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.jpegwpid-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.

Reference

[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 , www.hurstwic.org, http://www.hurstwic.org/history/articles/manufacturing/text/norse_ships.htm

 

RELATED SURVIVAL blogs

, posted on

 

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

Sky map Northern 3/4 sphereSky map Southern 3/4 sphere

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

imageimage

, posted July 22, 2016
DirectionTimeByStars

 

Navigating with an AM MW radio receiver, posted January 17, 2017The Scorpius constellation, posted January 8, 2017, The Orion constellation., posted December 26, 2016, Rice as emergency food.Using GPS in off-grid situationsSlide Sky-Disks with grid masks showing azimuths and altitudesSlide 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]

Advertisements

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

  1. fantastic publish, very informative. I ponder why the opposite experts of this sector don’t notice this. You should continue your writing. I am sure, you have a huge readers’ base already!|

    Like

  2. After looking over a handful of the blog articles on your site, I honestly appreciate your way of writing a blog. I saved as a favorite it to my bookmark site list and will be checking back in the near future. Take a look at my web site as well and tell me what you think.|

    Like

  3. A fascinating discussion is definitely worth comment. I do believe that you ought to publish more about this issue, it may not be a taboo matter but generally folks don’t speak about such issues. To the next! Kind regards!!|

    Like

  4. I believe that is one of the so much important info for me. And i’m satisfied studying your article. However wanna observation on some normal things, The site taste is ideal, the articles is actually great : D. Good job, cheers|

    Like

  5. Very nice post. I just stumbled upon your weblog and wanted to say that I have really enjoyed surfing around your blog posts. In any case I’ll be subscribing to your rss feed and I hope you write again very soon!|

    Like

  6. After looking over a few of the blog posts on your site, I honestly like your technique of blogging. I saved as a favorite it to my bookmark website list and will be checking back in the near future. Take a look at my website as well and let me know how you feel.|

    Like

  7. Aw, this was an incredibly good post. Taking the time and actual effort to make a top notch article… but what can I say… I hesitate a whole lot and don’t manage to get nearly anything done.|

    Like

  8. Do you have a spam problem on this site; I also am a blogger, and I was wondering your situation; many of us have created some nice methods and we are looking to trade techniques with other folks, please shoot me an email if interested.|

    Like

  9. A motivating discussion is worth comment. I believe that you need to publish more on this subject, it may not be a taboo subject but typically people don’t speak about these topics. To the next! All the best!!|

    Like

Comments are closed.