Adding Longitude and Latitude Lines to a map

Adding Longitude and Latitude Lines to a map

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.78).

#find North, #GPS, #navigation, #off grid, #adding, #longitude, #latitude, #coordinate, #lines, #map,

Adding Longitude and Latitude Lines to a map.

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 or when going hiking.

If you want to use your GPS off-grid with any map, you need to draw on top of the map an accurate system of regularly spaced longitude and latitude coordinate lines.

This posting shows how to add the lines.

1. 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…

2. Make sure that the top of the map points to true North. (In some countries, maps are deliberately oriented at angle to true North, probably for security reasons.)

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.

3. 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 two to four such fearures located near the four extreme corners of your map. They will be used as land marks.

Ecample:

The 3 landmarks that can be used 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

4. 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 land marks.

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

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

6a, If the map and grid are both digital, they can be superimposed in the computer to produce the following map with added coordinate lines:

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.

The added lines are on round figure coordinates and are 2 minutes of arc apart. The intersection nearest to the NW of Tullamarine airport has coordinate (144°50′E, 37°40′S ).

6b. If you are using printed map: Join two distant landmarks on the coordinate sheet and notice where the lines of “minute of longititude” and of “minute of latitude” intersect it

7. If you are using printed map: Reproduce that line, with all its intersecting points, on the actual paper map.

8. If you are using printed map: From these intersecting points project corresponding vertical lines to make the “minute of longititude” lines and horizontal lines to make “minute of latitude” lines.

9. The map is now graduated with longitude and laritude lines.

10. Its grid can now be used as a base to draw finer grids for detail maps with higher resolutions.

2. Using GPS with maps.

You can download a (preferably 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.

It is preferable 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.

References

[1]. tonytran2015, Using GPS in off-grid situations., posted December 6, 2016

[2]. 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.

[3]. 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.

[4]. , BBC News, UK radio disturbance caused by satellite network bug, http://www.bbc.com/news/technology-35463347, 2 February 2016.

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

PREVIOUS SURVIVAL blogs

, posted on

Circumpolar Stars Nth

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

Compass-Magnetic

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

Slide Sky-Map for displaying tropical stars.

Click here for my other blogs on divider43.jpgSURVIVAL

Click here go to Divider63D400 Home Page (Navigation-Survival-How To-Money).

SUBSCRIPTION: [RSS – Posts], [RSS – Comments]

MENU: [Contents][Blog Image of Contents ][Archives ] [About]

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

RELEVANT SURVIVAL blogs

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

Compass-Magnetic

, posted on ,

Circumpolar Stars Nth

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

Find North by Shadow Stick

Using GPS in off-grid situations., posted December 6, 2016

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

map with longitudes n latitudes

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

radio sony

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

find North by moss

PREVIOUS SURVIVAL blogs

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

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

Identifying moderately bright navigational stars.

Slide Sky-Map for displaying tropical stars.

Click here for my other blogs on divider43.jpgSURVIVAL

Click here go to Divider63D400 Home Page (Navigation-Survival-How To-Money).

SUBSCRIPTION: [RSS – Posts], [RSS – Comments]

MENU: [Contents][Blog Image of Contents ][Archives ] [About]

Finding direction, distance and navigating to a distant base by stars, fine reading of latitude (Part 2).

Finding direction, distance and navigating to a distant base by stars, fine reading of latitude (Part 2)

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, #star, #sky map, #sky disk, #declination, #right ascension, #fine reading, #celestial, #distance, #find, #latitude, #navigation, #no instrument, #polynesian, #zenith,
This is applicable to navigation in an ocean or in a large desert with clear, flat horizontal skyline. It uses the complementary stars touching the horizon instead of stars traveling directly over the zenith of the navigator. It is more suitable for sea travel with readily available horizon but unsteady travel platform. It is a useful trick to return to a base (e.g. a Polynesian island) when having no measuring instrument.

Step 1: Basis of the method.

BStarsN20Vega8C

wpid-30naugplrnc-.jpg.jpeg

wpid-30naugplrsc.jpg

Figure: The trajectory of the complementary star touches or nearly touches the horizon. Figures: Horizon for an example latitude of 30degrees North projected onto North and South Celestial hemispheres respectively.

Stars travel along constant declination circles drawn on the Celestial sphere. If the base city is at latitude L then the constant declination circle of 90°-L on its same (North or South) hemisphere will be seen touching the horizon and the lowest position of the complementary star will be right on the horizon and in the principal Northern/Southern direction. When the (complementary) stars of declination 90°-L is at its lowest point near the horizon, unaided human eyes can easily tell its elevation accurate to 1/4 Moon’s diameter (1/8 of a degree).

If bright complementary stars are unavailable for any latitude, users of this method have to identify some constellations having dim complementary stars for that latitude and use these stars instead.

Step 2: Preparation at base for this method.

BrightStars0b

polrnorthqrefc60.jpg

polrsouthq3c60.jpg

Figures: 20 brightest stars and their positions in the sky represented in Northern and Southern 3/4 spheres. Dimmer stars beyond this list may have to be used by this method for traveling to any arbitrarily given latitude.

1. Work out the latitude of the chosen city.
2. Work out the complementary angle for that latitude.
3. Use a list of bright stars (in reverse order of brightness) to choose a star or stars having declinations being equal or greater than the complementary angle by less than 2 degrees (the difference is less than 2degrees or 4 Moon’s diameters). The less bright stars may have their declinations closer to required values but their poor visibility may make them unsuitable. The chosen star may slightly dive under the horizon but its neighbouring stars can indicate how far it has dived.
4. Practice identifying the complementary stars in all imaginable conditions.

Step 3: Field application

5. Travel North or South until the lowest position of the complementary star touching or slightly above the horizon by the so determined adjustment of less than 4 diameters of the Moon.
6. On attaining that latitude, only travel along a parallel circle to maintain the latitude.

Step 4: Examples.

BStarsN20Vega8C2.jpg

Figure: The trajectory of the complementary star for London touches or nearly touches the horizon when viewed at the latitude of London.

London is at (0°5′ longitude, 51°32′ latitude), choose Vega (18hr 37 RA, +38.8deg declination). Around midnight of Dec. 25th, the star Vega travels to its lowest point on a circle glancing the horizon. Its distance from horizon is 51°32 + 38.8° – 90° = 0.3°.
This angle is half the diameter of the Moon and can be judged accurately by unaided eyes.

Berlin is at (13°25′ longitude, 52°30 latitude), choose Vega (18hr 37 RA, +38.8deg declination). Around midnight of Dec. 25th, the star Vega travels to its lowest point on a circle glancing the horizon. Its distance from horizon is 52°32 + 38.8° – 90° = 1.3°.
This angle is 3 diameters of the Moon and can be judged accurately by unaided eyes.
Manila (120°57′ longitude, 14°35′ latitude), choose a dim star Beta Ursae Minoris, (Kochab, 14hr51RA, +74.3deg declination). Around midnight of Nov. 07th, the star Kochab travels to its lowest point on a circle glancing the horizon. Its distance from horizon is 14°35 + 74.21° – 90° = -1.3° (under the horizon by 1.3degrees. This angle is 3 diameters of the Moon and cannot be seen but its visible neighbouring stars in the Ursa Minoris group can indicate how far this star is below the horizon.).
Mecca(39°45 longitude, 21°29 latitude) choose Gamma Ursae Minoris (Pherkad Major, 15hr 21RA, +71.8° declination). Around midnight of Nov. 16th, the star Kochab travels to its lowest point on a circle glancing the horizon. Its distance from horizon is 21°29 + 71.8° – 90° = +3.3°. This angle is 7 diameters of the Moon and can be judged accurately by unaided eyes using fingerwidths on a stretched arm.

Tonga Capital city is Nukuʻalofa (175°12′W = 184°48′ longitude, 21°08′S latitude). Choose the star Beta Carinae (Miaplacidus 09hr 13 RA -69.7decl). Navigators may have to identify the constellation Carina containing the bright star Canopus in order to identify a not quite bright Beta Carinae. Around midnight of Aug. 10th, the star Beta Carinae travels to its lowest point on a circle glancing the horizon. Its distance from horizon is 21°08′ + 69.7° – 90° = +0.8°. This angle is 1 and 1/2 diameters of the Moon and can be judged accurately by unaided eyes.

The Northern tip of Iceland is at 66°30′ (see the map from viking ships , [2]). Choose the Sun at its June 21st solstice. Around midnight of Jun. 21st, the center of the Sun travels to its lowest point on a circle glancing the horizon. Its center is exactly on the horizon when the navigator is on the latitude of the Northern tip of Iceland. The upper rim of the Sun is just touching the horizon on Jun. 21st when the navigator is on the latitude of Northern Iceland. Keeping this latitude brings the navigator to Iceland on a journey of 900km from Norway.

Step 5: Notes on terminal homing of journeys.

Near to the end of his journey, an ocean navigator may release island spotting birds.
If the birds can attain a height of 800m, they can spot land (even without using cloud features) at distance of 110km away (60 nautical miles, or 1 degree of arc or 2 Moon’s diameters).
If the birds can attain a height of 250m, they can spot land (even without using cloud features) at distance of 55km away (30 nautical miles, or 0.5 degree of arc or 1 Moon’s diameter).
If the birds can attain a height of 62m, they can spot land (even without using cloud features) at distance of 28km away (15 nautical miles, or 0.25 degree of arc or 0.5 Moon’s diameter).

Alternatively the navigator may note the presence of nautical birds from the island ( viking ships , [2]). The navigator can also use currents, winds and even smells in this phase.
The error of this navigation method is thus well within the operational range provided by the spotting birds.

References

[1]. tonytran2015, Finding direction, distance and navigating to a distant base by stars (Part 1). Additional Survival tricks, wordpress.com,
Posted on January 27, 2016.

[2]. viking ships , http://www.hurstwic.org, http://www.hurstwic.org/history/articles/manufacturing/text/norse_ships.htm

Added after 2018 July 20:

[3]. https://misfitsandheroes.wordpress.com/2012/08/28/ancient-navigators/

RELATED SURVIVAL blogs

, posted on

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

Sky map Northern 3/4 sphere

Sky map Southern 3/4 sphere

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

image

image

, posted July 22, 2016

DirectionTimeByStars

 

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


Click here for my other blogs on divider43.jpgSURVIVAL

Click here go to Divider63D400 Home Page (Navigation-Survival-How To-Money).

SUBSCRIPTION: [RSS – Posts], [RSS – Comments]

MENU: [Contents][Blog Image of Contents ][Archives ] [About]

Finding direction, distance and navigating to a distant base by stars (Part 1)

Finding direction, distance and navigating to a distant base by stars (Part 1)

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, #star, #sky map, #sky disk, #declination, #right ascension, #celestial, #distance, #find, #latitude, #navigation, #no instrument, #polynesian, #zenith

polrnorthqrefc60.jpg

Figure: The sky map for use in Northern hemisphere.

The method here uses stars for finding base city at a distance between 1000km to 9000km and for traveling to that base using constant latitude for final path.
It uses the stars passing overhead the base city and accurate time to tell those moments. Direction and distance to that city are directly observed from the stars. If no current longitudinal information is available and longer travel distance is acceptable then the user can also use this method to aim for base city on the final constant latitude part of the travel.
This is a back up or emergency method for people who may need to find out their direction to base and how to arrive there even when having no landmarks for current position. This is the case for:
A. People who are lost in the ocean or in a large desert with no reliable landmark. They need some method of orientation using minimal number of tools.
B. People drifted to an isolated island in the ocean after a tsunami !
C. Installers of long distance or satellite communication antennas wishing to aim their devices when not having any map.
Required information:
1. Selected star(s) for the chosen base city with the target point(s) underneath the star(s) reasonably close to the base city.
2. Longitude of the base city and time signal announcing GMT time to show the time at base city. The time signal may come from Broadcast or Marine Band Weather Radio.
3. or an accurate watch that allows determination of the true (not zonal) time of base city (Each minute earlier or later than intended time may cause a longitudinal error of 0.25 degree that is about 27km near the equator.).

Step 1: Preparation before expedition

polrsouthq3c60.jpg

Figure: The sky map for use in Southern hemisphere.
1. Search from the list of brightest stars (in descending order) for the brightest identifiable star that can closely pass overhead the base city (with acceptable error distance) and the approximate date for it to be seen in at midnight.
Examples:
London is at (0°5′ longitude, 51°32′ latitude). In June, choose Eltanin (Gamma Draconis, 17hr 57′, +51.5° declination) target point underneath the star is 0km from base.
Berlin is at (13°25′ longitude, 52°30 latitude). In June, choose Eltanin (Gamma Draconis, 17hr 57′, +51.5°declination), target point underneath the star is nearly 110km South of the city while the zenith of the city is 2 Moon’s diameter from the star and toward the Celestial North . In December choose Gamma Persei (03hr05RA +53.5degrees declination, app magn 2.91) target point underneath the star is nearly 110km North of the city while the zenith of the city is 2 Moon’s diameter from the star and toward the Celestial South.
Mecca(39°45 longitude, 21°29 latitude) choose ArcturusBoote (213.9RA, 19.2° declination) nearby location underneath the star is 230km South of the city while the zenith of the city is 4 Moon’s diameter from the star and toward the Celestial North.
Manila (120°57′ longitude, 14°35′ latitude) choose Regulus, (Alpha Leonis, 10hr08’RA +12.0°declination) nearby location underneath the star is 280km South of the city while the zenith of the city is 5 Moon’s diameter from the star and toward the Celestial North.
2. Work out the day for the star to be highest at midnight. The day is the same for all locations. It is almost Sep23rd plus the RA of the star multiplied by (365.25days/360°).
Example:
Gamma Persei is nearly overhead at midnight of
Sep23 + 3hr05*(365.25days/24hr) =
Sep23 + 46.92days = Oct23 + 17d = Nov 09.
3. Learn by heart how to identify in the sky the stars associated with the base city. The accuracy and speed of this ability is essential to avoid mistakes under adversed circumstances. Users should not confuse between stars near the ecliptic and wandering planets nearby.
4. Practice determining the time when the star passes the vertical North-South plane at the base city on that date. It is midnight minus the local advance on GMT, which is equal to longitude multiplied by (24hr/360°).
Example:
Gamma Persei passes near Berlin (longitude 13°24′) on that date ahead of mid – night GMT by (13°24′)/(15°/hr) = 0.89hr, that is at
24hrGMT – 0.89hr = 23.11hrGMT = 23hr07GMT.
5. Every day later/earlier than that date, the star passes the location (60minx24/365.25) = 3.942 min of time earlier/later. This earliness is observable at all locations including your current one. When observing the star on another day, the earliness adjustment is needed.
6. If the Sun crosses the North-South vertical plane earlier/later than at base, the chosen star also crosses the North-South vertical plane earlier/later than at base by the same amount of time.
Step 2: Field application

BrightStars0b

List of 20 brightest stars. Additional, dimmer stars are also needed to travel closer to any arbitrarily given latitudes.

7. Identify the star and obtain the time signal from GMT. Work out the instant the star is overhead the base. (Alternatively, the moment the chosen star passes overhead the base can also be determined with an accurate watch from the time it passes the North-South vertical plane of current location and the advancement or retardment of local Noon relative to Noon at base.)
8. At that moment, the star is above the nearby spot close to the base. Every degree from your zenith is 111km distance from you. The direction to the star projected onto the ground gives direction to the chosen nearby location. To obtain more accurate direction to your base when the star does not pass its zenith, you can imagine another star at some diameters of the Moon on either North or South side of the RA circle from the chosen star and use it instead. Alternatively you can add some adjustment based on the differentials on a spherical surface to obtain the exact direction to your base.
Step 3: Navigating by only stars.
9. To travel to the target location, aim for a location on the same latitude but more in the North-South direction of the current point. This makes the travel distance longer but ensures that the target is not missed in the final part of the travel. When arriving at that target latitude, aim at the target location. Keeping the selected star on the East West line when it has highest altitude will ensure that the traveler does not miss the target.
This method suggests a possible way used by desert travelers and an alternative for refinement of Polynesian method of navigation.

4. How to find the zenith point.

The navigator has to hang a long plumbing line from a point higher than his eye level, stand away from it and look at the projection of the line onto the sky. The projection is a great circle arc through the zenith.

Looking at the plumbing line from many directions gives many great circle arcs intersecting at the zenith point in the sky. The navigator may have to note its relative distances to familiar stars and draw it and the stars on a piece of paper for future reference and cross checking.

This method requires a steady plumbing line and is suitable for ground travelers when resting at night.

5. How to locate any chosen bright star in the sky.
1. Find out its position relative to the 20 brightest stars by plotting it on the star maps here from its RA and declination.
2. Work out steps starting from identifiable top 10 brightest stars to positively identify it through progressively nearer, easily identifiable, bright neighbours .
3. Use the sky maps here to practice finding it in the sky.
4. Examples.
4.1 Locating Eltanin:
Eltanin is found from star charts and the sky maps here as the brightest star near to the point of one third of the way from Vega to Dubhe (There is no brighter star in the vicinity.).
4.2 Locating Regulus:
The broom shaped group of stars (Sirius, Canopa, Orion-Rigel, Betelgueuse, Procyon) identifies their elements. Betelgueuse-Pollux forms the hypotenus of the isoceles right triangle (Procyon, Betelgueuse, Pollux, Procyon, counter-clockwise) with Procyon at the right angle. Regulus is then one distant vertex of the rhombus (Procyon, Betelgueuse, Pollux. Regulus, Procyon, counter-clockwise).

6. Notes.
1. The local true time at the base city has the Sun crossing the North-South vertical plane at 12am. The zonal time (broadcasted by local radio and TV stations in the winter) is the true time advanced or retarded so that it differs from GMT by a whole number of hours.
2. The Sun crosses the North-South vertical plane before or after 12am zonal time by the difference between the local true time and zonal time. This amount is due to the excess or shortage of longitude to the nearest multitude of 15 degrees chosen for zonal time.
3. With an accurate watch still showing the zonal time at the base city, the longitudinal increment from that of base city can be worked out by the increment in the earliness of the crossing of the North-South vertical plane by the Sun. Each increment of 15 degrees in longitude corresponds to 60 minutes advancement in noon time.
4. Near to the end of the journeys, overland navigators may apply terminal homing using mega-features such as familiar city silhouettes, mountain peaks, rivers, rock and soil formation, permanent cloud formations, existing or ancient tracks, vegetation boundaries or even smell from plants. Some traditional land travelers may even release trained eagles to home on prairies while some traditional ocean travelers may release islands spotting birds to home on islands.
RELATED SURVIVAL blogs

, posted on

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

Sky map Northern 3/4 sphere

Sky map Southern 3/4 sphere

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

image

image

, posted July 22, 2016

DirectionTimeByStars

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

Click here for my other blogs on divider43.jpgSURVIVAL

Click here go to Divider63D400 Home Page (Navigation-Survival-How To-Money).

SUBSCRIPTION: [RSS – Posts], [RSS – Comments]

MENU: [Contents][Blog Image of Contents ][Archives ] [About]