This instrument is as simple as they get: it works by forming a triangle. If you know the base of a triangle (the fixed length of twine from eye to instrument) and you know the height of the triangle (the number of fingers counted up from the horizon), then you have a fixed angle to the horizon. This is the ancestor of nearly all navigational instruments prior to electronics. (In fact the triangulation used has a lot in common with the way GPS works, but that is another story.)

How does it work in practice?

Here’s the simplest example: the Pole Star (Polaris, North Star) will be the same angle above your horizon as your latitude. At the North Pole it is vertically overhead and you are at 90 degrees north. At the Equator it sits on the horizon and your latitude is 0 degrees.

On a more practical level… Imagine you set out west from a desert camp on a long journey west into the Sahara. If you measure, as accurately as possible, the number and fraction of fingers that the Pole Star is above your northern horizon then you have a measure of your latitude. You can confidently explore the desert for as long as resources allow, then, when it is time to head home you line your kamal up with the Pole Star. If the star is higher (more fingers) you are north of your camp, if there are fewer fingers you are south of it. All you do is head north or south until the right number of fingers line up with the star and then head back east. You will bump into your camp. If you have been skilful enough! (The same of course applies to any ocean journey).

There are lots of slightly more convoluted (and fun) ways of using this simple instrument, but that is the crux of the matter.

Once this makes sense it is very easy to see how the whole history of navigational instruments developed. They mostly boil down to a desire to measure first angles and then time more accurately. The backstaff, octant and sextant are just the pernickety (and more accurate) grandchildren of the kamal.

You can make a kamal at home using cardboard and string. I nearly mentioned double-sided sticky tape then, but its too simple for even that. Bad luck, Blue Peter! With a bit of luck they’ve already got one somewhere, one that they made earlier…

Finding South Using the Stars

In the northern hemisphere Polaris, the North Star, tends to get all the attention when it comes to finding direction using the stars. There is a good reason for this: it is easy to find and is very accurate. In the southern hemisphere the Southern Cross is used to find south and Polaris is not visible. But what about finding south in the northern hemisphere? The easiest thing is still to find Polaris and then look in the opposite direction, but what if we want a method that actually shows us south itself. Here is a nice simple and very unusual method that I invented a few years ago, which you can try this evening.

First you need to find the constellation Leo. It is a nice, big and easy to identify constellation which, unlike some constellations I can think of, looks at least a little bit like how you would hope it does: ie. like a lion. If you are struggling then tonight it will be about three extended fist-widths to the left of the moon. Having found Leo, next you need to find two little-known but beautifully named stars, Chertan and Zosma, that form the rump of the lion.

In the first image, Chertan is the star that has been ringed, and Zosma is the one directly above it. When Zosma appears directly above Chertan, as in this picture, you must be looking due South. Have a look as soon as the stars come out tonight.

Getting Advanced…

That is a nice, quick and simple method for using Leo to find south, but it does have one big drawback: it only works at certain times. I have devised a more advanced method for using Leo to find south that will work at any time and from anywhere that you can see Leo, but be warned this is a bit beyond beginner’s level so only read on if you are an experienced stargazer already or if you are up for a challenge!

We need the same two stars as before, Chertan and Zosma. Next what we do is extend a line from Zosma down to Chertan and keep it going until it hits the ground. If this is a vertical line, then, as we saw earlier, this will be due south. But most of the time these stars won’t form a perfect vertical line (they will wheel across the sky like the hand of a clock) and so what we need to do is continue their line to a point underground. The point underground needs to be the same angle below the horizon as your latitude. On the south coast of England my latitude is 50 degrees north and so I am interested in a point that is 50 degrees, (five extended fist widths) underground.

Wherever the extended line from Chertan and Zosma gets to this depth will be due south. All you need to do is find the point on your horizon that is vertically above this underground point and that will be due south.

Since you can find direction using Polaris in many more straightforward ways, this method is really just for fun, unless you are very unlucky and Leo is the only constellation that has not been obscured by cloud.

Why this method works:

Whenever we are using the stars to find north or south, we are looking for ways to find the north or south celestial poles, the two points in the night sky that are directly above the Earth’s North and South poles. If we look towards a point in the night sky that is above the north pole we must be looking due north. The same logic applies to the south celestial pole, but because we are in the northern hemisphere the south celestial pole is invisible, it is underground. But we can imagine where it might be and actually work out where it must be using the stars. The point on the horizon that is directly below the north celestial pole, ie. below Polaris, is due north and the point directly above the (underground) south celestial pole must be due south.

I set off as the last light from the sun faded in the southwest. Cassiopeia and Cygnus neatly sketched out north for me, even when Polaris was well hidden. When moving south I used Jupiter and Aquila.

Four hours later I returned, having spent nearly all of it alone, in beech woodland and without using a torch. Moving at times with my left hand extended out to fend off inquisitive lower branches, I covered about six miles; this was no race.

In every woodland walk there are times when you feel the forest is on your side and times when it is inviting you to make haste the exit. When the sun has gone down, the trees never lose their ability to thrill and scare.

The only light I used all night was the single flash from my camera to catch my nemesis. I closed and shielded my eyes, to protect my night vision, and then pointed the camera and ‘shot blind’. This picture, which I did not look at until reaching the end of my walk, must have been of some ogre, a menacing hunched figure, one who crouched silently by the path of those who were foolish to walk alone at night in the woods. Turns out it was a tree stump.

Or perhaps it only turned into a tree stump when my camera came out? Heisenberg wrote of stranger things and called them physics.

My sources tell me that the first is a Magpie Inkcap (Coprinopsis picaceus) and the second is Green Elf Cup/Wood cup/Stain (Chlorociboria aeruginascens).

My thanks, in no particular order, to: Nick Weston, Brian and Ross Gardner.

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A thousand apologies for that title.

Seriously now, are there any fungi experts out there?

Yesterday I came across these two rather fun specimens during a family walk in our local woods. Thought one was a Panther cap, but looks a bit too ‘pointy’ for that. The blue one is beautiful, but not one I can even guess at. I’m assuming it is a fungus, but could be a lichen at a stretch I suppose?

If anyone knows someone in the know please could you waft these images under their expert noses. Much obliged. Credit will be given. My email address is here.

On a different subject, my thanks to James Garrett for booking a private course for 15 people on Saturday afternoon and to all those who came. We set off from Ditchling Beacon on top of the South Downs and after some exploration and investigation of an area rich in natural clues, we were able to wrap the day up with Jupiter, then Capella, Arcturus, Deneb, the Plough, Polaris, Cassiopeia. Way to finish. I was so glad to have an excuse to be on top of the Downs. Thanks!

Orion and his sword were first to offer their greetings and then I noticed Jupiter still visible in the southwest. Sirius, Betelgeuse, Capella, the Plough and Polaris sketched out some order in the celestial sphere.

The moon was close to setting and was lighting up rows of fluffy cumulus clouds on their western edges. As time passed the clouds lost their bright white western edges, but gained pink and orange eastern ones. They moved sedately towards the northeast, signalling the start to a fine day. (Photo to the right was taken a few minutes ago.)

I adore the Witterings in winter, the barbecue and beach towels may have to stay at home but it is invigorating to get blown along on miles of abandoned sand. In between games of hide and seek amongst the beach huts, games of football on the sticky sand and races to pieces of seaweed, I noticed some interesting patterns in the sand.

This photo shows how there tend to be broad ripples parallel to the coastline itself, but closer inspection reveals more subtle patterns and these can be used to decipher the action of the water and therefore yield more clues to direction. The ripples of sand fan out over the small hills that are exposed at low water. There are tight-packed parallel ridges where the water action is uniform, but a more confused system of diamonds where incoming water meets the returning undercurrent from earlier waves. All of these patterns can be used by walkers in low visibility to orientate themselves, if the sound of the water is not helping, but they can also be used by divers searching for a clue to the direction of coast in low visiblity.

Tristan


I managed to rope in a friend at the end of an evening’s BBQ and together we plumb-bobbed Polaris, set out two posts and then strung a string between them. We checked with a compass and, despite the evening’s beers, we were actually almost spot on!

The next day we checked the shadow at 1.00 (12 noon GMT) and found this lined up on our string. Impressed or what!

Richard

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Hi Richard,

I can see I’m going to need to come up with some sort of merit/badge/star system just to complete the back to school experience!

A link that I will have mentioned on the day is here:

http://aa.usno.navy.mil/data/docs/AltAz.php

If you plug in your latitude and longitude, it will give you the altitude and azimuth of the sun (or moon) for a whole day by GMT. Due south is often very close to clock midday, but it can wander off it depending on your longitude and because of something called the ‘equation of time’.

All the best,

Tristan

Tristan

Many thanks for a fantastic day yesterday.

I learnt so much and was stimulated also by the opportunity to apply what I did know to a new “problem solving” challenge! I checked out the moon last night and located Polaris and was quite comfortable that it was NOT directly above my head as I always imagined it might be! (I do need to re-set the weathervane and I think I’ll use Polaris to do this!)

The principles you taught will add another layer to my enjoyment and connection with the great outdoors. So rather than just walking through it and looking at the views I’ll be able to read more off it. Natural Navigation is a key to unlocking a fascinating text in the Earth’s rich library.

Thanks again for a very inspiring day – just off to check the lichen and moss on the trees in the garden!

Richard W (Cambridge)

This morning I thought it would be nice to give it credit for being more than just a signpost. It is Ursa Major, the Great Bear and has featured in literature and art for as long as words and pictures have been recorded. Homer, Shakespeare and Van Gogh have given it the time of day.

The first thing we can do if we want to give it a second thought is to look to the middle star in the Plough (saucepan to some) handle. This can be seen clearly as a double star. It consists of the brighter Mizar and fainter Alcor. I took this photo early this morning, my fingers aching as I pried the frozen gate latch from over a post. One must suffer for one’s art. If you click on it and look at the expanded version you will see the double star.