Equinox Shadow Lines

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.

Equinoctial Sunrise

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.

The Great Shadow Stick Riddle

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 has been able to think their way to the answer so far.

The weirdest thing is that I know what the sun does during this elusive period, nothing very dramatic in short, so in theory this should be very straightforward. But it's not quite. How can the shadow go from a curve one way to a curve the other without a straight line involved? Or is there a straight line, and if so when? Because it is definitely not at the equinox, that has to be a very gentle curve in the same direction as the summer one.

Why does it matter? Well in some senses it doesn't, it is unlikely to change the fundamental ways of using the sun to find our way, but it would be, well... nice. I have spent hundreds of hours studying the sun and shadows, both physically and academically and it would give a feeling of completeness if I could just find this small missing piece of the jigsaw.

I think it may be possible to solve using a spreadsheet - horror of horrors! - but I would rather understand the world around me and resort to technology on occasion, than pretend the ignorance is somehow uplifting. It isn't. It's an intellectual irritant. I'd be absolutely delighted if someone reading this sent me the answer though. That would be a natural solution for me to a natural riddle, they need not tell me that they used some piece of whirring technology to work it out.

* On an almost related note, I do know someone who runs a small company that sells bamboo clothing.

Shadow Seeker

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.

Equinox - lovely word.

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?

Dawn Today

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.

Equal joys, Different Reasons

Everywhere I go at the moment I am reminded of cycles. Not the type that the Dutch and Boris Johnson are so keen on, no, the natural cycles. The countryside is abuzz at the moment. My sons and I love it when we come across a combine harvester and tractor at work like this. I get excited because it reminds me that we are well past the summer solstice and can start looking forward to the autumnal equinox. Their reasons are probably better.