The natural Navigation: The Right Course, Naturally

As we move on away from the equinox I thought I would post this photo of the lines made by the shadow tip from a stick (or in this case a kids swingball!).

These two lines are from the shadows approaching noon and only one day apart. Since it is the equinox, they are near exact east/west lines. The gap between the chalk lines is at its greatest at the equinox and closes to near zero at the solstices.

On a slight tangent, it was a very similar method, ie. measuring the length of the shadows that helped the ancient Greeks come up with their first estimates of the size of the earth.

It is the morning after the equinox and not a bad one either. The sun rises due east on the equinox, but the daily difference is at its greatest at this time too so we have already moved north of east.

In this picture the horizon is well above sea level because of the hill, so we have to bear in mind that the angle the sun makes to the horizon will be 90 degrees minus our latitude, ie. our colatitude.

Although I occasionally get labelled as Mr. Anti-anything-modern-and-would-rather-eat-a-pair-of-hemp-pants-than-use-a-GPS*, the truth is different. I do use a GPS, quite regularly in fact and always take one on serious walks, even if I don’t use it. I was able to use it to test natural navigation skills in the Libyan Sahara recently.

Soon I am hoping to use technology to solve a riddle that is proving elusive to both natural observation and thought. That is the shape of the a shadow stick’s arc as it goes from one side of an equinox to another. It is too subtle for me to gauge from stick and chalk efforts in my back garden. The answer is not in any of the many books and articles that I have on astronomy, ancient or modern. I have put this little riddle to dozens of good minds over recent months, some of them professional scientists, and no-one…

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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.

At 15.44 (GMT) this afternoon the sun crosses the celestial equator. It is the autumnal equinox. What on earth has that got to do with the price of toast, I hear you ask. Well amongst other things it means that today is one of only two days this year that the sun rises and sets due east and west.

Equinox, mmm, equinox, lovely word. Did you know that it comes from the Latin words for ‘equal’ and ‘night’, because on the equinoxes everywhere in the world experiences the same amount of day and night-time?

The Natural Navigator’s day often starts with a quick check that the sun is rising roughly where it should be – blog readers will be the first to know if it doesn’t! As this picture shows it is not always a chore and the time that our youngest is getting up each morning certainly helps make sure I’m ready.

This will be the last week this year when the sun rises north of east and its change as it heads south each morning (and evening) is at its fastest at this time of year.