How far is it to the sky?

Mrs B found this lovely book for me. It contains this page

Which begs the question: how far away is the sky? This led me to find out about the Karman line https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line Karman calculated the altitude at which an aircraft would not be able to travel fast enough to generate enough lift to support itself without travelling faster than the orbital speed for that altitude. So this is where the sky is said to end and space begins. It's arbitrary but I like that it is based on a calculation.
There was a new moon tonight just visible through the trees.

So

Midsummer Chronophage in Cambridge

This weird clock and another similar are star attractions in Cambridge. It took me a long time to work out how to read them. The outermost light races round in a second. I took repeat shots that show that the shutter is not always open for the same amount of time. One complete lap lasts a minute. The inner lights show that the time was roughly 20 to 5.

Another mathematical bridge

I have been past this bridge at Iffley Lock many times but hadn't realised that it is a replica of the Mathematical Bridge in Cambridge. The angled or horizontal long sections are tangents to the circular arc of the bridge. The almost vertical short posts are radii.

Knitted mathematics in Cambridge

Being someone who knits, I was amazed to find in the Whipple Museum of the History of Science these mathematical surface models knitted by a scientist over a century ago. There is more about them here: http://www.sites.hps.cam.ac.uk/whipple/explore/models/knittedinterpenetratingsurfaces/ It reminded me of when I was trying to make a model of a Riemann surface out of paper five years ago. http://wigtonphysics.blogspot.com/2015/01/trying-to-make-riemann-surface.html

Mathematical Bridge in Cambridge

I'd heard about this and also heard that there were myths about it, but now I understand it, I'm really impressed. The diagonal timbers are all tangents to the circular arc of the bridge and the upright posts are radii of the greater circle. https://en.wikipedia.org/wiki/Mathematical_Bridge I'm now on the hunt to find the replica near Oxford.

Josephson Junction

I also found this at the Cavendish Laboratories. I'd heard of Josephson Junctions but had never bothered to look it up. It turns out to be quantum tunnelling with superconductors, so that it is Cooper pairs of electrons that tunnel through the barrier. https://en.wikipedia.org/wiki/Josephson_effect

JJ Thomson and the electron

I was very pleased to visit the site of the old Cavendish Laboratories in Cambridge. It prompted me to look up JJ Thomson. https://en.wikipedia.org/wiki/J._J._Thomson He was experimenting with cathode rays. Following the chain back, it seems that the line of research started with the passing of big voltages through gases - an old-fashioned streetlight, in other words. Then they started to improve vacuums until they could remove all of the gas. They realised that they had a straight line ray. This is where Thomson came in. He was able to bend the rays with magnets and electric fields, to work out the charge-to-mass ratio. He realised that the particles were negative and smaller than an atom. The world of sub-atomic particles was born. I'm amazed by the number of Nobel laureates that he taught, including Wigton's own William Henry Bragg.