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.