Lat / Long without a GPS

[Wooky]

In the late 90's while working in the Central Kalahari of Botswana we met a family (single vehicle) who were attempting a south to north crossing of the reserve.They had maps, compass and GPS but a few days out on their adventure the GPS died leaving them to navigate by map and compass alone which in a featureless landscape is close to impossible.

Sure on a trip like this we are quite possibly in a group of vehicles, all with a GPS, or we could / should pack a spare but what other means would we have of determining or current position without a GPS. This over the years has become an on again - off again pet project.

Thanks to the Corona lock down I have finally got around to typing up a simple celestial navigation method using what we would (well most of it anyway) have in our vehicles on an overland excursion.
If you are interested in having a go / find this useful see the attached PDF.

Accuracy is very dependant on how diligent you are in your setup, time keeping and measurements. I have got it down to ~2km of my actual GPS position but normally would work on an accuracy of ~10km.

[Mad Manny]

I'll have to check this out.
Sounds interesting...

[Wooky]

Post some feedback when you do.
Suggestions for alterations to the instructions also welcome.

Ultimate goal is to have a printable document, that only cost a few pages and some ink, that you could have along in the vehicle as a back up (if you are spending time in places with few land marks to use) and the GPS fails...... well that is the idea anyway.

[Wooky]

Updated instructions now in post #1

[AndreasR]

This looks very interesting. Definitely going to give a try.

[Wooky]

This looks very interesting. Definitely going to give a try.

Please post feedback when you do.

[BushWacker]

... Im sure there’ll be a way with my
fancy Stanley (Brunton Style) Compass ...

[Wooky]

Nice compass. Those are worth a fortune now days.

In about 99% of places we would ever travel there would be sufficient topographic features to orientate yourself with a topo map and compass.
However in completely flat terrain like the CKGR there are no topo features to take a bearing on and some of the topo map sheets don't even have a contour line on them (at 20m interval).

The other place orientation with map and compass is problematic is in flat wooded areas like the northern Moz coastal belt forests.

In these areas, without a way of fixing your position, it is easy to head off in the wrong direction.

[BushWacker]

... well ... then my approach would be
to locate Sigma Octantis at a given time
via the vertical line through the intersects
of the cross and its pointers construct ... and careful surveillance of that vertical line
with my trusty old Zeiss binos...
... to establish celestial orientation
... ‘ Brunton’ should provide reasonable MagNorth orientation esp via two readings
taken say 1 visiual linear km apart ...
If ‘known’,Celestial & Magnetic orientations
should permit Lat & Long co-ord est ?

[Wooky]

Establishing direction is the easy part.

To do any decent celestial nav star sights you are going to need a few things.
1/ A device capable of reading angles down to arc seconds, so a bubble sextant.
2/ A current nautical / aeronautical almanac to get the current date and time reduction tables for that particular star
3/ A firm grasp on how to use the above and apply the necessary corrections for things like atmospheric diffraction etc.

I am not sure how close you would get but would be interested to hear how close you got if you give it a go.

[Wooky]

Also keep in mind that each degree of Lat or Long equates to ~111km on the ground.
So even a minor error in the actual star sight will equate to a very large uncertainty on the ground

[BushWacker]

... LOL ! ... I’m sure you're right Wooky !
My ‘approach’ was a bit tongue in cheek...

I see 1 deg lat is about 111 km
and 1 deg Long is about 85 km ...

... so few degs out in the bush
can be long way off the mark...

[Wooky]

... LOL ! ... I’m sure you're right Wooky !
My ‘approach’ was a bit tongue in cheek...

I see 1 deg lat is about 111 km
and 1 deg Long is about 85 km ...

... so few degs out in the bush
can be long way off mark...

A few years ago I actually borrowed a sextant and tried my hand at star sights.
Lets just say I am very glad we were not relying on my position fixes for our survival.
Watching the youtube clips and reading the textbooks makes it sound easy

[Wooky]

I see 1 deg lat is about 111 km
and 1 deg Long is about 85 km ...

Lat stays fairly constant at around 111Km
Long actually varies. At the equator is is also ~111km but by the time you get to 40 deg North or South is drops to ~85km and gets even smaller the nearer you get to the poles (Zero at the poles)

[BushWacker]

... agreed ...! And I think 1 deg longitude distance can be calculated wrt latitude and distance at equator.

... but you got me thinking now ...

... if I mount a hunters telescopic sight (with cross-hairs)
along one arm of my degree scaled inclinometer
the other arm of which, with leveling bubble, on my plane table
and use a plumb line as a vertical indicator
and align the whole contraption with my compass against a sighted star ...
might get more accurate orientation readings !

... but will still need all those ref-tables and the know-how etc
... but still won’t get arc second accuracy !!!