I arrived an hour early and walked down to the beautiful beach and went for a swim (yes that really is it in the photo). I then dried myself off in the beach car park, with the car radio on as I listened to Andy Murray losing, valiantly, to Rafael Nadal. A more British experience would be hard to imagine. I walked up to the Studios to give the talk, watching a kid go beserk after dropping an ice cream and feeling the sand between my toes.

Whilst very vaguely on the subject of swimming, the Independent invited me to be on their Best 50 swimming spots in the UK panel. The results can be found here.

Last night, shortly after 10.30, I took this photograph of the moon rising above the woods and emerging from behind thin clouds. It looks very much like a full moon, but is actually one day after full, a waning moon. It does highlight the difficulty of judging the phase of the moon accurately.

From an aesthetic perspective there is no need to be able to judge the moon’s phase, but if you are trying to use the ‘phase method’ of finding direction from the moon then it is vital. I go into a lot of detail of this method in the book, because it is very satisfying but no less challenging. In a nutshell, you can work out direction from the moon if you understand where it is in its cycle relative to the sun (its phase). In the simplest possible example of this method, a full moon is opposite the sun, so if the sun is setting then the full moon will be rising and vice versa. But it gets so much more challenging, interesting and fun at every other stage!

My thanks to everyone who came to my talk last night at the Weald and Downland Museum. What a wonderful place to spend a summer’s evening, I recommend a visit to anyone who has yet to sample its delights.

On a different note, I received a fascinating letter recently from someone who has read the book. They wrote to me with an unusual observation.

I have touched the phenomenon of the ‘green flash’ at sunset in this blog and elsewhere, it is well documented and well heard-of. My correspondent is keen to learn more about something different and since I have been unable to solve the mystery, I promised to publish the extract from his letter here in the hope that a blog reader may be able to offer an insight.

“...My second point is the green flash you mention. My experience was quite different from the quick flash most people seem to see and perhaps you can shed some light on it. I was sailing in Caribbean and we were at anchor in a bay looking west. I was the only one on deck. I watched the sun set, and perhaps a full minute went by when suddenly, as if someone had switched it on, just where the sun had disappeared, a green fan of light sprang up, rather like a wide angled searchlight, the point of the fan below the horizon so that the base appeared to me to be perhaps 4 degrees in width. It spread well up into the sky so that the arc of the top of the fan was perhaps 20 degrees wide and about 20 degrees above the horizon. I measured the angles with my fist. The light was a light grass green but the stars showed through it clearly. It was quite lovely but I was sure it would disappear in a trice and my camera was below, so I did not want to break the moment and just sat there. But, to my surprise, it did not disappear. I sat there for what seemed several minutes but was probably just two; then it faded away as fast as it had come. Has anyone else reported seeing something similar? Obviously I should greatly value any knowledge you may have of it.”

I’d be delighted if any blog readers can shed any light on the mysterious green sunset fan.

I did not manage to see or capture the flash, but peering out across the Persian Gulf at the anchored ships, feeling the cool westerlies coming off its waters as the heat of the day faded… is not a bad way to endure a fruitless search.

It is often very difficult to see the sun clearly at the moment of sunset due to clouds or haze, but there are times when, if the sky is clear, the air is dry enough and the horizon is an ocean, then the sun can be seen very clearly all the way down – as in this case. These conditions do not congregate frequently in the UK, which may well be one of the many reasons we associate sunsets with holidays.

Researchers from the IE University School of Biology in Santa Cruz, Spain, have found that the male bustards align themselves with the sun when trying to attract a female. Their white feathers, the bustard’s equivalent of an Armani suit/Ferrari/pair of Reeboks – delete as applicable, show up better when aligned to catch the sun’s rays. Dr Tommaso Pizzari, an ornithologist from Oxford University, observed that although it made the birds more vulnerable to predators, it certainly made them more visible to females. ‘That’s why we think these puzzling traits evolved and are specific to males.’

Although the bustards have been found to do this more dependably in the eastern morning sunlight, the human animal is more likely to be found trying the same tactics over a cocktail umbrella pointing towards the western sunset.

The BBC website has more, but then so does everything around us – there isn’t much nature without sex.

The picture was taken looking northeast. The very perceptive will have noticed that there are molehills in the foreground and that they are in the shaded ground, very possibly not a coincidence. Something I touch on in my book. Oh you tease, you!

A roe deer jumped across the path in front of me as I climbed the hill and there was the red breast of a robin waiting on the branch of an ash, modelling part time for a Christmas card perhaps. The first thing that struck me on reaching the windmill was the large patch of green grass shaped like a cone to the south-southwest. A distinct snow shadow tucked away from the heavy snows of the night before. It was a clue both to the wind direction of the night before, but also the strength of the wind. The snow must have fallen in something close to a storm as the shadow stretched quite far from the base of the windmill, suggesting strong winds. This had led to some unusual effects elsewhere as well. In light winds the snow tends to accumulate on the lee of obstacles like trees, but when the wind is strong it is plastered onto the windward side where it sticks. From a navigational perspective it does not matter hugely whether the snow has stuck to the leeward or windward side predominantly, because once the orientation has been identified it will be consistent over wide areas. In fact the north-northeast of the trees all the way down the A roads from London to Chichester had shown this trademark strip of white.

The wind direction had not changed noticeably since the snow fell and I sheltered in the relative warmth of the lee of the windmill with a flask of hot chocolate, venturing out every few minutes to take photos. The two day old moon was the first object to appear after the sun, followed quickly by Jupiter in the south.

This morning I was sent this photo, by Fred Smith, a retired airline pilot who came on one of my RGS courses a few months ago and who now lives in the Caribbean. It shows the same two-day-old moon of yesterday, which is the same phase when viewed from all over the world, but the orientation changes with latitude. The faint star just visible below the moon is Mercury, which had not been visible in the cloud near the horizon in Chichester. More often than not an ‘evening star’ will be Venus, but on this occasion Mercury is far enough from the sun and Venus is hidden in the bright glare of the sun itself and impossible to see.

Pirsig takes on some massive philosophical beasts in both books, but the freshness of his approach can sometimes be seen best in the way he deals with more simple and natural phenomena. This is his take on the fabled ‘green flash’ of the setting sun,

‘When Phaedrus started to read yachting literature he ran across a description of the “green flash” of the sun. What was that all about, he wondered. Why hadn’t he seen it? He was sure he had never seen the green flash of the sun. Yet he must have seen it. But if he saw it, why didn’t he see it?

This static filter was the explanation. He didn’t see the green flash because he’d never been told to see it. But then one day he read a book on yachting which told him, in effect, to go see it. So he did. And he saw it. There was the sun, green as green can be, like a “GO” light on a downtown traffic semaphore. Yet all his life he had never seen it. The culture hadn’t told him to so he hadn’t seen it.’