The natural Navigation: The Right Course, Naturally

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…

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It’s 8.15am this morning out on the Downs and this sheep’s shadow tells us that we are looking south. Her wool, or ‘sheep fur’ as some would have it, is blowing from the same direction as the sun and gave me a constant reference all morning.

On a completely unrelated note, there is an article about the RGS in today’s Telegraph that I have somehow appeared in.

In this photo you can see the dew that the sun has not yet burnt off. The shadow itself is mostly moving right to left in this picture, leaving the thin band of wet wood in the shade all the time. This thin band is a rough east-west line at all times of the year, but quite an accurate one at times like this, close to the spring and autumnal equinoxes.

The small patch of moisture that is in the sun reveals the direction that the shadow is shortening, a crude north-south line as we near the middle of the day.

For the next six months the sun will always have some south in it when viewed from Britain. It will rise south of east and set south of west until the 20th March 2009. Its shadows must therefore always have some north in them. This picture was taken at 9.35 this morning, by which time the sun is fast approaching south-east and my shadow is well on its way to north-west.

Random fact for the day: sun compasses were still being issued to the military for the first Gulf war in 1991.

This is a picture I took about half an hour ago and it is one of those that might be dismissed by those not trained in the dark arts as a ‘typical English country scene’. With closer inspection it yields navigational fruit aplenty.

The foreground shadow confirms that the sun is no longer visible from this viewpoint, but the direction of the early evening sun is easy to detect from the long shadows in the middle ground. We are therefore looking south.

The smoke from the two fires reveals that the wind is light and variable. In the space of little more than a hundred metres it goes from next to nothing to a light north-easterly breeze.

In the top left of the picture, just above the tree line the south coast sea can just be seen. It is running from left to right, or an east-west line, which…

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Trying to be positive when there have only been a brace of sunbeams all August so far, I have been tinkering with the overcast shadow method. The theory being that plenty of light filters through the overcast clouds and that a thin blade can be used to average the source of this light, ie. the sun. It is better than nothing, sometimes, but it is important to be aware that the shadow will be thrown opposite the brightest light and there are no guarantees that this is where the sun is. Uneven cloud or tree cover are just two of the things that can throw it completely.