Moons of Jupiter

The run of clear skies with Jupiter prominent has convinced me finally to take an interest in the Galilean moons. One issue is that they won't photograph with my set up, so I went back old school and started to draw them. Nothing drawn for the 26th because I could only see two moons and thought perhaps the bright Full Moon was affecting visibility. Last night the penny finally dropped - sometimes when you look, the moons of Jupiter are in front of or behind Jupiter! Also I had been assuming that they were always at the extremes of their orbit as seen from Earth, but they might be part way round with our view seeing them shuttling backwards and forwards on an edgeways line view. This brilliant viewer has helped me to understand what I'm looking at. 

Weighing the wool

I needed to divide this ball of wool in half. The plan was to unwind until the two part balls weighed the same. Problem is that the balance won't register below 10 grams, though the resolution is +-1 gram.

The solution was to use an object heavier than 10 grams. That got it to register and the resolution was as good as needed.

Balloons in the cold

It was very cold on the morning of the bazaar. After the incident in September when sunlight on balloons put in so much energy that the balloons burst, I was interested to see what happened. This time, thermal energy should cross the system boundary into the surroundings, reducing the internal energy of the particles. For a gas, internal energy is the sum of the kinetic energies of the particles. The particles would have less kinetic energy so less frequent and softer collisions with the rubber and reduced pressure. That didn't happen. The balloons remained as they are pictured. However, the sun did start to shine on the balloons so that would put energy back into the system.

Fish tank ripple tank

The lighting in the cuttlefish tank at Maryport Aquarium was providing two sorts of ripple tank. Above, the light reflects from the ripples and is projected onto the ceiling. Below, it refracts through the surface and produces the pattern of light and dark lines on the sand.

Cearcall mun Ghealaich

I failed to see the aurora las night despite a red alert, but the halo around the Moon was magnificent. Lots of people saw it. This is the 22 degree halo. This means an angle of 22 degrees is subtended from the centre of the Moon to the halo. The Moon itself subtends about half a degree. I was hoping to make some measurements on the photo to verify it but even allowing for blurring of the Moon due to the overexposure needed to pick up the halo, I can't see it would work by measuring. Cearcall mun Ghealaich is a poem by Catriona Montgomery set and sung by Julie Fowlis about the portents associated with a ring around the Moon.

Silk Damping and dark matter

I have been listening to Sean Carroll's Mindscape podcast on the Crisis in Physics. I was put off at first because it is over 4 hours long but I have listened in installments. It's brilliant. I am learning so much and am going to try to explain to myself what I learned. He explains evidence for dark matter. One piece is from Silk Damping which comes under Diffusion Damping. This is how the differences in density in the early universe were smoothed out. Photons were released and free to travel. They interact with normal matter and took protons and electrons with them. This evened out the density but it oscillated until it settled down. If I have understood it correctly, it is damped by gravity. Here is a normal damping graph from mechanics with exponential decay in amplitude.

Here is the power spectrum from the Cosmic Microwave Background. The issue that Joseph Silk explained is why these two peaks have the same amplitude. The photons cannot interact with dark matter so the dark matter has no part in the outward expansion. However, on the rebound dark matter can exert a gravitational pull, making the peak bigger than expected. That's what I understood the podcast to be saying!

Burnt mince pie and 1st Law of Thermodynamics

 

Overdoing a mince pie in the microwave resulted in a cracked dish and a big burnt smell! It got me thinking about the treatment of the 1st Law of Thermodynamics at GCSE these days. Instead of just saying that work and heat can cross a system boundary, we now say it is mechanical work, electrical work, heating by particles and heating by radiation. If this pie had been in the oven at 180oC, it would not have been able for it to get higher than that temperature. The heat would be crossing the system boundary by conduction, ie heating by particle vibration. If the outside is at a higher temperature than the inside, then there is more energy transfer into the pie, but there will also be some coming out. At 180oC, the same amount would be coming in and coming out. Thermal equilibrium is reached. In the microwave, the it is heating by radiation that crosses the system boundary. As the pie heats up, there will then be some conduction (heating by particles) back out but this will be slower. So if a thermal equilibrium is reached it will be at a higher temperature. I suppose this neglects the idea that the hot pie itself is a black body emitting infra-red, but this clearly doesn't bring it to a sensible thermal equilibrium in the face of constant extra radiation heading inwards.