Late sunrise in the Cotswolds

Sunrise has been getting a little bit later every morning since the solstice although the hours of daylight have been increasing. Things are complicated by the way that the Earth has two cycles of motion. It spins on its axis but at the same time it moves around the Sun. This means that it has to rotate through 361 degrees to get to the point where the Sun is the same height in the sky. Also the Earth follows an elliptical orbit around the Sun. At the moment the Earth is closer to the Sun than at other times of the year (see diagram on http://www.jwstelly.org/TheCalendar/Gregoria nCalendar.html According to http://www.bbc.co.uk/news/magazine-30549149 this means that one rotation of the Earth lasts 24 hours and 30 seconds at the moment. I think I'll need to draw some diagrams to get to the bottom of this. And that's before you chuck in the tilt of the Earth. But the darkest morning will be Jan 2nd and then it gets better.

Hot and cold in Tewkesbury Abbet

 Tewkesbury Abbey is heated by two amazing boilers. Each is surrounded by fins to increase the surface area because they give off infra-red thermal radiation. As such they are painted matt black to be the best emitters.

I also found this max-min thermometer. It's so old that it is marked in Fahrenheit only. It looks like a proper mercury thermometer. It doesn't look to have been reset for a long time. Translated into Celsius, the minimum is about 6 Celsius and the maximum 20 Celsius. That's a bigger range than perhaps I expected. The thermometer is on the opposite side of the nave to the heaters so there must have been a period of sustained hot weather.

Warhol reminds me of quarks

The three versions of the same painting by Warhol in three different colours reminded me that charge for the strong interaction comes in three types. Electromagnetic forces have two types of charge and these are called + and -. But there are three quarks needed to make a baryon and three together would add up to zero. The idea for colour charge came from the way that red, green and blue add up to make white in the primary colour definition. So the three quarks in a baryon would be assigned red, green and blue charges to make that baryon colourless.

Warhol: high contrast

I found this painting in the Andy Warhol exhibition at the Whitworth Gallery in Manchester. I have been teaching about contrast media used in medical physics. X-rays are attenuated by high density materials, dependent on atomic number. Calcium is especially good at attenuating X-rays so bones block X-rays but soft tissue containing water, mainly hydrogen and oxygen, mostly let X-rays through. There is a big contrast between the two media and you get a clear image of the bones. X-rays of organ systems like the digestive system fare less well because the muscles attenuate as badly as the contents. So patients are given a barium meal which occupies the space inside the bowels which attenuates a lot so giving high contrast with the muscle walls, The barium meal is called  a contrast medium.

Series circuit in Manchester

I liked these Christmas lights in Manchester. Traditionally, tree lights were wired in series so that there was only one way round the circuit for the current to flow. Hence if one bulb blew, it turned off the current so that all bulbs went out. Then you spent Christmas testing every bulb individually to find out which one had actually blown. These must surely be wired in parallel!

Measuring the remains of the balloon

Last month I did some calculations based on my birthday balloon. http://wigtonphysics.blogspot.co.uk/2016/11/finishing-birthday-balloon-calculations.html The balloon has now been laid to rest and I took some measurements. I was wrong about the mass of the balloon. At 10.34 grams it is less than half of my estimate. Also the thickness turned out to be twice my estimate and exactly what the Internet told me it should be. So  my estimate of dimensions must have been wrong!

Great Slab on Bowfell: ancient caldera lake

Great Slab on Bowfell was one of my great days out this year. I had been thinking about a post about coordinates on an inclined plane. But then I found out why it is so flat: volcanic ash settling in water in an ancient caldera lake. This time last year I was in a modern caldera. And the evidence as to why it was a freshwater lake is given on http://www.ronaldturnbull.co.uk/pics/geopix/Pages/17.html