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…

Last Saturday I spent the morning in London as a guest on BBC Radio 4′s Excess Baggage. In the evening  I led a group on a night walk. The conditions were perfect. We watched as blue turned to orange. Then as the orange faded to dark blue and black we were treated as Arcturus, Deneb, Altair, Vega, Capella and others began to appear. Lurking luminously between the silhouetted branches of a two hawthorns there was a bright white light in the east. It refused to move or twinkle. It wasn’t an aircraft or a star, it was Jupiter rising to rule the sky. We looked at five different methods for finding the North Star.

Thank you to all 400 who came to a Night of Adventure in Bristol on Monday. Great cause, great audience, fun night. If this night comes to a town near you I’d really strongly recommend going if you can, there isn’t anything else remotely like it in the calendar that I am aware of. Well done Alastair Humphreys!

On Wednesday I submitted the edited copy for my next book. That night I waved a fond goodbye to All Roads Lead Home, the series which has hopefully given a couple of million their first taste of the joys of natural navigation.

Yesterday morning I was back in BBC TV Centre in London to film a short sequence for their global travel programme, Fast Track, with the presenter Rajan Datar. This morning I’m off into the hills for a private course.

In Bristol I took the opportunity for a bit of an explore, as you would expect me to. The two pictures above are of the same stone pillar. In the first one, we are looking northeast. In the second one, showing the pollution stains and algae, we are looking southwest. This is a trend that was repeated over a wide area of the city. It was great to find such a vivid example so close to the ground, normally it is worth looking above ground level for the best examples.

Late September can bring some of the best early evening experiences for those who enjoy looking upwards.

Visibility is likely to fluctuate a bit, but it looks as though we may get some of the best stargazing weather of the year over the next few nights. It promises to be warm enough to enjoy long spells outside, but without the crazily late sunsets of midsummer.

I’ll point out a few of the things worth looking for in a minute, but first just a few words about this weather.

On my courses I encourage people to take note of shifts in wind direction and how this relates to changes in weather patterns. If the weather is unseasonably warm or cold, we should expect some deviation from the prevailing wind direction, southwest.

The image above shows the UK (at lunchtime tomorrow) sandwiched neatly between a high pressure system over the continent and a couple out in the Atlantic. Winds rotate clockwise around a high pressure system and anti-clockwise round a low pressure. The net effect for us will be winds that will be coming from the south and southeast. Southerly winds tend to bring warmer air, and southeasterly winds from over the continent bring drier air than the moist southwesterly winds from over the Atlantic. Hence the warm and dry conditions.

On to the night sky…

As the sun sets the brightest stars will start to show their face. The bright yellow and orange Arcturus will appear low in the west not long after sunset.

In the south there will be three bright white stars worth looking for. Search for a large triangle that occupies the high southern sky. This triangle is made up of the three brightest stars, Altair, Deneb and Vega, from the constellations Aquila, Cygnus and Lyra. It is not surprising that sailors have learned to abbreviate this family to the nickname ‘The Summer Triangle’ or ‘The Navigator’s Triangle’.

The star of the show will undoubtedly be Jupiter, rising at about 8pm just north of east, he will be ruling the eastern sky with pomp by 9.30pm.

Many, many people will accuse this majestically bright white object of being Venus, Sirius or the North Star.

In reverse order, it can’t be the North Star as that is not a particularly bright star (and, as you may well have deduced, is in the north not the east) and it couldn’t be Sirius as Orion is nowhere to be seen. There is no way that it could be Venus, as Venus lives near the sun. If the sun has set then it is well to the west of us and we are looking east.

If you are up early in the mornings, Orion will be on watch over the southern sky, with Sirius burning brightly not far below him.

Enjoy.

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.

For three years I have been pondering how to solve a tricky riddle. There are so many people who would love to learn about the night sky, but it is very hard to organise an outdoor course for this in this country because the weather is so unreliable. I need to sort the dates for my courses at least a few weeks in advance and it is impossible to predict the conditions that far away. Also, the best times of the year for star, moon and planet-gazing are not the best times for weather. Mid-summer is great for many outdoor activities, but with the late sunsets it is not perfect for stars.

The solution, it dawned on me (pehaps I should say dusked?) is to create a club for those who are interested and then, when the conditions are right I will let everyone know where and when I will be for a couple of hours of guided stargazing. There will be no charge – as there will be no guarantees – but I should be able to give a couple of days notice in most cases and less in a few. Most of these will take place in the South Downs in West Sussex, but I will also endeavour to host a couple of nights when out and about in other parts of the UK or perhaps, in time, abroad. All you need to do to join this club is to come on one of my courses, public or private.

Last night the visibility was great and we enjoyed the nearly full moon, Gemini, Pegasus, Taurus, the Plough, the North Star, Cassiopeia, Jupiter, Cygnus, Auriga, Orion and probably quite a few others! In total we looked at five different ways of finding north from the stars and many other techniques for finding direction.

I took the picture of the moon above last night. It is full today and so was one day off full last night, but it does look quite full. It goes to show how tricky it can be to tell the difference between phases precisely. Everyone can get very close, but I do not know of anyone in the world who can, without fail, gauge the phase of the moon to the day just by looking at it. This has implications for using the slightly involved ‘phase method’ of finding direction (see the book), as for each day you are out in your estimation of the moon’s phase this can throw your estimation of direction out by 12 degrees.

Here is a bit of a red herring from a navigation point of view, but fun all the same… When I was going through my photos this morning I was about to delete an unsteady one of Jupiter (the second one shown here), when I hesitated because I spotted something that jumped out at me. Below the bright Jupiter and in a crooked line there are four stars, but just above them and to the right of Jupiter there is a very small blue smudge. This, as I hoped and suspected, was Uranus. It was not visible to the naked eye last night, but showed up on the longer exposure of this photo. A lovely small ‘discovery’ to start the day with. Not sure my name will go down there with Herschel’s though!

“He stood and carefully examined the sky, to ascertain the time of night from the altitudes of the stars. The Dog-star and Alderbaran, pointing to the restless Pleiades, were halfway up the Southern sky ,and between them hung Orion, which gorgeous constellation never burnt more vividly than now, as it soared forth above the rim of the landscape. Castor and Pollux with their quiet shine were almost on the meridian: the barren gloomy square of Pegasus was creeping round to the north-west; far away through the plantation Vega sparkled like a lamp suspended amid the leafless trees, and Cassiopeia’s chair stood daintily poised on the uppermost boughs. ‘One o’clock,’ said Gabriel.”

…

“The sky was clear – remarkably clear – and the twinkling of all the stars seemed to be but throbs of one body, timed by a common pulse. The North Star was directly in the wind’s eye, and since evening the Bear had swung round it outwardly to the east, till he was now at a right angle with the meridian. A difference of colour in the stars – oftener read of than seen in England – was really perceptible here. The sovereign brilliancy of Sirius pierced the eye with steely glitter, the star called Capella was yellow, Alderbaran and Betelgeux shone with a fiery red.
To persons standing alone on a hill during a clear midnight such as this, the roll of the world eastward is almost a palpable movement. The sensation may be caused by the panoramic glide of the stars past earthly objects, which is perceptible in a few minutes of stillness, or by the better outlook upon space that a hill affords, or by the wind, or by the solitude; but whatever be its origin, the impression of riding along is vivid and abiding. The poetry of motion is a phrase much in use, and to enjoy the epic form of that gratification it is necessary to stand on a hill at a small hour of the night, and, having first expanded with a sense of difference from the mass of civilized mankind, who are dreamwrapt and disregardful of all such proceedings at this time, long and quietly watch your stately progress through the stars. After such a nocturnal reconnoiter it is hard to get back to earth, and to believe that the consciousness of such majestic speeding is derived from a tiny human frame.”

I will try not to spoil the moment by pointing out that if Castor and Pollux were ‘almost on the meridian’ then it would be hard to see the square of Pegasus in the way that Hardy describes. I will try but fail. Rare is the fiction writer who has ever attempted to portray the night sky without betraying their lack of fundamental understanding. Hardy’s efforts are much better than most, as you might expect from a literary giant. So few writers appreciate that the stars, if described in detail, must be fixed in time, both nightly and annual, as well as in direction. There is nothing casual or random in the appearance of the night sky at all. Fortunately the errors are rarely obvious enough to spoil a good story!

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.

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.