2013-03-31
Happy Easter! When is Easter? Today, is the short and not very helpful answer. The longer, more useful answer is: Easter is always the first Sunday after the first full moon after the vernal equinox. This explains why it is never the same from year to year. The calendar date of the equinox will only move by a day or so, but the timing of the next full moon can vary by as much as 29 days. There is an interesting page about the history of this calculation on this page.
2012-07-30
In the desert of western Peru there are the remnants of a civilization that still holds many mysteries. Archaeoastromomers are able to deduce a few things about the ancient complex at Chankillo, from the alignment of 13 towers. The towers form a north-south line, but this is not that unusual in ancient buildings. The thing that sets these towers apart is the fact that they span the annual range of sunrise, from winter or June solstice (northernmost tower) to summer or December solstice (southern tower), when viewed from a certain point. There is a good view…
2011-10-27
Have you had that feeling recently that the season has not so much shifted to autumn, as snapped? There is a time each year when we get this feeling and its suddenness not purely psychological, it is because we witness the most dramatic changes in the Earth-Sun relationship at two times in the year: spring and autumn. Some of the things that we tend to assume change gradually, actually don't at all. On this blog I have mentioned that the bearing of sunrise and sunset change most dramatically at the equinoxes, in March and September, and briefly…
2011-01-02
Happy New Year!At times like this, I sometimes wonder what the Earth and Sun would say to each other if they could talk. They would watch us celebrating this annual moment at such an arbitrary time...Sun: I could understand a party at either solstice...Earth: Yes, or one at either equinox. Would make good sense...Sun. Quite. But to pick a day about a week after one solstice...Earth: Very strange.Sun. Yes. They are a very strange lot.In this picture of a beech tree in Wiltshire, we can see both moss and lichens thriving in the moist air close to the ground. Water…
2010-03-20
Happy Spring Equinox!My plans this morning, as announced in the Telegraph, were to head to the top of a hill and catch the sun rising due east. Sadly, the air is cooler than its dewpoint... the humidity is greater than 100%... there is a low level of nimbostratus... however you want to put it: the weather is not very good and the visibility is terrible.Had I been able to see the sun it would have risen due east. The vernal and autumnal equinoxes being the only two days of the year when the sun rises due east.Something that you…
2010-03-03
This photo of the roof of my home tells a story of the sun's journey.The morning shadow from the dormer window is retreating and the sun is reaching more of the roof with each minute. The frost from the night before is thawing in the warm light. It is also forming a very simple shadow compass. At this time of year the sun rises very close to east and the direction that the frost is retreating will be west to east. The protruding 'nose' of frost near the top of the roof can be joined to the jutting part of…
2010-01-21
Just back from a little research in the New Forest. While I gather my thoughts about all the natural clues to wayfinding that the Forest revealed I just thought I'd let you know about a great website from a different part of our island. Stonesofwonder.com is a very informative guide to the prehistoric sites of stone monuments of Scotland, all arranged with celestial observation or inspiration in mind. There is information about the location of sites like Ardachearanbeg, Clochkell, Cultoon, Finlaggan, Drumtroddan, Clava, Callanish and Stillaig, to name a few, and details about their relationship with moments like…
2009-09-25
An engaging group for the Beginner's Guide to Natural Navigation course at the Royal Geographical Society yesterday. Diverse in age and interests as always. When we were discussing the difference in the sun's behaviour between the solstices and equinox it felt more poignant that we are so close to the autumnal equinox itself. We looked at a model of the Earth orbiting the sun, then shifted our attention to shadows. A couple of days ago I took advantage of the sunshine to practice what I preach.This chalk line in this picture shows the shadow tips joined over a period of…
2009-09-17
Another cracking dawn. There were four Roe deer in our neighbouring field, but sadly they scarpered before I got to my camera. I don't actually have a brilliant lens for wildlife, so you have been spared a photo of four brown smudges in a brown field.Only a few days of this solar season left, the autumnal equinox is on 22 September. This means that in the UK there are only four more days when the sun will have any north in it at all for another six months. At times like this, close to the equinox, the point on the…
2009-08-17
Nice article on the Beeb website about the Saturn equinox. A succinct definiton of 'equinox' in the article too:'Equinox is the moment when the Sun crosses a planet's equator, making day and night the same length.'I forgot to mention that I delivered the manuscript of my book to my publishers, Virgin Books, three weeks ago. It is an exciting moment, a good line in the sand, but far from a terminal one. Work will continue on it until about November probably.
2009-05-05
During a private course yesterday we spent some time looking at the effect of the wind on trees and grass. We also looked at the lee effect, when leaves and other natural drifting materials accumulate on the lee side of obstacles.This is something that I am both more sensitive to and wary of since my trip to the Sahara in March. The lee effect there puzzled me for several days until a sandstorm blew in and blotted out the sky. Ironically it clarified things mentally. There is a difference between a prevailing wind and wind that has a huge short-term…
2009-03-31
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.
2009-03-23
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…
2009-03-21
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.
2009-03-19
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…
2008-09-28
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.
2008-09-22
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?
2008-09-15
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.
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