Astronomy Lesson

The attached image was taken in the Rub Al Khali, Oman several years ago. To be precise on 21 January 2009 at 0332. The exposure was approximately 40 minutes. The duration of the exposure was dictated, not by the exposure meter or my guesstimation of correct time, but by the length of time the camera battery lasted!! The camera was set up in the Bedouin tent we were sleeping in. Mark, my expedition mate slept blissfully right beside me throughout the exposure. You can see the roof of the Bedouin tent at the top and the nearby sand dunes at the bottom.
So why am I suddenly here telling you all this after two years? Well, if you look closely at the star trails you will notice there are two circular patterns - one to the left and one to the right. I never noticed this until the end of the expedition. We were perplexed, but figured it had something to do with the equator.
Just last month, Mark was back in UK doing a celestial navigation course down at Arundel. He showed this image to his tutor and here is his response......

"This is a great picture. This is what I can work out:
It was taken looking approximately 15 degrees south of west, i.e. 225 degrees. I could work it out precisely but it would take a few minutes. It was not taken on the 7th, 8th or 9th January (moon would be in picture).
We can see Orion's Belt just above the horizon one third the way in from the right of the picture. The brightest star, near the middle of the picture, is Sirius, the brightest star in the night sky. The two bright stars near the top right are Pollux and Castor, the heads of the Gemini Twins. Between Sirius and Gemini, there is Procyon, which is another star we can use to find the celestial equator (go from the fainter star to its right of Propyon, on to Propyon then carry on double that distance).
The curves are caused because we are indeed looking at both the northern and southern halves of the celestial sphere simultaneously. All the stars to the right of Orion are wheeling anticlockwise about Polaris which is a long way to the right of the picture. All the stars to the left of Orion are wheeling clockwise about the south celestial pole, which would be well to the left of this picture and 18 degrees 'underground'. We are seeing the outermost stars of the great 'wheels' that turn about each celestial pole, hence the gentle curves".

I was gobsmacked at this awesome answer. I just had to share it with you. I do have some friends who are keen amateur astronomers who would be interested in this.
So there you have it - a lesson in astronomy.
Thanks Mark for forwarding the information on to me. I look forward to my next lesson in the desert!!