Enchantment and Brocken Spectres

 In her book Enchantment page 177, Katherine May makes the devastatingly simple point that the glory is round the head of the observer because it is the eyes that see and line up the anti-solar point. So no glories round my knees because no eyes to see it there! It's an obvious point but one that I'd missed. 

Enchantment and tides

I've been liking the very visceral way in which Katherine May writes about experiencing gravity. On page 94, she uses an explanation about why there are two tidal bulges that mat be helpful to me. I have never quite managed to understand the physics of tidal forces. She says that the bulge furthest from the Moon is because the force of attraction is weakest there and without a strong attraction the water is not pulled down but piles up. I need to think about that: weaker pull makes for deeper water.

St Ninian's tombolo beach: refraction or diffraction?

 

I thought tombolo beaches were due to diffraction round an object. It turns out that this includes refraction. The ends of the waves closest to the island slow down in the shallower water near the island by refraction. This changes the direction of the wave so they bend inwards on both sides and meet behind the island. The slower water is able to pick up sediment which is then deposited to form the tombolo beach.

Hybrid power ship

 

We spotted this in Aberdeen harbour. It turns out that a hybrid power ship is one that runs on diesel but also has a large storage battery system. Despite having looked it up, I don't fully understand the charging of the batteries. It seems that battery power is used in low power situations (this might well mean low speed) such as going in and out of port. Perhaps the diesel is run at a flat rate and any surplus goes to the batteries. They are claiming various advantages.

Lateral inversion on holiday

 

I was asked to explain why the writing we could see back-to-front inside the coach ended up the right way round in the reflection. The reflection point is just an axis of symmetry. Bits nearer that axis will also appear near the axis when reflected. Bits further will appear further in reflection. The net effect is the put the letters back to front. In this case, that actually made them readable!

Low energy light payback

We were excited to find dimmable GU10 LED bulbs. These ceiling lights had seemed like a good idea 20 years ago!

The new bulbs were roughly £2 each. How long might the payback time be? The old bulbs use 46.4W more. 1 kWh costs about 30p at the moment. So £2/30p = 7 kWh to 1sf. 7kWh/46.4W = 150 hours roughly. So that would be one year of half an hour a day and we will be in profit.

Northern Lights

Lerwick would be a great place to see the Northern Lights but clearly not on a sunny summer afternoon. The hare will have to do! I looked up the source of the different colours. The green comes from electron jumps between energy levels in atomic oxygen. I have to think about that. Not molecular O2 but high enough up in the atmosphere for the bonds holding the molecules together to be broken by high energy radiation from space and individual oxygen atoms to be loose. The blues and purples come from molecular nitrogen lower down. Maybe one day I'll be lucky enough to see it for myself.

Map distance measurer tool

This old-fashioned map distance measuring tool is a gem. It uses the fact that the same angular displacement produces a different linear displacement. The linear displacement is proportional to the radial distance.

I read the radial distances as 6mm, 8.5mm, 10.75mm, 12.5mm. The ratios almost work. 5/4 = 1.25 but 12.5/10.75 = 1.16. 4/3 = 1.33 but 10.75/8.5 = 1.26. 3/2 = 1.5 but 8.5/6 = 1.41.

Thinking about fountains outside Marischal College

The fountains outside Marischal College were fascinating. I was trying to photograph the falling drops to show that the gaps between them increase as they fall, like the strobe work I used to do in the labs. What I noticed in the picture is that there are big blobs of water at the top. I didn't watch the fountains carefully when I was there but I guess that means that the fountains are pulsed and that it fires up one shot of water followed by a pause. The individual drops must be what happens as the flow is cut off.

Wind Farm off Aberdeen

I like looking up details about wind farms but this one beats most. It is small but seems to be a test and demonstration facility and is one that caused a famous objection. It then led me to find out about suction bucket caissons as a way of anchoring the wind turbines to the sea floor. Sounds like you push the bucket into the marine floor sediment and suck some water out to reduce the pressure. Then the higher water pressure outside would pin the bucket to the sea floor.

Electric bus charging

I spotted this bus charging at Union Square in Aberdeen. I looked up some details. Here is the press release. I then looked up the bus type and found the manufacturer's website. Then I found this data sheet. If the battery is 472kWh and we take then 2x40kW AC charging option, that suggests a full recharge time of about 6 hours. I wonder if they do full recharge overnight and top up during the day.

Learning about the Milky Way

I have been given a paper to read about the Milky Way so I'm having to learn a lot of new vocabulary. I hadn't come across the thin disk and the thick disk as structures within the Milky Way. I had read that thick disk stars contain less metal. I guessed that meant they were older and it looks like that is correct. 

Electric car fire blanket!

We were intrigued to see this on the Bressay ferry. Looking up the idea of electric car fires, I found this. They say that these are chemical fires that "don't need oxygen". I think that means that they don't need oxygen from the air because there are oxidising agents in the battery that provide the oxygen. They talk of containment but not about being able to put the fire out completely. You'd think the sea water around a ferry would help but that can't be used because it would lead to a release of chlorine.

Bressay: burnt mound update

I posted about burnt mounds after our first trip to Shetland. This time, we found an amazingly complete excavated and rescued burnt mound by the ferry on Bressay.

Rocks were heated in the furthest chamber.

The hot rocks were transported forwards and put into this water tank at the front. The tank looks to be 1m wide by 2m long by 30cm deep. That makes 0.6 cubic metres or 600kg of water. I was talking about heating 5kg. This is over a 100x smaller. So we would be talking about maybe 300kg of rock, or 100 large pebbles, to get the heating to 60 oC.

Looking for Hawaiite on Canna

 The exposed bedrock on the top of Compass Hill was very friable. This sample dislodged under me!

The BGS viewer tells me it is Hawaiite but that it is aphyritic. I had to look that up. It means that it doesn't have phenocrysts - crystals that are obviously much larger than the other grains. I can see some much larger bits in this rock. It probably means that they don't count as phenocrysts. See here for Hawaiite from Rum. Here for details of what Hawaiite is.

Scattering: Fair Isle at sunset

It was amazing to line up the sunset with Fair Isle from the ferry. In fact, the sun set 3 times: it disappeared then the relative movement of boat and sun lined up the very top of the sun with a lower gap on the island so it could disappear again!

Focusing on the droplets on the outside of the window gave a lovely example of scattering. Light from the sun hits the droplets and then is re-emitted to my eye. This is like what happens with the atoms in the high atmosphere. Rays of light from the sun that are not coming in my direction are absorbed and then re-emitted back in my direction.

Light sensor on water bottle filler

I was having trouble with the bottle refiller in the ferry terminal in Lerwick. Then I noticed the black dot at the bottom of the blue bottle graphic. Turns out it must be a light sensor which activates the water flow when it is dark enough. My bottle was completely clear so it wasn't blocking the light. Putting my hand around the bottle rectified the problem. I wonder what happens at night?

Data centre power use

I saw this article a few weeks back about data centres using up 18% of Ireland's electricity. I have been after figures about this sort of thing for a while and have now discovered this brilliant book by Mike Berners-Lee. He calculates that data centres use 1% of the world's electricity with countries that host many centres for tax reasons having a far higher percentage of their electricity used.

Wind power on a narrow boat

I saw this boat in Oxford. I was wondering what the power rating of a turbine like this would be. I found this site. It sounds like 130W. They do have data to back up what they are saying. I am wondering whether they mean Amp-hours Ah rather than Amps per hour because battery storage is measured that way. I found this to look at 

https://www.drivingelectric.com/your-questions-answered/325/what-are-kwh-and-ah

Robert Hooke

I haven't really ever taken much notice of Robert Hooke. Hooke's Law always seemed trivial and obvious. Newton's work is seen as so vast and foundational. I hadn't realised that Hooke had studied at Oxford. With Newton at Cambridge, there's another potential cause for rivalry. He does seem to have been involved in a lot of fields.