An interesting statement about ultrasound

 I bought a new ultrasonic scarer for mice. It is interesting to note that cats and dogs can hear some ultrasound but that this is pitched too high for them.

Most physics teachers would be aghast at that the statement that "ultrasonic waves behave in a similar way to light": hey! Ultrasound is a longitudinal wave and light is transverse - it's  a bad source of exam confusion. But hold on! Actually, the point being made here is that ultrasound will not travel through objects either. Given its use in pregnancy scans, it would be understandable if people thought it was. You need saline gel to get the ultrasound to go into a body and that only works because the speed of sound in saline gel is the same as in muscle. Even saline gel would probably not get ultrasound into furniture - and it would be messy....

Apparent brightness: Wigton lights

 

The Wigton lights have been lovely this year. There were stars hanging from the strings across the street. These were all identical stars but illustrate one point about the brightness of the stars we see in the sky. Here in Wigton we can see the distances between these stars but we can't tell when we look into the night sky. Everyone understands instinctively that if something is further away but intrinsically the same, it will appear to be dimmer to the observer. It follows an inverse square law: doubling the distance means there is a surface 4 times as big over which to spread the light energy. The brightness is therefore reduced to 1/4 of what it was.

Vesta V47 turbine at Watchtree

Watchtree have placed the old generator from a turbine on display. It prompted me to go looking for information on the turbines. I started here. I found that they are quite old turbines made in Denmark called Vesta V47. Each one can generate 660kW. Even better was the information on the turbine type. I always love a graph and if you scroll down it shows what to expect for each wind speed. Translating into miles per hour, it needs 9mph to get generating, hits full power at 33mph and shuts down at 56mph. The turbine forecast for tomorrow is 68% which I assume means 68% of 660kW = 450kW. From the graph that means wind speed of 10m/s which is 22mph. The BBC forecast for Wigton is for 16mph tomorrow. Watchtree is exposed so the prediction is not unrealistic but it has to be really windy to generate full power.
 

A mystery solved : Langmuir circulation

 It's taken 5 years but I have finally found the answer to a question I raised in a previous post. I've been reading John Muir's book First Summer in the Sierra and he mentions seeing what he calls "windrows" on a lake. These lines of foam turn out to be what I've seen on lakes too. They are odd because whilst wavefronts form perpendicular to wind direction, these windrows form parallel to wind direction and I couldn't see a mechanism to do this. Turns out it is called Langmuir circulation. Now I need to work out how the wind makes these vortices under the surface of the water.

Winter high pressure causes renewable energy crisis

 

The notice at Watchtree said that the solar powered card reader wasn't working. This has been a UK-wide problem in the second half of December because an area of high pressure settled in but gave cloudy skies instead of the clear blue skies often associated with a high. So solar electricity was severely reduced at the same time that very light winds reduced wind power to almost zero. Diversity of sources will help us to cope. But as we make cash in Wigton, there was still the option to donate that way.

Vacuum fluctuations at Farmoor

 It was a very calm day at Farmoor Reservoir.

We did spot the Great Northern Diver.

It occurred to me that even on a calm day the surface of the water is not perfectly still. Looked at closely, small ripples are visible. This reminded me of the amazing discovery that a vacuum is not a smooth emptiness but is a seething mass of virtual particle pairs popping into and out of existence due to energy fluctuations based on Heisenberg's Uncertainty Principle. https://en.wikipedia.org/wiki/Quantum_fluctuation

How I missed Comet Leonard

 

I have started looking at APOD again after over a year away and found that there has been a comet around this last year https://apod.nasa.gov/apod/ap211227.html Unfortunately it seems that it has now become a southern hemisphere object https://www.skyatnightmagazine.com/advice/comet-c-2021-a1-leonard/ It shows that I need to resolve to pay more attention this year!