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by Wal Bowles


Have you ever encountered a situation when, like a wide eyed child watching a magician's sleight of hand for the first time, you just do not believe what you are seeing?

It was yet another Adastra experience, which was unreal for me at the time, but for which, I was particularly grateful, especially in later years.

It was within a few days of 21st. December 1962, the longest day of the year in the southern hemisphere, and our crew was flying on a magnetometer oil survey operation west of Rockhampton. We were flying quite early in the morning, as was usual, to make the most of smooth flying conditions. Any turbulence at all would upset the magnetometer trace, so we would always aim to be airborne at first light - about 20 minutes before sunrise.

So there we were, settled down at 1000 feet above ground level in Hudson VH-AGE, on our first run towards the east, flying along the Tropic of Capricorn on the longest day of the year (in the southern hemisphere) and the sun hadn't yet risen. Enjoying the morning, tracking accurately with little wind drift on a track (true) exactly from west to east and thinking that the Tropic of Capricorn is the southernmost trajectory of the sun across the earth's surface, I was expecting the sun to rise precisely on our nose. The eastern skyline became lighter and lighter as the time for sunrise approached and then the rim of the sun's disc appeared over the eastern horizon - but it wasn't on our nose! It was a good 20 degrees towards the southeast. It was an unbelievable situation. I turned to our navigator and asked: "Where are we?" I had been monitoring the photo-mosaic map and his reply was what I expected. "We're spot on track." I confirmed with him that the runs were exactly in a true direction, east to west, and then asked: "What's the sun doing over there?" He replied: "Buggered if I know, but we're where we ought to be."

At the time it was, for me, an unreal situation. It was as if my internal world was suddenly turned upside down and the principles of physics were totally awry. The sun simply couldn't be where it appeared to be - or so it seemed. It was as unbelievable to me as if you looked out your bedroom window one morning to find that the sun had risen in the north. I needed to put this episode of unreality on hold, to believe that the navigation was spot on (and our navigator had never given me any cause for concern previously) and get on with the job. I would try to fathom what was happening with the position of the rising sun later.

Everyone knows that the sun rises in the east, sets in the west, and never tracks further south than the Tropic of Capricorn, which it does on or about 2lst December each year. In the northern hemisphere, 2lst December is their shortest day. June 21st is their longest, and the sun never tracks further north than the Tropic of Cancer - it's all basic to our geographical understanding. I had completed a couple of pilot navigation courses and the strange behaviour of the sun I was witnessing had never been mentioned - and of course here is where I show my astounding ignorance, though I suspect this ignorance might not be limited to me!

I figured that it had to be true - the Tropic of Capricorn is the southernmost trajectory of the sun across the earth's surface, so what was I missing?

Of course! The sun is directly over the Tropic of Capricorn on 2lst December, (or thereabouts) each year, but it is over the Tropic at midday, as the world turns, in each location along the latitude 22 and a half degrees south. (The Tropic of Capricorn is twenty-two and a half degrees south and the Tropic of Cancer is twenty-two and a half degrees north). The earth rotates once every twenty-four hours - 90 degrees every 6 hours. That is, if we are anywhere along the Tropic of Capricorn and looking towards the sun at sunrise, we are looking at the sun about 6 hours before it is directly overhead. And if we look towards the rising sun when it is 90 degrees before it is overhead, we also need to take into account that we are observing the twenty-two and a half degree inclination of the earth. Thank heavens! My confidence in physics was restored and my understanding of the ways of the world took a leap. And of course this thinking applies not only to the Tropic of Capricorn but also, with some variation, to every latitude on the planet.

And how did this understanding lead to my later gratefulness?

In the year 2000 my wife and I moved into a house we had had built. Fortunately our house building area was not restricted and we could site the house in any direction. Living in the mid north coast area of New South Wales which has a wonderful climate, though tending to be warm for much of the year, we wanted to make the most of insulation against heat. We designed the house, having in mind that, in summer, the sun rises 22 and a half degrees south of east and sets 22 and a half degrees south of west. That is, in mid summer, the sun will shine on all four walls at some time during the day, even with a generous eaves overhang. Even the southern wall of a rectangular house, aligned with the cardinal points of the compass, will have sun shining on it at some stage in the warmer months, and we preferred the cooler, morning sun to be shining on the southern wall longer than the warmer, evening sun. We aligned the longer axis of the house in a northeast southwest direction. (It's actually aligned almost exactly as is the actual direction of the 07/25 runway at Sydney Airport -about 062/242 degrees magnetic - about 074/254 degrees true. Magnetic variation is about 12 degrees east). This allows the cooler morning sun, which first appears over the horizon on the longest day at about 112 degrees (true) to shine on the south-eastern wall for considerably longer in mid-summer than the hotter, western sun, which sets over the horizon at about 248 degrees (true) on the longest day. The hot western sun is shining at a low slant on the south eastern wall each evening for the few weeks it takes while moving between its southernmost trajectory of 248 degrees (true) until moving further north than 254 degrees (true) - the direction of the house site. (The trajectory is relative of course - the earth, tilted on its axis by 22 degrees, and is rotating.) As well, the house is designed with the laundry, pantry and bathroom along the south-eastern wall so that, as well as ample roofing insulation, these rooms provide further insulation for the living area, which makes the house noticeably cooler in mid summer (I must admit that the house works well both in winter and in summer - and more by good luck than good management. In winter the sun slants into the north- western windows and warms the tiled concrete floor, which acts like a heat sink. We find there is no need for air conditioning or heating.) I guess we could have saved ourselves this thinking feeling and paid an architect - but we would probably have drawn the short straw and chosen an architect who was unaware that, in mid summer, the sun rises south of east and sets south of west - and by a significant margin.


Wal Bowles

2nd March 2004



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