Convex and concave mirror at Dundraw

This broken mirror at Dundraw shows both concave and convex reflections. It should be convex and the image is the right way up in that one. The sky is at the top. The broken bit is now concave and from a long distance beyond the focal point, the image is inverted - the sky is at the bottom. Below is the concave part from close up where the image is the right way up again. I must have been closer than the focal point.

Medium and high power electric car chargers

We were intrigued by the sign at Scotch Corner services.

The box by Medium Power said 125A at 400V which is 50kW

Gridserve's website gives High Power at 350kW so should charge 7x faster. 

o

Prime numbers in the park

 

I was wondering about the choice of numbers on the steps up to the slide; then I realised they were prime numbers. I decided to look up the uses of prime numbers. This site explains well the use of prime numbers in encryption, saying that the use of very large prime numbers just means that at the moment the decryption problem is just that it takes so long for even a super computer to work out all the possibilities. This site explains the cicada life cycle issue very well.

The Great Square of Pegasus

 

This is another asterism that is visible in the eastern sky after dark at the moment. Alpha has apparent magnitude 2.48, beta is 2.42 and gamma is 2.78 so they are well matched. The other corner actually belongs to the constellation Andromeda. They are all named in Arabic. My book says that a good test for visibility is to count the number of visible stars inside the square, with a dozen being a good number. Looks like the camera was doing well that night. The reflection of the orange street light on the telegraph pole has come out well.

Volt-amps and my bathroom light transformers

 

I need transformers to get the bathroom lights down to 12V for safety in a wet environment. I notice that whilst the power of the bulbs is measured in Watts, the power of the transformer is measured in VA or volt-amperes. The issue is that the transformer contains inductance coils. With AC, they become electromagnets whose polarity is constantly changing. This means a rate of change of flux inside the coil which generates an emf by Faraday's Law. By Lenz's Law, it must be a back emf to oppose the motion that caused it. In other words, it effectively reduces the flow of current as a resistance would do. It is not resistance because it is not that mechanism so we call it reactance instead. It puts the voltage  out of phase with the current. This means straight volts x amps = watts doesn't work here. Using VA makes that distinction.

Water cycle x2

The park in Penrith probably has the best view of any in the UK. We liked the board explaining the water cycle and marvelled that we could see it happening in front of our eyes. Heavy showers followed by evaporation on a warm summer afternoon. 

Asterisms

 

Until very recently, I thought that the patterns in the sky were called constellations. However, the word I keep coming across this week is "asterism". There are patterns that we see in the stars that are not constellations. One such is the Summer Triangle. Sadly, my picture only has two of the three stars in it! Another example would be the Plough which is only part of the constellation Ursa Major. So asterism is a more general term that includes constellations but also other patterns.

Diffuse and specular reflection

Between showers at Watchtree there were excellent examples of diffuse and specular reflection. Diffuse is from a rough surface when light is thrown in many directions. What you see is just brightness, as the tarmac surface shows. Specular reflection is when the rays all emerge parallel to each other from a smooth surface and so you see a coherent image. I could see the clouds reflected in the puddle. The relevant ray diagrams are on this site.

Cygnus X-1

 

I was aware of Cygnus X-1 in my teenage years because of Rush's songs based on it, but at that point I had no idea what a black hole was. By the time I'd started teaching about black holes, I'd forgotten about Cygnus X-1. So belatedly I have found out where it is in the sky, although I have no equipment for seeing it. It is X instead of a Greek letter because it is an X-ray source. It turns out to be the object about which Kip Thorne and Stephen Hawking had their bet, Thorne winning when it was settled on as the first observed black hole. 

Apparent magnitudes in Cygnus

 

I was wondering how dim a star I could see with my phone camera on an 8 second exposure. I looked up the apparent magnitudes here. Looks like the dimmest stars visible are eta and o2 which are magnitude 4. The Moon was up so that might have had an effect.

Thinking about Shell Stars

 

I looked up Cassiopeia in my book. Gamma Cassiopeiae was the main attraction and the book calls it a "shell star". However, the star gets its own Wikipedia page which does list some features of a shell star, such as very rapid spinning, but calls it an "eruptive variable". It is also the first Be star discovered. I am familiar with the idea of rapid spin producing broader spectral lines because of Doppler Shift but there is a lot more in here to digest!

The Moon and Jupiter

 

Inspired by yesterday's APOD, here's my attempt at the Moon and Jupiter taken from High Pike. Sadly my over-exposed image doesn't show that we are half moon at the moment. Jupiter is to the right and you can just see the red of Skelton masts.

Didn't get to find serpentine!

 We made it as far as the top of Yell only to find out that there were no boats to Unst. I had been hoping to find rocks from the Shetland Ophiolite Complex there. Here's the view from the ferry port towards Unst.

I found this rock in the museum at Scalloway.

The rock below came from the end of the pier at Gutcher on Yell. You could see the ophiolite rocks across the water. There were superficial similarities - I was optimistic.

Unfortunately closer examination suggests that it is a type of schist - layers of crystals. It was not bedrock so it could have come from anywhere in the vicinity - but probably not Unst!!

Kinematics in the Milky Way

I have found out that one way of sorting out the stars in the Milky Way is by stellar kinematics. It seems that older stars move faster than younger stars. I have been told that when stars approach each other, slingshot from gravity tends to make them depart faster. The older they are, the more such encounters they will have had and thus the faster they go.

Hawking Radiation!

The cinema at Workington has a small section called the Hawking Room. The lit-up sign made me think of Hawking Radiation. I had always understood this to be due to pairs of virtual particles being created near the event horizon and then one falling into the black hole before they annihilate again - the spared particle being the radiation. It turns out it's not quite that but that my idea is an approximation. It's an idea called the Unruh Effect that means that such particles appear to an accelerating observer.

Air source heat pump for the Saxons

The wonderful Saxon church in Wareham had a sign outside about the installation of heat pumps. I was enthusiastic about heat pumps after reading David Mackay's book over a decade ago at the start of this blog. Some of the practical problems are now coming to the surface. There was a great BBC article this week that points out the cost of retro-fitting installation and who will pay for that. Also that if you already have radiators, they will have to be replaced with bigger ones. When the Ukraine war started and the fossil fuel prices jumped, we thought heat pump owners would have low bills. The trouble is that electricity is needed to run the pumps and the electricity prices jumped with the fossil fuel prices. 

Full Moon Cake

Full Moon today so I tried to recreate the face of the moon on a cake.