examples:

a. “ABC Radio Melbourne ‘s 774 kHz transmitter is located in Delahey (the left red dot in the map), 20 km north-west of Melbourne’s central business district. … at a power of 50,000 watts,… one of two transmitters using the callsign 3LO” [2].

When an AM radio is tuned to 3LO on 774kHz it receives the broadcast with call sign 3LO. When its ferrite antenna is pointed at the left red dot on the map, the signal will be weakest and the reception most noisy.

b. ABC NEWS on radio ABC NEWS on radio Frequency 1026 AM Callsign 3PB Sound Mode Mono Polarisation Vertical Broadcast Pattern OmniDirectional Transmitter Location Bonds Road LOWER PLENTY (the right red dot on the map)” [3].

When an AM radio is tuned to 3PB on 1026kHz it receives the broadcast with call sign 3PB. When its ferrite antenna is pointed at the right red dot on the map, the signal will be weakest and the reception most noisy.

You may be able to find the frequencies and transmitter locations of the AM broadcasts for your area from the useful sites [4] www.dxing.info, [5] wiki List of European medium wave transmitters

3. Finding location by a line through the station.

If the direction of the top edge of the receiver relative to true North is known, the locus of the receiver on the map is a straight line through the broadcasting station.

Your location can be found using the intersection of two such locus lines through two broadcasting stations shown on a map. (The intersection R of the lines RS1 and RS2).

4. Finding location by a circle through two stations.

If two stations S1 and S2 are shown on a map and A is a directed (signed) angle from the line to S1 to the line to S2 then the locus of the radio receiver is the circle through S1 and S2 bearing that directed angle A.

For example, if the angle from R-S1 to R-S2 is 40 degrees (an example value) in the anti-clockwise direction, the receiver must be on the red circle drawn through S1 and S2 on the map. The example circle is called the circle bearing the angle of 40 degree in the anti-clockwise direction for viewing the (direcred) line segment S1-S2.

5. Finding location by three circles through three stations shown on a map.

arc bearing

Figure 1: Finding your location using intersecting angle bearing circles.

Any map showing the locations of the broadcasting stations S1, S2, S3,… can be used to locate the position R of the radio receiver. Any receiver with the angle from R-S1 to R-S2 being 40 degrees clockwise (an example value) in the clockwise direction must be on the circle drawn through S1 and S2 for that example value of 40 degrees. The example circle is called the circle bearing the angle of 40 degree in the clockwise direction for viewing the line S1-S2.

If three stations S1, S2 and S3 are shown on a map as in the figure of the last section and the directed (signed) angles between the directions to S1, S2, S3 are all known, the receiver is on the intersection of all three circles through each pair of S1, S2 and S3 bearing the respective directed angles between them. Usually, only two circles are needed to draw the intersection point, which is the location of the radio receiver R.

6. Limitation of the method.

a. The method works well if there are non-interfering AM broadcast stations within 100km of the navigator and the terrain is nearly flat.

b. When there are high atmospheric electrical activities it may be hard to find the direction for weakest reception by the ferrite rod of the broadcasting signals.

c. Many compact AM MW radio receivers do NOT have ferrite rod antennas, they use their earphone wires to receive the electrical component of the broadcast waves. This method of finding directions does NOT work with such receivers.

d. The method does NOT work with Shortwaves as shortwave signals are not received through ferrite rod antennas.

e. Note that Philips from Holland had a famous radio model, L4X00T, with a fold up/fold down rectangular antenna loop for shortwaves, which can also be used to find out the direction of the incoming shortwaves in the same way as described in preceding sections. However shortwaves bounce and they do not accurately show the directions to the stations.

f. For the method to be useful after an Electro-Magnetic-Pulse event, the receiver and the broadcasting stations should all survive the event. You may have to wrap your radio receiver in many layers of Aluminium foils and the broadcasting stations must know how to protect themselves against EMP events.

Reference.

[1]. Radio Direction Finders, angelfire.com, http://www.angelfire.com/space/proto57/rdf.html, accessed 06 Feb 2017.

[2]. https://en.m.wikipedia.org/wiki/ABC_Radio_Melbourne

[3]. http://www2b.abc.net.au/reception/frequencyfinder/asp/details.asp?transmissionid=2956.

[4]. http://www.dxing.info/lists/

[5]. https://en.m.wikipedia.org/wiki/List_of_European_medium_wave_transmitters

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The Scorpius constellation

The Scorpius constellation

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.45).

#find North, #finding North, #direction, #by stars, #Scorpius, #Antares, #Sagittarius, #Ara, #navigation, #constellation.

Celestial navigators who do not use declination and right ascension begin their navigation by learning the various bright, easily identifiable constellations in the sky (There are no more than 10 to learn.). The Scorpius is usually chosen to be the second constellation to be learned since it is as large as Orion and is useful when Orion is out of sight.

The Scorpius is a crowded, large Southern constellation of June. Part of it is always seen in the sky of June for the whole night, attains its highest elevation (or altitude) about midnight and is immediately South of the most Southern point of the Ecliptic. Scorpius can be seen on the rising side before sunrise in January, seen for the whole night in May and seen on the setting side after sunset in November.

It has the size of 30 degree (in angle) and has the shape of a hook oriented 55 degree clockwise from the great circle arc through the Celestial poles. Arabian sky watchers see a resembling to the body and tail of a (now declawed) scorpion and gave it the name Scorpius.

The brightest star of Scorpius is Antares but it is so close to the ecliptic that it is often outshone by the Moon and bright planets traveling on the ecliptic. Antares often requires extra care for proper identification. Identifying Antares give a good practice to star identifying.

1. The Scorpius on a Mercator sky-map.

mercator8gc30.jpg

Figure 1: The Scorpio constellation is in the shape of a hook, is close to the ecliptic and one third from the left edge of this Mercator sky-map.

Figure 2: A common Asian scorpion.

The Scorpius has too many stars and its brightest star Antares can even be over-shone by planets wandering near to it. Therefore its identification often requires additional care.

An observer in the Southern hemisphere can check that the hook shaped stinging tail of the Scorpius is just touching the great circle arc (drawn in yellow) through the two Pointers to the Southern Cross.

Figure 3: The Scorpius is seen as a hook in the top left quadrant of this Polar Inversion map of the Southern hemisphere. Its hook shaped stinging tail is just touching the great circle arc (drawn in yellow) through the two Pointers to the Southern Cross.

2. An alternative method of recognizing stars in the Scorpius

Figure 1: Scorpius Sagittarius and Ara are easily recognized together.

I found that it is easier to recognize the bright stars of three constellations Scorpius, Sagittarius and Ara together. They resemble a tree with two side roots rising at right angle from a ground line.

The two brightest stars of all three constellations are Antares and Shaula in the Scorpius.They are separated by 17 degrees in angle. They line up with two other dim stars to form a straight line (delta Scorpius, Antares, Shaula and kappa Scorpius) which is slightly longer.

The South-trailing end of this line continues to be the bisector of a right angle line formed by five stars zeta Sagittarius, Kaus Australis, Shaula, theta Scorpius, alpha Ara.

The line of two brightest stars looks like a tree sticking up at right angle to the ground line formed by dimmer stars in line with alpha and epsilon Ara. The tree has two side roots (Shaula-Kaus Australis. and Shaula-theta Scorpius-alpha Ara) originating from Shaula and each is at 45 degree from the tree trunk.

After the bright stars have been identified, each constellation can be identified using its conventional map as given in [1] and [2].

3. Taking photos of the Scorpius.

The Scorpius is adequately bright and its photos can be taken using a smart phone such as a Samsung Galaxy Note 2 with no extra attachment.

Figure 1: A photo of the Scorpius Constellation taken with a Samsung Galaxy Note 2. This photo was added on 2018Feb26 and has been digitally enhanced.

The Scorpius constellation is in the center of this picture. There are four brightest dots on the top half of this picture. The far right and far left dots are very bright and are two planets traveling on the ecliptic. The planets on the ecliptic sometimes make it hard to identify this constellation. (This added photo was taken on 2018 Feb 26).

Scorpius

Figure 2: Photo of the Scorpius Constellation taken with a Samsung Galaxy Note 2. The original photo was taken prior to 2017Jan09 and has been digitally enhanced.

Scorpius

Figure 2: Another photo of the Scorpius Constellation taken with Samsung Galaxy Note 2. The original photo was taken prior to 2017Jan09 and has been digitally enhanced. There are three bright dots in a straight line at the top of the first photo. The two on the left are two planets on the ecliptic. The third one on the right is delta Scorpius. Antares is the bright dot under the three in line.

4. Easy identification of Scorpius by a slide sky map.

starmap18april0130c.jpg

Figure 1: The Scorpius position by the Mercator slide sky map, with an altitude grid for an observer on 10 deg North (South of India, Thailand, Malaysia, South of Vietnam, the Phillipines, Central America) .

Observers who are not quite familiar with the Scorpius constellation can use the slide sky map described in reference [2] to confirm its identity. The latitude of the observer, time, and North direction are required for identification using a slide sky map. The figure here gives its altitude (elevation) and its orientation at the time of the first photo of the preceding section.

References.

[1]. tonytran2015, Finding North and time by stars in the tropics, survivaltricks.wordpress.com,Finding North and time by stars in the tropics, posted on May 25, 2016

[2]. tonytran2015, Slide Sky-Map for displaying tropical stars, survivaltricks.wordpress.com, Slide Sky-Map for displaying tropical stars., posted on October 7, 2016

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

[4]. The Orion constellation., posted December 26, 2016

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The Orion constellation.

​The Orion constellation

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.43).

#find North, #direction, #by stars, #Orion, #Sirius, #navigation, #constellation.

Celestial navigators who do not use declination and right ascension begin their navigation by learning the various bright, easily identifiable constellations in the sky (There are no more than 10 to learn.).

The Orion is usually chosen to be the first constellation to be learned. The Orion is a bright, easily identifiable constellation of December. It stays in the sky of December for the whole night, attains its highest elevation (or altitude) about midnight and is right on the Celestial equator.
It has the size of 30 degree (in angle) and has the shape of a waisted rectangle. Western sky watchers see a resembling to man in an armor vest and gave it the name Orion. Pacific sky watchers see its two brightest diagonal stars as the ends of a large stick in the sky.

It is never blinded by the Moon or any bright planet as the ecliptic is well away from it. As it is quite bright and has easily identifiable shape, it is usually used as the base (anchor marks) to start locating other stars.

1. The Orion on a Mercator sky-map.

mercator8gc30.jpg

Figure 1: The Orion constellation is right on the Celestial Equator and one third from the right edge of this Mercator sky-map.

 



The three dim stars in a straight line starting from the waist band and almost at right angle to it (not shown in this simplified Mercator sky map) are called the Dagger stars. The Dagger is at right angle to the Celestial equator and points along a great arc in the North to South direction on the Celestial sphere.


Rigel or Beta Orionis is bright star at the South leading corner of the waisted rectangle. Betelgeuse is bright star at the North trailing corner of the waisted rectangle. Bellatrix is a less bright star on the North leading corner of the rectangle.

Rotating the line Betelgeuse – Rigel by 90 degree in the anti-clockwise direction gives the line Betelgeuse – Aldebaran, (Aldebaran is also called alpha Tauri).

Extending the line Bellatrix-Aldebaran by another 50% makes it reaches Pleiades group of stars (not shown on this simplified Mercator sky map). This group has millions of stars fitting within an area as small as the area of the Moon (The area is equal to that of a fingernail on a fully extended arm). Most people can see a brush shape made of 7 brightest stars of this group.

On the trailing side of Orion lies the brightest star in the sky. It is Sirius. Rigel -Betelgeuse – Sirius form an almost equilateral triangle on the trailing side of the line Rigel – Betelgeuse.

Betelgeuse is the star of December 20th and the December solstice occurs on the 21st of December, on the following night .

The night when the brightest star Sirius attains its highest altitude at midnight is the first night of a new (Roman) calendar year (Is it a coincidence?).

2. Taking photos of the Orion.

Orion Constellation

Figure 2: Photo of the Orion Constellation taken with a Samsung Galaxy Note 2. The original photo has been digitally enhanced. Sirius is the brightest star on the lower half. Rigel, Betelgeuse and gamma-Gemini are in line (from bottom to top) and almost equally spaced.

Figure 3: Photo of the Orion Constellation taken with a Samsung Galaxy Note 2. The original photo has been digitally enhanced. On this night there was a bright object (planet ?) on the elliptic near to the leading shoulder of Orion.

The Orion is quite bright and photo can be taken using a smart phone such as a Samsung Galaxy Note 2 with no extra attachment.

Notes: The photos have been updated in March 2018.

References.

[1]. tonytran2015, Finding North and time by stars in the tropics, survivaltricks.wordpress.com, Finding North and time by stars in the tropics, posted on May 25, 2016

[2]. tonytran2015, Slide Sky-Map for displaying tropical stars, survivaltricks.wordpress.com, Slide Sky-Map for displaying tropical stars., posted on October 7, 2016

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

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, posted on Circumpolar Stars Nth

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scorpiussaggigridaltc30.jpg20160418_013006enhenc2c30.jpg

posted on October 21, 2016

antare4smallc30.jpgfomalhautsmallc30.jpgariessmallc30.jpg

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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Using GPS in off-grid situations.

Using GPS in off-grid situations

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.36).

#find North, #tine #GPS, #GPS altitude, #GPS coordinates, #GPS navigation, #off grid, #topographic map, #longitude, #latitude,
Locating where you are using the internet is great but there are times when you have no mean to connect to the internet and you have to use GPS for positioning without any assistance via the internet.

Such a situation may arise when you have no internet coverage such as when going hiking.

This posting shows how to do it with minimum battery use.

1. Requirements:

a. A phone with GPS hardware preferably with back up battery or re-charger.

b. A procedure to minimize battery usage.

c. A map with longitude and latitude coordinates printed on paper or stored in the phone (Section 8 will show how to draw those lines on any paper map).

d. An optional software to display your position on the map.

Map with Coordinates

Figure: Openstreetmap for Melbourne with added cooodinates. Map has been modified from original map used under Open License from Open Street Map, the data are owned by Open Street Map Contributors.

2. Selecting a phone with good off-grid GPS capability.

I would choose one that can quickly obtain an accurate GPS value from cold start. Different phoneMarkingsand GPS apps have different sensitivities, algorithms and accuracy.

Compass app and barometer app are highly desirable additions on such a phone.

Compass app using magnetic sensors gives you the direction without having to move at speed to obtain the deduced True North.(GPS apps obtain True North using solely the tiny increments from GPS coordinates). You should know how to calibrate a magnetic compass app by the figure 8 motion.

Barometer app gives your accurate altitude change if you need that value for working out your position using angles and changes in altitude. Barometer app can also warn you of developing severe weather.

3. Two different pieces of hardware can give out two different GPS readings.

The following are the readings from two different smart phones placed in one place. The readings have differences of about 4m in distances in both longitude and latitude directions. (Each minute of latitude angle is one nautical mile, and each second of latitude distance is about 3m in length).

Fig 1&2: Readings from the first smart phone.

Fig 3&4: Readings from the second smart phone running the same app at the same place!

The hardware is guaranteed to give you only some accuracy. My two smart phones seem to have horizontal accuracy values of no better than 4m. Their vertical accuracy values are not better than 10m.

4. A single point may correspond to different latitude and altitude values depending on the different base surfaces used for mean sea level.

Remember that the earth is not a perfect sphere. Its rotation and non-uniform interior density creates its non-spherical surface at sea level. Vertical lines do NOT converge at the center of the earth but are only the lines at right angle to the local sea surface. The latitude and longitude of a point as determined by sextants only give the direction of its vertical line, not the intercept between the non-spherical surface and a line from the center of the earth pointing in that direction!

With that idea in mind, it is clear that a single point in space may have different latitude and altitude values depending on different type of non-spherical surface used for mean sea level.
So you should choose apps with a widely accepted base surface (such as WGS84) so that their latitude and altitude values are readily interchangeable.

Figure 5,6: Reading from GPS Test (1.3.2).

Fig 7: Reading from GPS Status (5.3.112) on the same smart phone. The two apps give matching readings.

5. When communicating your coordinates with others, you may have to mention the name and version number of your GPS app or the type of base surface in use!

For the same reason, the 3D coordinates from your GPS apps may be inconsistent with the published coordinates of international airports or the land marks on your trips.

Any map with GPS capability such as Googlemap should be already compatible with its GPS in use.

6. Using AGPS updates to save battery.

The phone app can only listen to one GPS satellite at a time. There are many of them and only four clearest transmissions are useful (The others are either out of view or do not provide positional precision). To listen to every transmission and select the clearest four takes time. Then starting from the far off position will take a lot of time for the calculation algorithm to arrive at the correct GPS position.

Remember that the more time you have to wait for a GPS fix the more you run down your battery.

AGPS (Assisted GPS) provides the app with the list of the best transmissions to listen to (from your approximate position) and the algorithm will begin from your approximate position. You will save a lot of time and battery. Choose a GPS app with off-line AGPS update as your principal GPS app.

7. Procedures to use GPS apps

a/- Beware of the high battery usage by GPS hardware.

b/- Run your magnetic compass calibration apps if you think that compass directions may be required.

c/- Run your principal GPS app (with off-line AGPS update capability). Once a fix has been obtained update its AGPS immediately; this saves battery on future fixes.

d/- Run any other GPS apps with your desired features (such as inclination, altitude, magnetic heading, light meter, etc…) immediately after the principal one. The hardware can continue from the values previously obtained by your principal GPS app.

e/- TURN OFF the GPS hardware.

f/- Relate your GPS position to the coordinates (longitude and latitude and possibly with altitude) on the printed map or the map stored in your phone.

g/- Know the horizontal and vertical error of each fix to know your PROBABLE position.

h/- Turn off the phone or put it in stand-by mode to save battery.

8. Making a map graduated with Longitude and Latitude Lines.

1. Choose a map with your required resolution and range. The resolution differs for different application: For city street maps resolution should be better than 2m, for country town maps, resolurion only need to be better than 5m as houses are widely separated, for touring, exploring maps, resolution can be upto the (1/10) of the visual range, etc…

Figure: Openstreetmap for Melbourne with 3 airport landmarks. Map is used under Open License from Open Street Map, the data are owned by Open Street Map Contributors.

2. On that map, find some unmistakable features such as a well known Airport or Helipad, a Light House, a TV Transmission Tower, a Town Hall, Churches, Schools, Cottages in a forrest, sharply defined mountain peaks, trail intersections… with known longitudes and latitudes. Their coordinates are usually given on the Internet or or easily extracted from Google Map or Navigating Apps.
Find four such fearures located near the four extreme corners of your map. They will be used as your four land marks.

Ecample:

The 3 landmarks in use here are:

a. Melbourne Tullamarine airport, Elevation AMSL 434 ft / 132 m, Coordinates 37°40′24″S 144°50′36″E

b. Melbourne Moorabin airport, Elevation AMSL 50 ft / 15 m, Coordinates 37°58′33″S 145°06′08″E

c. Melbourne Essendon airport, Elevation AMSL 282 ft / 86 m, Coordinates 37°43′41″S 144°54′07″E

3. On a separate fresh sheet of paper make a coordinate grid of longitude and latitude covering your range.
On this sheet with grid but no map, mark the coordinates of your four land marks.

Figure: Melbourne Tullamarine and Moorabin airports on a grid map.

4. Check that the shape of the quadrilaleral formed by the four land marks is similar in both the grid sheet and the map. You map have to stretch or shrink the grid vertically and then horizontally to have a fit. The quadrilaterals should be similar if no mistakes have been made. If the shapes are similar you can proceed to the next step.

5a, If the map and grid are both digital, they can be superimposed to produce the final map:

Figure: Openstreetmap for Melbourne with added cooodinates. Map has been modified from original map used under Open License from Open Street Map, the data are owned by Open Street Map Contributors.

5b. If you are using printed map: Join two distant landmarks on the coordinate sheet and notice where the lines of “second of longititude” and of “second of latitude” intersect it

6. Reproduce that line, with all its intersecting points, on the actual map.

7. From these intersecting points project corresponding vertical lines to make the “second of longititude” lines and horizontal lines to make “second of latitude” lines.

8. Your map is now graduated with longitude and laritude lines.

9. Using GPS with maps.

I prefer to use topographic maps with old fashioned land marks (such as churches, tall towers …). Topographic maps give the additional constant ground altitude contours (relative to some mean sea level surface). Constant altitude curves are the faint brown curves on the map illustrated here. The height of each contour is given by a small number. The altitude values of 20m and 10m have been highlighted in this example map by two red circles.

Figure: Opentopomap for the area in my test. Map is used under Open License from Open Street Map, the data are owned by Open Street Map Contributors.

If you want to use your GPS with any map, you need to draw on top of it an accurate system of regularly spaced longitude and latitude coordinate lines as instructed in Section 8.

You can download a topological map of your area to practice drawing the coordinate lines, the constant altitude lines and learn about the accuracy of the values of longitude, latitude and altitude given by your GPS apps.

10. Integrated GPS and map apps.

GoogleMap is one such app. It automatically supply you with a map and works out your position from its included GPS. It is great when you are connected. Some old versions of Googlemap allow you to store a map of an area of about 30kmX30km for off-grid use. I don’t know if you can store maps for much larger areas.

I would keep a printed map with coordinates for back up when going off-grid since I would not put everything into one smart phone.

11. Error from GPS is rare but not impossible.

As with anything, continuity (or consistency) of readings must always be applied to check for any sudden error arising. It has been reported by BBC news that during the decommission of the GPS satellite SVN23, “some GPS positioning would have been thrown off by nearly 4km.”.

References

[1]. tonytran2015, Measuring angles and distances for outdoor survival, survivaltricks.wordpress.com,

https://survivaltricks.wordpress.com/2016/06/29/measuring-angles-and-distances-for-outdoor-survival/, posted 29/6/2016.

[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]. , BBC News, UK radio disturbance caused by satellite network bug,

http://www.bbc.com/news/technology-35463347, 2 February 2016.

Added after 2018 July 17:

[4]. https://irishinfosecnews.wordpress.com/2018/07/17/how-to-spoof-someones-gps-navigation-to-send-them-the-wrong-way/

Added after 2018 Nov 26:

The Thors’ son urged people travelling to remote locations without mobile coverage to download a GPS application to their phones ahead of their journey, as well as an offline map for their destination.

[5]. https://mobile.abc.net.au/news/2018-11-26/german-tourists-died-central-australia-walked-17km-heat-stress/10554408

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Identifying moderately bright navigational stars.

Identifying moderately bright navigational stars

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. 27).

#find north, #navigation, #survival, #moderate stars, #bright star, #Antares, #Fomalhaut, #direction, #distance, #great circle, #navigation, #stars, #neighbour stars, #sky map

Introduction.

Some navigational stars are only moderately bright although they are in the top 20 brightest stars. Antares and Fomalhaut are two such stars. They are used for navigation from September to November but are not easy to identify among their nearly as bright neighbours. The method for identifying them is to relate them to brighter neighbours which have been identified in previous periods of the year.
(GPS navigation cannot be relied on during periods of uncertainty. Traditional methods of navigation is still a necessary skill.)

Using an identifying map.
Knowing the date or even only the month of a star help locating parts of the sky where it may be found. The map giving distances and angles to its more distinctive neighbours then help its identification.

The maps are to be held such that its shown Celestial pole is pointing close to that actual Celestial pole whether it is in the sky or below the ground. The map is thus to be held in the star direction but oriented either upright or up-side-down.

Examples:

Figure 1: Antares in Scorpii with its neighbours. The centering mark is the Southern Celestial pole.

Figure 2: Fomalhaut with Alpha, Beta Grus and their neighbours. The centering mark is the Southern Celestial pole.

ariessmallc30.jpg

Figure 3: Hamal in Aries and its brighter neighbours. The tail of the inverted Little Dipper in the North is the North pole.

The first two maps make easy the confusing identification process of these two Southern navigational stars for October.

The third map makes easy the identification process of the dim Northern star Hamal in Aries for November.

References.

[1]. 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

[2]. tonytran2015, Finding North 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.

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Slide Sky-Map for displaying tropical stars.

Slide Sky-Map for displaying tropical stars

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, #direction, #time, #by stars, #Mercator, #sky map, #star map, #slide sky map, #navigation, #tropic, #declination, #right ascension.

slide sky map

Figure 1: Illustration of the Slide Sky-Map using the mask for 15 degree North latitude.
Slide Sky-Map for displaying tropical stars (blog No. 26).

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It is an advantage to know the arrangement of stars for the nights before engaging in nightly activities such as going to the country side or navigating your way by stars. It is difficult to have a good display of the tropical night sky with current commercially available circular star maps as they have a lot of distortion for tropical visualization whereas easy visualization requires that groups of stars should appears with the same shape as actually observed in the sky and the constant altitude curve should be nearly circular around the zenith point.

The device given in this posting gives the desired displays with low distortion for the tropical night sky and has been designed for use with latitudes between the two tropical lines. I give it the name Slide Sky-Map (which is similar to the name Slide Rules of similar looking mathematical devices before the age of calculators).

It is made of Mercator map of stars and of the viewing grids to give elevation and azimuth angles of stars to observers located near to 0 degree, 15 degree North and 15 degree South in latitude.

It will be useful to tropical people who want to learn the stars by themselves or need to refresh their nightly knowledge of the sky before going out. It is inexpensive, light weight, small, flexible, durable and quite portable. If made from waterproof materials, it may also be used as a low cost standby star map for travelers, hikers and seamen traveling in the tropic (my is made from waterproof sheets).

The device is made by following instructions in the next 4 steps. PLEASE READ THROUGH ALL STEPS BEFORE STARTING ANY CONSTRUCTION.

1. Making the maps for the core.

mercatorx1p6

Figures 1a: The Mercator map for the front of the core of the Slide Sky-Map.
star map mercatorx1p6

Figures 1b: An alternative Mercator map with star names for the front of the core of the Slide Sky-Map

mercator8fx1.6polarc30.jpg

Figures 2: The map on the reverse side of the core.

The map on the front of the core of the slide sky-map is a Mercator map with continuation by its repeat copy. The map here wraps around the Celestial equator by 600 degrees, meaning that it has about 1.7 times the width of the minimal Mercator map. The extra length allows the slider covering 180 degree in the East-West direction to be centered on any given longitude.

The two inversion maps of the North and South polar regions of the Celestial sphere are overlaid at the two ends of the same Mercator map and the combined map is placed on the reverse side of the core. The two insets represent the two polar regions of the Celestial sphere not displayed on the Mercator map. They help visualizing the two polar zones of the Celestial sphere, they can be easily joined to the polar sides of the Mercator map using shared common constellations present in both types of maps as stitching guides.

The core maps are to be printed on both sides of a thick sheet of A4 waterproof paper. This thick sheet of paper forms the core fitting inside the sleeves of next few steps. Alternatively the core maps can be printed on waterproof A4 papers and glued onto the opposite sides of a piece of thick waterproof board used as the core.

 

2. Making azimuth and elevation masks for the slider

mercator grid 00deg mask

Figure 1: The grid mask for 0 degree latitude.

mercator grid15d N.jpg

Figure 2: The grid mask 15 degree North latitude.

mercator grid 15d S.jpg

Figure 3: The grid masks for 15 degree South latitude.

A grid mask is placed on top of the core map to read the azimuth and the elevation of the stars drawn on the map. An observer must use the mask drawn for his latitude.

Description:
The smallest circle of each grid is graduated into 12 intervals of 30 degrees each to show the azimuth angle of the star or direction from True North. The curves radiating from the center represent the great circles from the zenith to the terrestrial points of 0 degree (North), 30, 60, 90 degree (East) , 120, 150, 180 degree (South), 210, 240, 270 degree (West), 300, 330. The concentric nearly circular curves represent the constant elevation circles in the sky. They are placed at 30, 60 and 90 degrees from the zenith. The curve at 90 degrees from the zenith represents the horizon on flat locations. The graduation can also be read from the horizon circle toward the center to show the elevation angle of the star. The position of any star in the sky can be read against the grid.

There are 3 grid masks given for this design. Select one that is based on a latitude nearest to your current latitude.

For latitude between 8 degree North and 8 degree South select the mask based on 0 degree latitude.

For latitude between 7 degree North and 23 degree North select the mask based on 15 degree latitude North.

For latitude between 7 degree South and 23 degree South select the mask based on 15 degree latitude South.

You can make all three masks as each can be easily fit into and removed from the device as you move to a location with a different latitude.

Make each mask with the CORRECT size and print it at the CENTER of an uncut A4 transparent sheet. Print the selected grid on a waterproof transparent film by a photocopier. If this cannot be done you may have to print the mask on an ordinary piece of paper, place a transparent film on top of it and trace the grid lines onto the waterproof transparent film using a pen with waterproof ink.

3. Making the slider (improved design, 2017, August 31).

slideskymap00

Figure 1: Photograph of an actual Slide Sky-Map fitted with the mask for the equator.

BrightStars20Plus2

Figure 2: Table of bright stars for the back side of the double layered slider sleeve.

Figure : The Mercator map of the sky for inhabitants of Tropical Zone. North direction is on its top. 24hr of R.A. is near the right side and R.A. increases towards the left (East) of the map.

The slider consists of a double layer white sleeve fitted with a transparent rectangular strip carried between its front layers.

Wrap a waterproof, white, thick sheet around the rectangular core map to make a white sleeve of no less than 360 degree along the East West direction of the core map (that is wrapping no less than two third of the length of the core map). The core should fit snugly inside the white sleeve and should be able to slide smoothly along its East West direction inside the white sleeve.

Cut a rectangular window on the front center of this white sleeve to reveal 180 degree width of the core map. The back of this white sleeve should be glued or taped to make it a proper sleeve.

Wrap another layer of the same waterproof, white material around the inner sleeve just made to make a white outer sleeve that fits snugly on the inner sleeve. The sleeve has now two layers.

Make sure that there is SUFFICIENT GAP between the two sleeves so that the core map can also be inserted into and can also slide in the GAP between the two front layers of the double layered slider.

Make the two layers stick together on their back sides by tapes or glue. Then cut the window through the outer layer so that the core map can be observed through the front window as if the slider sleeve was made of only a single layer.

Figure: The sleeve has two layers.

You may like to add the table of bright stars (Fig. 3) to the (uncut) back side of the double layered white sleeve to facilitate calling star names.

Choose the transparent sheet with the printed mask for your latitude. Cut it into a rectangular shape with 2 long arms extending from the East and West sides of the transparent grid mask. The rectangular transparent sheet has its width slightly wider than the width of the core map.

Insert the rectangular transparent sheet BETWEEN the two FRONT LAYERS of the double layered slider sleeve. Align the printed window of the transparent sheet to the cut window of the double layered sleeve. The East-West arms of the mask should be trimmed so that they only protrude slightly out of the double layered sleeve just enough to make easy insertion and removal of the mask.

In this way, any of the transparent mask can be fitted into or removed from the double layered sleeve whenever the user requires a new mask for his new latitude.

4. Final assemblage.

slideskymap15s

Figure 1: Front view of a Slide Sky-Map fitted with the mask for 15 degree South latitude.

slideskymap2backc100.jpg

Figure 2: Back view of a Slide Sky-Map.
Slip the core map into the inside of the double layered sleeve. The core map is now behind the transparent grid mask.

5. Usage.

The sky at night is represented by the core map going toward its west under the transparent window (that is it goes from left to right under the viewing window).

1/- Check that the center cross of the grid is on the declination line corresponding to your required latitude.

2/- The four vertical lines for equinoxes and solstices are printed on the core map. Other date lines are interpolated from them.

Place the center of the sliding window on the current date to see the mid-night sky for the date.

3/- Then slide the core map by half a division (15 degree on the equator or half a month) to the east or to the west for every hour ahead of or after midnight.

4/- The latitude for the grid not being exactly that of the observer and the true time at the location is not being equal to the zonal time causes the stars inside the smallest circle around the zenith to have slightly inaccurate position relative to the grid. However the lines joining these stars still give accurate directions and the stars still help identifying other stars near the horizon. The stars near the horizon have their values of azimuth and elevation angles given more accurately by the Slide Sky Map.

6. Record of a previous design.

(For reference only, do not use this obsolete design).

The slider consists of a white inner sleeve and a transparent outer sleeve tightly fit together.

Wrap a waterproof, white, thick sheet around the core (printed with maps) to make a white sleeve of no less than 360 degree along its East West direction (that is wrapping no less than two third of the length of the core map). The core should fit snugly inside the white sleeve and should be able to slide smoothly along its East West direction inside the white sleeve.

Cut a rectangular window on the front center of this white sleeve to reveal 180 degree width of the core map. You may like to add the table of bright stars (Fig. 3) to the (uncut) back side of the white sleeve to facilitate calling star names.

Choose the transparent sheet with the printed mask for your latitude. Cut it into the shape of a cross with 4 long arms extending from 4 sides of the transparent grid rectangle window. Each arm has its width equal to the size of the corresponding side of the adjoining window. Its North and South arms will be joined together to make a second, transparent sleeve fitting tightly outside the white sleeve, its long East and West arms will be slipped into the inside of the white, inner sleeve to anchor it on the white, inner sleeve. The East-West arms should protrude slightly out of the inner sleeve to make easy insertion of the sliding core into the white sleeve.

Wrap the transparent sheet tightly outside the inner sleeve and tape its North and South arms together to form a transparent sleeve with its grid right on the cut window of the inner sleeve. The East and West arms of the transparent sheet are slipped into the inside of the inner sleeve to lie along the East West direction underneath the white layer to anchor the transparent sheet on the white, inner sleeve.

In this way, any of the transparent outer sleeve can be fit into or removed from the inner sleeve whenever the user requires a new mask for his new latitude.

Slip the core map into the inside of the cardboard sleeve. Make sure that it goes behind the two transparent arms inside the sleeve so that it can travel fully from East to West.

Reference.

[1]. 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

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, posted on

Circumpolar Stars Nth

. Posted on May 25, 2016

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Slide Sky-Disks with grid masks showing azimuths and altitudes, posted on 03 Nov 2016 ,

, posted July 22, 2016DirectionTimeByStars

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Shadow stick navigation and graph of Solar paths

Shadow stick navigation and graph of Solar paths

by tonytran2015 (Melbourne, Australia).

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#find North, #finding North, #direction, #time, #shadow stick, #Sun shadow, #Solar declination, #graph, #Solar path,

Shadow stick navigation and graph of Solar paths.

In the 1950’s some maps have their graphs of Solar paths printed next to the compass roses. A graph of Solar paths helps the users of that map (for some certain small area) in orientating it correctly using only the direction of the Sun and the approximate time (month) in the year. It also help people visualize the direction of the Sun at each time of the year relative to a building. For some unknown reasons, graphs of Solar paths are all replaced by compass roses in modern maps. The roses take up nearly the same areas while give less information,.

A graph of Solar paths can also be used on its own with a vertical stick in the center to tell (local) time and direction. This application is suitable to day time navigation of vehicles as it relies only on the Sun and needs no battery. The application devices can be left on the vehicles as they are of very low-cost and are burglary resistant.

This posting shows how to construct and use a graph of Solar paths for your own map or for use on its own.

1. Description of the basic graph of Solar paths.

Solargraph10N

Figure: A typical graph of Solar path. This particular graph is made for 10 degrees North, for an example use in Saigon (around Tan Son Nhat International Airport).

The graph of Solar paths is a circular disc with concentric circles and radial lines bearing division marks to represent the elevation and azimuth angles of the Sun at different times of principal days.

The perimeter circle of the graph is graduated into 360 degrees to show the azimuth angle of the Sun from True North. It can also be used as a protractor for measuring angles. The concentric circles are the constant elevation circles.The radial lines are graduated 0 to 90 to show the angle from zenith to the Sun. The circle 90 degrees from the zenith represents the horizon in flat locations. The graduation can also be read from the horizon circle toward the center to show the elevation angle of the Sun.

All positions of the Sun at various time on an equinox day are plotted to make a Solar path for that day. The paths for the Sun on two solstice days are similarly plotted. The time for the each Solar position on a path is also given by time marks such as 6hr, 12hr and 18hr.

It is assumed here that the Sun attains its highest elevation at noon of local time everyday (the duration of the day is therefore slightly longer or shorter than 24hr, to discount any effect from the Equation of time).

2. Using a graph of Solar paths.

Be certain that the graph is for your current latitude! If it is printed on a map, it is for the latitude of that area.

The following steps show how to use the graph on an equinox day:

1/- Point your index to the Sun.

2/- Point your middle finger horizontally.

3/- Hold still the two fingers and measure the angle between them by placing those fingers along two radial lines of the Graph of Solar paths. Read the value of the angle. It is called the elevation angle of the Sun.

4/- Follow the Solar path for that day on the graph to its 2 points having that elevation value. The two intersection points give two times (one before and one after noon) and two positions of the Sun.

5/- Choose the one of those two points fitting your half day (either before or after noon-time).

6/- Lay the graph of Solar path horizontally. Rotate the graph until the line from the graph center to the chosen intersection point goes beneath the Sun.

7- The 0 degree azimuth line of the graph is now aligned along the direction of the true terrestrial North.

For any other day of the year, use the particular path for it. A graph supplies at least three paths: for summer solstice day (21 June for Northern Hemisphere), for equinox days (21 March and 23 September), and for winter solstice day (21 December for Northern Hemisphere). The path for any other day can be interpolated from these three.

3. Interpolation for any arbitrary day of the year.

wpid-divider10l.jpg

Figure: Solar declination for various days of the year.

The declination value for any day varies between the principal values for solstice and equinox days and its solar path varies similarly.

The rough graph here allows the estimation of how close the Solar path of any day is to its two neighbouring bounds for the equinox and solstice days.

4. Making a graph of Solar path for your latitude.

SunCelestSphere

Figure: The Celestial sphere directly above a circular disc of the same diameter.

The following steps show how to make your own graph of Solar paths for your arbitrarily chosen latitude.

1/-Draw 9 equidistant concentric circles and 12 (or 36) equally spaced radial lines as the frame for the planar polar coordinate system.

2/- Place this disc (as the frame) on a horizontal plane.

3/-Set the angle between 2 divider legs to be 90 degrees.

4/-Place the hinge of the divider exactly above the center of the disc. It should be at the center of the sphere in the figure.

5/- Hold the first leg of the divider pointing downward, inclined by latitude angle, in the 180 degree or 360 degree direction depending on your Lower Celestial pole being South or North Celestial pole. The first leg point downwards along the Celestial axis in the figure.

6/- The second leg will point at different directions to the Sun for different times of the day when the divider is rotated about the first leg. It uppermost position corresponds to mid-day.

7/- Looking downwards along the first leg of the divider gives the picture of a 24 hour clock with the second leg being the hour hand. The clock dial is clockwise when you are in Northern hemisphere and anticlockwise when Southern.

8a/- Looking at the second leg from the top of the disc gives azimuth angle of the Sun.

8b/- Looking at the second leg from its side gives elevation angle of the Sun.

9/- Record on the polar graph on the disc the direction of the second leg for 6hr, 12hr and 18hr.

10/- Join the curve by a smooth curve. (Additional points may be added for a more precise curve).

11/- The curve is the Solar path for equinox days.

12/- Set the angle between the divider legs to 90+23.5 degrees and repeat steps 4 to 10 to draw Solar path for summer solstice day.

13/- Set the angle between the divider legs to 90-23.5 degrees and repeat steps 4 to 10 to draw Solar path for winter solstice day.

The graph of Solar paths is now COMPLETE. It is usable with only 3 paths for equinox and solstice days. Paths for other days can be interpolated from them.

Manually drawn graphs are accurate enough for normal usage. If all steps are simulated with your computer, the graph will be very accurate.

If you live near to 20 degrees N latitude (20 degrees is only an example value) and need a graph for your personal use but don’t want to spend time drawing it, you can do a Google search for “graph solar path 20 degrees”. The search results will give many ready made graphs and you can select one of them for your own use.

5. Application 1: Shadow stick navigation for vehicles.

ShadowStick

Picture of Application 1: Shadow stick navigation for vehicles.

You can print your graph on a disc for use in your vehicle. You can use only one single disc if the vehicle does not travel more than 5 degrees = 300 nautical miles = 555km in latitude from your base.

Lay the rotatable disc horizontally with a vertical stick at its center. When the shadow of the stick is on the opposite side of the chosen point on the graph, the line of 0 degree points exactly at True North. This method of Solar navigation only needs the graph and a vertical stick and is immune to vehicle shocks and stray magnetism.

This method needs the above device and is less general than my other methods given in references [1, 2, 3] but may be easier for users to comprehend.

6. Application 2: As a North direction marker

DirectionMarker

Picture of Application 2: As a North direction marker

Figure: Map of an old citadel overlaid on a modern satellite based map. The graph of Solar paths is given on bottom left corner instead of the compass rose.

The illustration is the map of an old citadel overlaid on a modern satellite based map. The graph of Solar paths is given on bottom left corner instead of the compass rose. The graph of Solar paths gives more useful information than a compass rose occupying same area.

Notes on my composite map: The modern map data are used under Open License from Open Street Map, the data are owned by Open Street Map Contributors. The old area has adjusted and selected data from a 150 year old map with expired Copyright.

7. Additional observations.

The graph of step 1 shows that the Sun can travel on the other side of your zenith when you are in a tropical zone. This explains why the bisector method using a horizontal watch may give you an error of 180 degrees around summer solstice (see reference [2]).

The graph shows that the terrestrial direction (azimuth) angle of the Sun varies quickly with time when the Sun is close to the zenith point. This quick change in direction may be main the reason for the ancient custom of cross-country travelers to take their rest when the Sun is near to their zenith.

You can also use a graph for your EXACT latitude to calculate if and for how long a proposed neighbouring tall building may over-shadow your house. Architects have been using graph of Solar paths and physical sunlight simulator on their scale models even before 1914.

References.

[1]. 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.

find North by the Sun

[2]. 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

[3]. tonytran2015, Caution in finding North by bisector line of a horizontal watch, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/10/28/caution-in-finding-north-by-bisector-line-of-a-horizontal-watch/, Posted on October 28, 2015.

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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.

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Selecting and using magnetic compasses.

Selecting and using magnetic compasses

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, #select, #use, #operate, #North, #magnetic.

Selecting and using magnetic compasses.

A magnetic compass uses the local magnetic field generated by the rotating core of the earth to give the rotational axis of the earth. The two directions are reasonably close.

The magnetic compass is a secondary directional instrument to people who can observe celestial bodies for navigation but is a primary practical directional instrument to people who cannot observe any Celestial body. (Gyro-compasses are too expensive for most people).

Here is the list of desirable features for selecting a compass and different usage modes of magnetic compasses.

A compass should have at least the following desirable features:

1. Robustness,

2. Durability,

3. Wide operational conditions (being stable despite harsh operating conditions),

4. Accuracy (being true and sensitive),

5. Simplicity,

6. Portability, and

7. Versatility.

1. Robustness.

Magntic Compasse

Figure 1:(Left to right) Tiny liquid filled disc compass, simple compasses with and without needle lock.

Compass Meridional fake

Figure 2: A HAZARDOUS Chinese imitation of the German Kasper & Richter Meridian sighting compass, the imitation has its graduation markings self-detached after only washing by clean water from a tap! The black markings on the white rotating dial under the top circular glass can be seen lying randomly after peeling off.

A serious compass should be able to withstand falls of 2m into boxes of sands, to withstand hot and cold environmental temperatures, to withstand immersion in water, to withstand strong sunlight.

The liquid inside a liquid filled compass reduces stresses on the pivot caused by linear acceleration on the mass of the compass needle assembly; this makes the compass more robust. Serious dry compasses should have needle locks to remove acceleration stresses on pivots.

Liquid filled compasses should have pivots with spherical heads. These spherical heads need to be covered by lubrication fluid in operation but last longer than those with pointed conical head.

The Chinese, tiny (originally liquid filled) compass of Figure 1 has completely dried up after about one year of usage. However, it can still correctly point North when given gentle vertical vibration during use.

Figure 2 shows a hazardous Chinese imitation of the German Kasper & Richter Meridian sighting compass, the imitation has its graduation markings self-detached after only washing by clean water from a tap! The black markings on the white rotating dial under the top circular glass can be seen lying randomly after peeling off. (The blue line markings are mine to show what were there). This may lead to a SERIOUS situation to its inexperienced user while in the field. This type of products should be banned in Western countries.

2. Durability.

Compass Magnetic

Figure: An old ex-US Army lockable dry compass (made around 1965, initially known as M-1950 compass) from disposal stores remains robust and can keep on working although the clear glass has become partially clouded.

Any serious and expensive compass should withstand the passage of time (being durable).

Some types of PVC materials disintegrate with time. Some clear plastic may become cloudy with time. Some liquid filled compasses leak and dry up with time. The needle points of some dry compass may rust away with time.

3. Wide environmental tolerance in many modes.

Compass Lensatic Chinese

Figure: A Chinese lensatic compass with unreadable direction graduation due to wrong focal length of its lens. The round sighting lens has to be disassembled and reground and it is placed on the clear dial near to the 260 degree position of its rotating compass rose. ===>> All functioning parts of any compass must be tested before taking it to the field!

A compass should function even in non-level position or with highly inclined magnetic field, with unsteady hand holding, in cold or hot temperature, at normal or high altitude, when submerged in water, during the day or at night.

It should be able to function in its different operation modes.

Conical cup bearing on needles are more tilt tolerant. Low center of gravity of a needle allows the compass needle to resist the vertical tilt of any highly inclined magnetic field. Liquid filled compasses with non-flexible liquid capsules need to have allowance for non-interfering bubble or have undulating flexible bottom to allow volume change of the fluid. Temperature extremes and external atmospheric pressure can change the volume of the fluid and make liquid filled compasses leak. Any air bubble in its liquid capsule will reduce the till tolerance of a liquid damped compass. A capsule with air bubbles inside will cave in under external pressure and may crack when used for diving.

Mirror compasses also allow magnetic readings free from users’ own magnetic field.

Testing for tilt tolerance:

Tilt the compass in various directions until contact friction affects the reading. Work out the angle of tilt that still allow smooth operation of the needle. Work out the pitching of the needle due to the pitching of magnetic field. Check if this pitching can cause contact friction between the needle or compass rose plate and the case.

Night vision:
Night vision can be provided with either phosphorescent paint or radiation illumination. Phosphorescence requires energizing by a torch for few seconds every hour. Radiation is only acceptably safe if it is from Tritium.

4. Accuracy.

Compass Lensatic

Figure 1: Horizontal rotation test to detect resolution and cogging.

Compass Jap. Lensatic2

Figure 2: Japanese compass with agate jewel. The bearing on its rotating disc has an agate center, in contrast to the Chinese compass of Figure 1 with all metal bearing (no jewel).

Figure 3: Japanese compass with agate jewel. The bearing on its rotating disc has an agate center, in contrast to the Chinese compass of Figure 1 with all metal bearing (no jewel).

a. The compass should correctly show the magnetic North. (I have seen some cheap liquid damped compasses with the needles glued to the disks with enormous errors of about 20 degrees from their intended positions!)

b. The readings should then increase or decrease by values equal that caused by the horizontal rotation of the aiming line. This is required for interchangeability of data.

Accuracy test.

– Draw two pencil lines intersecting at right angle in the center on a piece of paper.

– Place the paper on a flat table face with one of the line accurately aligned along the magnetic field.

– Place the compass at the intersection at the center of the paper and read the direction of the needle relative to the pencil line.

– Smoothly rotate the compass case in one direction about the needle pivot to discover any cogging caused by any inappropriate use of magnetic material in the case. The induced eddy current in the non-magnetic material is too weak to cause any cogging. An accurate compass should not have any cogging.

– Smoothly rotate the compass case in the other direction about the needle pivot to discover any cogging caused by any inappropriate use of magnetic material in the case.

– Let one pointed magnetic pole of a long magnet comes gradually close to the compass along a spiraling path and check if one of two ends of the compass needle points exactly at it.

Without accuracy, your compass may send you astray by up to 20 degrees !

Accuracy test is a difficult one. It requires a uniform magnetic field with known orientation and strength. The magnetic needle of the compass should be symmetrically manufactured and magnetized. We must first eliminate compasses with obvious manufacturing defects on needle (being non-symmetric, badly mounted to the rotating needle disk). Accuracy requires:

1/- The dial must be circular and evenly graduated.

2/- The pivot of the needle must be exactly at the center of the circular dial and the pivot to be at right angle to the dial surface for the reading to be correct.

3- The magnetic needle must be metalurgically symmetric with respect to its center line.

With all different orientation of an accurate compass the two ends of the magnetic needle point to readings with difference of 180 degrees all the time. Even if a magnetic needle looks externally symmetric, its material properties may not be uniform. The metallurgical and mechanical history of a piece of material will definitely affect its magnetic properties. Only sprinkled iron powder can reveal the magnetic field of a compass needle. For this reason users have to stay away from cheap compasses with needles made from steel off-cuts and scrap materials as the needles may not be able to be magnetized to bear symmetric magnetic field.

If your compass is accurate it should give the accurate magnetic declination figure for your area from Sunrise and Sunset directions or from True North given by your street maps. The yearly figures for magnetic declination can be found from the internet for comparison.

Some quality compasses can provide accuracy of up to one degree. This gives accurate identification of destination and reduces unnecessary turnings. Accurate direction is vital when calling for base support.

Resolution test:

This test finds out how much change in direction can remain undetected by your compass.
1/- Find a level, steady surface, away from any magnetic source to place the compass .

2/- Set the compass sight on some easily seen object.

3/- Rotate compass anti-clockwise by about 90 degrees. Slowly and gently rotate the compass back into sighting position aiming at the same object. Write down the first reading for bearing.

4/- Rotate compass clockwise by about 90 degrees. Slowly and gently rotate the compass back into sighting position aiming at the same object. Write down the second reading for bearing.

5/- The two readings should differ by no more than 2 graduation units.

The difference is called the resolution of the instrument. A respectable instrument maker would not give a finer scale than the instrument can ever resolve! If the resolution is less than half a unit, the reading is meaningful to the last graduation unit.

The Japanese lensatic compass in figures 2 & 3 has jewel bearing at the center of the compass needle to reduce rotational friction. This is clearly shown in contrast to the cheap Chinese compass of figure 1.

5. Versatility.

Compass Mirror Hong Kong

Figure: Simple compass made of steel needle, clear plastic capsule, glass mirror and flexible case. This compass is not liquid damped, has no jewel bearing, and its mirror has no see through hole for aiming. It is NOT a serious compass !

Figure: A low cost 75mmL X 40mmW plastic mirror-compass with thermometer and relative hygrometer on its top cover. The inside of the top cover has a bright 75mm X 40mm metal mirror.

Extra features like mirror, lenses may help with grooming, fire making, observation, signaling.

Figure 3 of Step 1 shows a design with a bull eye for leveling and a vertical scale. Vertical graduation and accurate leveling of base allow determination of elevation.

The sighting mirror of the mirror compass in figures 1 and 2 of step 8 can also be used as a signaling mirror and personal mirror. This feature was favoured in the 1940’s.

Being waterproof and unsinkable
This is a requirement for adventurers, hikers and fishermen. If the compass is waterproof and light, it can float in water. A number of liquid filled compasses with plastic cases are light and can be made unsinkable if glued to some thick sheets of light styrene foam.

6. Simplicity.

Sighting Compass Imitation

Figure 1: A simple, plastic compass based on the Suunto compasses for touring. Please note that this imitation compass may be neither as durable nor as reliable as the genuine one.

 Sighting Compass Imitation 2

Figure 2: A simple, plastic compass based on the Suunto compasses for touring. Please note that this imitation compass may be neither as durable nor as reliable as the genuine one.

Sighting Compass Imitation

Figure 3: A simple, plastic compass based on the Suunto compasses for touring. Please note that this imitation compass may be neither as durable nor as reliable as the genuine one.

Figure 4: A high quality Suunto compasses for marine, professional and outdoor use (Image added after 2018 May 07).

A well made, simple compass rarely has malfunction and the first sign of any malfunction is obvious to see.

Liquid filled compasses will show bubbles when any liquid is lost and the malfunction and loss of robustness are gradual.

7. Portability.

A compass should be light and small enough to be carried around.

Robust but cumbersome or heavy compasses make users unnecessarily tired, I would not carry them. They are only good for laboratories or surveying teams.

If a compass has a holding ring or carrying string/strap, I would tie a string to that and pull the ring/string/strap with 10 times the weight of the compass to test its strength (10g acceleration endurance) before use, to prevent loss of the compass during field use.

8. Find North by a Compass: Magnetic and True Norths.

Magnetic Declination

Figure: True North, Magnetic North and Magnetic Deviation.

Obtain the magnetic deviation for your area. This deviation is commonly between (-45) degrees and +45 degrees and it slowly changes to a new value every year. The deviation is obtainable from the internet or by the method given in reference [2]. Positive magnetic declination means the Magnetic North is on the East of True North.

If you have a really erasable marker for your top glass/plastic dial, you can use it to mark the magnetic deviation from the long marking line for True North on your compass dial. The marking has to be erased and redone when the deviation has changed significantly. If you don’t want to mark on the dial, you can stick a tape on the underside of the compass and write clearly on it something like “MD = (-1)deg” (This is only an example value, your value is different).

Every time you use the compass, you only need to align the needle/rose to your marking on the dial and the long line for True North on your compass is already aligned.

If you do sighting using a compass with a rotating compass rose which always points to magnetic North, just read the graduation on the card and ADD the signed magnetic declination to it.

9. Precaution against magnetic anomalies.

Find North by watch

Figure: Cross checking directions with those from a Celestial method whenever possible is a desirable habit. This illustration is from reference [7].

Find North by the Sun and a divider

Figure: Cross checking directions with those from a Celestial method whenever possible is a desirable habit. This illustration is from reference [4].

Besides magnetic deviation caused by the core of the earth, there are also deviations near ground surface caused by man-made objects and ore bodies. These are called “Magnetic Anomalies”. An anomaly produces non-parallel magnetic field lines and non-constant magnetic field strength.

The following steps help to detect any magnetic non-uniformity in order to detect such anomalies and to avoid disorientation when using a magnetic compass (A magneto-meter is better for this detection as it supplies the extra accurate value of field strength but it requires batteries.).

1/- Count the yaw and pitch oscillation frequencies of the needle of any new compass. Write them on a piece of paper for future reference.

2/- Check the polarity and the yaw and pitch frequencies before packing the compass for any trip. If the frequencies have decreased the needle may have lost part of its magnetism and re-magnetization may be needed.

3/- Have a habit of cross checking directions with those from Celestial methods (given in references [4,5,6,7]) whenever the Sun or the Moon or bright stars can be seen. The cross checking with the direction determined by the method given in [7] also verifies that your watch is still working.

4/- Frequently take the bearing of your destination in both standing and crouching/sitting positions (with different heights), even if you are confident of your current position. This ensures that your compass is ready when needed and you are prepared against any sudden loss of visibility (due to change in weather, terrain, falling down a crevice! . . .). Any quick change in magnetic direction with height or with horizontal travel distance usually reveals a very strong, meter-scaled magnetic anomaly. The anomalies may be caused by buried metal objects (steel-reinforced bunkers, car bodies, tank bodies, unexploded bomb-shells!, magnetic ores,…) or even induced magnetic field from high voltage power lines.

5/- If anomaly is suspected, count the yawing frequency of the needle. The external field strength acting on the needle is proportional to the square of this frequency. For example, if the frequency goes up by 2, the external magnetic field strength may have gone up by 4.

6/- Distant objects such as mountain peaks, light houses, transmission towers can help detecting the sudden change in magnetic deviation when you travel. The magnetic bearings of these distant objects should only change slowly. If there is any sudden change in their bearings you may have to check the accuracy of your compass or the change in magnetic deviation.

Note:

Compasses are usually NOT suitable for rail travelers as the carriage bodies and the rails underneath it creates magnetic abnormality.

10. A special mode of operation to reduce own influence.

Compass mirror Chinese

Figure 1: Plan view of a plastic mirror compass. The mirror is opened by 110 degrees from its close position.

Compass mirror Hong Kong

Figure 2: End (operational) view of the same mirror compass. The mirror is opened by 45 degrees from its close position. The clear capsule should be rotated by the thumb until the fluorescent double II marking on it is on top of the North end of the needle. The compass should be hold in the air by the hand of a stretched arm.

Using the Mirror Sighting compasses.
The Mirror Sighting compasses are for a special mode of operation with reduced influence from user’s magnetic field. This feature allows the compass to be used with stretched arms keeping it away from the user’s body. A mirror compass is used in the following way:

Hold the mirror compass at your eye level, horizontally level on one stretched arm, away from your head, with the mirror tilted from the vertical by 45 degrees to let your eyes see the reflection of the working horizontal needle and dial of the compass. Take aim of the destination by the aiming guide and observe the horizontal magnetic needle through the mirror. Rotate the rotating dial on top of the needle to mark the position of the needle. For accuracy, keep the vertical marking line on the mirror superimposed on the aiming diameter of the horizontal dial of the compass. Finally bring the compass to your comfortable reading distance to read the marked position of the needle. The magnetic bearing of the aiming line is the value on the scale at the point nearest to the mirror.

This is a desirable feature if the user carries magnetic items and it is not practical for him to take off these items when using the compass. The sighting mirror can also be used as a signaling mirror and personal mirror. This feature was favoured in the 1940’s.

The compass in figure 2 has only a very crude aiming guide. It follows the design of Silva Trekker compasses.

Using the lockable compasses.

Compass M1950 away from body

Figure 3: Hand posture for holding type M-1950 compass for sighting with a stretched arm. The finger through the brass ring is the middle finger. The sighting is carried out using the slit in the sighting tab and the wire in the lid. The lens has no function in this sighting mode. This is my own novel mode of operation not designed by the makers of type M-1950 compasses.

Any tilt tolerant, lockable compass can also be used in this mode (with reduced accuracy) even without any mirror. Tilt tolerance ensures that the needle can point North before the lock is engaged to freeze it in place. The ex_US Army compass (model M-1950) in figure 1 of Step 2 can be used in this mode, and is surprisingly accurate, as it is tilt tolerant and the inertia of its rotating compass rose ensures that the needle orientation is retained while the lock is engaging. A lockable M-1950 compass is used in the following way (This is my own novel mode of operation, not designed by the makers of type M-1950 compasses. Do NOT complain to them that their compasses are not comfortable to use in this way!) :

Place the lid and the sighting tab of the M-1950 compass in vertical positions to have the compass in unlocked and operating condition. Turn the holding ring near the sighting tab fully downward. Curl the middle finger of your hand and stick it through the holding ring of the compass. Grip the compass by pressing the end of the index finger against the lid hinge and the joint of the thumb against the sighting hinge. Stretch your arm while holding the lensatic compass horizontally level at the height of our eyes, away from your head, with its lid vertical and its lock still fully disengaged (sighting tab in vertical position).

Take aim of the destination by the aiming guide then hold till for 3 seconds. Gently engage the lock (push the sighting tab into horizontal position) by only raising only the first joint of your thumb to push against the bend of the sighting tab while keeping the rest of the body motionless. After having been locked, the whole compass is bought to your comfortable reading distance to read the locked position of the needle. The magnetic bearing of the aiming line is the value on the compass rose at the point nearest to the hinge. It is hard to read but is definitely readable even with the sighting tab fully down.

11. Special Operating mode 2: Using small, fluid deficient compasses.

Compass Tiny 1

Figure 1: A two years old Chinese key-ring compass (with diameter of about 20mm) has visible air bubbles. Some bubbles or all bubbles may stick under the compass disc, under the S.

Compass Tiny 2

Figure 2: A two years old Chinese key-ring compass (with diameter of about 20mm) has visible air bubbles. Some bubbles or all bubbles may stick under the compass disc, under the SW.

Compass tiny 3

Figure 3: The compass is tilted by 100 degrees to have all bubbles collected at the upper side of the compass disc.

Compass Tiny 4

Figure 4: All gas/air is now above the compass disc.

A fluid deficient liquid filled compass should be repaired and refilled with the same type of fluid to restore its original, designed performance. However, a small such compass can still be used in reduced performance mode (for emergency) employing the following work around.

The capsule of of the liquid filled compass should be held upright. It is then tilted 100 degrees from its upright position to let any bubbles from underneath its compass rose (rotating disk) escape to the space at the top of the (now vertical) rim of the rose. The capsule is then tilted back to its upright position, ensuring that all air stays above the rotating rose. With all air expelled to the top of the compass rose, the latter can rotate although with reduction in accuracy because of undue tilting torque exerted by air bubbles.

Gentle tapping and vibration in the direction of the pivot axis will free the rose in multiple short time intervals while it travels/bounces between extreme positions. This is sufficient to make the magnetic needle of the rose point close to magnetic North.

Any small, completely dried, liquid filled compass may be made pointing North by such gentle vibration/rattling.

The method in this section may not be applicable to large marine compasses without Cardan gimbal mounts!

12. Special Operating mode 3: Using compasses balanced for the other hemisphere.

The magnetic field generated by the interior of the Earth looks like that of a giant dipole magnet placed at the center of the Earth and of length equal to the radius of the Earth. At the equator the field is parallel to ground surface while it goes into the ground away from the equator.

On the Northern hemisphere the North end of a compass needle is pulled towards the ground while on the Southern hemisphere the corresponding South end is.

This may make the ends of a symmetric compass needle in a thin circular compass touch the upper or lower part of the case, causing dragging friction.

The problem has two simple solutions for compass makers. Firstly the center of gravity of the needle should be made much lower than the tip of the pivot. Secondly, one needle end can be made heavier than the other to resist the pitching caused by the inclination of the magnetic field.

Most compass buyers live in Northern hemisphere so compass makers tend to make their products work from the equator to about 60 degrees Northern latitude. They just simply make the South ends of their compass needles heavier than the North ends. The so made compasses are said BALANCED for Northern hemisphere. You can notice that the North ends of their needles mostly rise up when used near the equator.

When these compasses are brought to the Southern hemisphere the South ends of their needles are pulled even further down, resulting in dragging.

A user on the Southern hemisphere may have to hold his compass case at angle to avoid dragging or to RE-BALANCE the needle by wrapping some copper wire around the Northern half of the compass needle.

Re-balancing requires delicate work on the compass and requires opening it every time you move to the other hemisphere. Here I offer a very effective and simple method of using the same compass in both hemispheres.

My solution is to magnetize the light end of the needle to be a North pole when in the Northern hemisphere and a South pole when in the Southern hemisphere. (The colour on the needle should now only mean a light or a heavy end.)

The method and the simple tools to re-magnetize a steel compass needle has been described in a previous Instructables posting, reference [1].

A compass with non-steel needle cannot be re-magnetized by this method.

Please leave any comments and suggestions here so that the posting can be improved !!

References.

[1]. tonytran2015, Beware of perilous flips by magnetic compasses, survivaltricks.wordpress.com, , posted on June 14, 2016.

[2]. tonytran2015, Determining local magnetic declination by a magnetic compass, survivaltricks.wordpress.com , Determining local magnetic declination by a magnetic compass, posted on March 31, 2016.

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

[5]. tonytran2015, Finding North direction and time using the hidden Sun via the Moon, survivaltricks.wordpress.com, Finding North direction and time using the hidden Sun via the Moon . Posted on July 6, 2015.

[6]. tonytran2015, Finding North direction and time by stars, survivaltricks.wordpress.com, Finding North and time by stars. Posted on August 28, 2015

[7]. tonytran2015, Finding accurate directions using a watch, posted on May 19, 2015 .

DirectionBySun_12N

NorthByWatch2

Added after 2018 Feb 19:

[8]. “The compass was first used in India, around 1800 BC, for Navigational purposes and was known as “Matsya yantra” (which roughly translates to fish machine) because of the placement of a metallic fish in a cup of oil. The use of the magnetic compass started from 4th century in china, where a type of magnetite known as “lodestone” was used as a tool in a kind of divining magic, Geomancy. The Chinese were the first ones to have mastered the use of magnetic iron for navigation, which then rapidly spread to Europe and beyond.”, .https://knowledge4civil.wordpress.com/2017/07/23/types-and-uses-of-compass/

[9]. https://misfitsandheroes.wordpress.com/2018/01/15/fat-boys-magnetism-and-magic/

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