Leap year

The problem is that we measure time in rotations of this planet; in other words, we divide time up into days. Unfortunately, the rest of the Solar System is not organised in multiples of this scale division. Our passage around the Sun is roughly 365 1/4 days so to bring the calendar of days back in line with our passage around the Sun, we'd need to stick in 1/4 of a day every year. That's nonsense because it doesn't fit in with the way we live our lives so best to insert a whole extra day every 4 years. It seems that leap year days in February go all the way back to Julius Caesar.

Joseph Swan

I found this memorial to Joseph Swan in Newcastle. I remember hearing that he was actually ahead of Edison in inventing a light bulb. https://en.wikipedia.org/wiki/Joseph_Swan He initially used carbon filament - presumably meaning graphite, which conducts electricity. The problem is that it burns up. Swan managed a bulb that didn't have too much oxygen in it so it was able to get really hot without catching fire. The bulb is called incandescent because it becomes so hot that it glows.

Stopping the roof falling in at Bake Off

We went to see the snowdrops at Welford Park, home of the Great British Bake Off. I was windering about the S-shaped metal bits under the eaves of this building. Then I realised that it must be attached to a long metal pole that stretches through the building and out the other side. When you put a roof on a building, it has a tendency to sag downwards. That pushes the walls out. By Newton's 1st Law there needs to be an equal and opposite force to stop that happening. The S-shape spreads the force out over a bigger area and so reduces the pressure, stopping the bolt ripping through the brickwork.

Light is therefore colour - the new £20 note

The new £20 note once again features polymer made here in Wigton https://cclsecure.com/ccl-secure-to-again-supply-majority-of-polymer-substrate-for-new-20-note/ I was particularly taken with the quotation -  each different wavelength of the visible spectrum is perceived as a colour.

Corona through thin high cloud: looking at the Sun

Having seen the halo around the Moon, I became aware that I hadn't recognised a solar corona. This is caused by diffraction and not refraction. Since diffraction angle is linked to wavelength, the redder colour is on the outside. There is a great picture here https://www.atoptics.co.uk/droplets/corona.htm with an idea of what I need to do next time to improve my image. Also here https://www.weatherscapes.com/album.php?cat=optics&subcat=corona

The Alfred Jewel and Bertrand Russell

Given the camera and the lighting, it was impossible to get a good photograph but the details are here https://en.wikipedia.org/wiki/Alfred_Jewel The piece underneath it in the museum says that "it is thought to be a representation of the sense of sight". Is that possible? It reminded me of what Bertrand Russell says about light in The Problems of Philosophy. He says that when physicists tell us that light is a wave motion, that tells you little about what you experience. He says that if you put a person blind from birth onto a ship, you could get them to experience a wave motion, but that would not let them experience light. So a representation of the sense of sight is an amazing idea. https://www.sparknotes.com/philosophy/problems/section3/

Climate and the Nile

My new book on the physics of the climate says that the word "climate" originated with the ancient Greeks. Apparently they noticed that it got warmer as they went south down the Nile. They reasoned that they were getting nearer the Sun so they must be going uphill. Hence the word "climate" is based on their word for a slope. I enjoyed the ancient Egypt section in the Ashmolean.

Porcelain and the Arrow of Time

This installation at the Ashmolean Museum reminded me of the films I've seen showing a porcelain cup falling a breaking. You can tell when the film is being run backwards and this shows that time is not symmetrical. As the cup breaks, total entropy increases and this is one way of explaining why time is only one direction.

Reynold's number at the weir

This is the weir at Denton Holme. The flow at the top is laminar but it becomes turbulent lower down. The transition from laminar to turbulent occurs as the Reynold's number increases. Reynold's number is proportional to flow speed and the water accelerates under gravity. It appears to become fast enough to become turbulent very quickly.

Turning a corner on a river

I was wondering if I could use ideas from the flow of water round the bend in a river to explain some of the factors that produce gusts in wind. I had assumed that water flows faster round the outside of a bend because it has to move faster to keep up with the water on the inside. It's more complicated than that: https://en.wikipedia.org/wiki/Meander The Governing Physics section of the article explains the Secondary Flow. A thin layer of water touching the sand at the bottom of the stream has zero velocity but pressure still acts to move it inwards. The opposite happens above the surface so laterally there is a circulation, producing a sort of spiral effect as the general flow of water is along. This needs a lot more thinking about and still doesn't help me much with the gusts.

Why is the wind gusty?

With Storm Ciara in full swing, I was wondering about a question that I've never answered: why doesn't the wind blow at a steady speed? Why does it have gusts? The best short answer I've found is this: https://wxguys.ssec.wisc.edu/2012/01/09/what-causes-wind-gusts/ I suppose that it is no surprise that flowing round objects changes speed. There is variation when air flows over an aerofoil - the air goes faster over the top than the bottom to ensure flow rate remains constant. The same is true for flow round a swinging cricket ball. But I'm interested that they say it isn't gusty until the average speed reaches 18mph.

Procyon

Procyon is one of the Winter Triangle stars and is very obvious at the moment. It turns out that it is very close to us, just 11.5 light years. It is so bright because it is so close. It is a class F star so it is hotter than the Sun. It is a little bigger than the Sun and its intrinsic brightness is higher. In other words, our Sun doesn't look as bright from Procyon as Procyon looks to us. https://en.wikipedia.org/wiki/Procyon

Orion

Orion is prominent in the southern sky mid-evening at the moment. It's my favourite of the constellations. There's a lot to be said about the individual stars but today I've been drawn to an aid to finding other stars in the sky. I've come across the Summer Triangle but not the Winter Triangle https://en.wikipedia.org/wiki/Winter_Triangle. Even better, there is also a Winter Hexagon https://en.wikipedia.org/wiki/Winter_Hexagon. These also introduced a new word: asterism. It's like constellation, as in it is a pattern humans see in the stars, but is a more modern version that goes across the ancient constellation boundaries. The problem with Orion for me is that it is in the south and therefore in the direction of the bright lights of Wigton...

Andromeda

Since I can't take photographs of faint celestial objects, here's the nearest I can get to Andromeda, spotted on the way to Wallsend. I was so pleased when I realised that the light pollution in Wigton is low enough to be able to see the Andromeda Galaxy. Looking up the Andromeda Galaxy, I realise that I have half understood certain things. I had thought it smaller than the Milky Way but it is at least as big. Also that as the nearest galaxy, it was the first to suggest that it was so distant as to be outside the Milky Way, rather than just a cluster of stars within the Milky Way. https://en.wikipedia.org/wiki/Andromeda_Galaxy I'm working on an understanding of virial mass!

A halo around the Moon

There was a beautiful halo around the Moon on Saturday night. My camera is not good enough to capture it. This was an almost half moon that has saturated to look like a full moon. No chance of picking up the delicate halo. I measured with my hand and it was indeed a 22 degree halo. It is a refraction effect. https://en.wikipedia.org/wiki/22%C2%B0_halo

Aperture and starburst effects

Thanks to Emily for these pictures that show a starburst effect for headlights and streetlamps. There are more details here https://www.slrlounge.com/diffraction-aperture-and-starburst-effects/ which says that it is to do with diffraction. I was wondering how a circular hole could produce radial diffraction but then I remembered how variable apertures in cameras work. Scroll down on this link to see pictures of how it is done https://www.veedyou.com/gopro-low-light/ The aperture is not circular but a series of flat edges. Each pair of parallel flat edges acts as a slit for diffraction if the aperture is small enough. The first link shows that starburst only happens for small apertures. Emily's pictures suggest to me that this aperture must have 16 edges.