Darker in the mornings

 

My first day at work in 2014. It always seems darker going back after Christmas. I always though that it was just psychological after getting up in the light for a couple of weeks. In fact, if you look at the sunrise times, the sunrise gets later and later for a couple of weeks after the solstice. The days do lengthen because sunset time drifts out even more. The reasoning is to do with the tilt of the Earth and the fact that the Earth spins on its axis whilst also moving round the Sun. I'm working on a sensible explanation - maybe by next year!

How high is a plane?

 

This plane stood out today because of the length of its vapour trail. I'd noticed one the other day that stayed constant at about 3 plane lengths but this trail covered half the sky. I estimated that the plane itself blocked out perhaps 2 degrees of my vision when overhead. I'll think about how I can measure this more accurately. Two degrees is about 0.02 radians, where a whole circle, 360 degrees, comes out at 2pi radians. I know that I can calculate the height of the plane using the arc length formula, where angle in radians = length of plane/height above me. I estimate the length at 70m. This means that the plane was flying at 70/0.02 = 3500m or just over 2 miles up.

Not plugged in

The blue power light on my cable stays on for a while even when it's not plugged in. The computer will work on DC so the transformer will have a bridge rectifier in it. As well as the four diodes to make the current go one way only, there will be a smoothing capacitor to iron out the ac fluctuations. The light will stay on until the capacitor has discharged.

A Benchmark in Coniston

 

I've blogged about benchmarks before and here's one in Coniston. I can't find it on the benchmark spotters website but I did find it on the Ordnance Survey website. They reckon that there are about half a million of these left in the UK. Apparently this one is 50.823 metres above sea level. That's very precise. Think about how big a wave on the sea can be. You'd think that the nearest metre would be fine. But here the height is given to millimetre precision. Now mean sea level must be a construct but even so, with the continents moving and sea level shifting, that level of precision is potentially controversial. That said, if you don't measure to that level of precision perhaps it will be harder to detect changes in sea level or earth movements.

Getting reflection back to front

 

Here's an ambulance in Old Town, Swindon. AMBULANCE is written back-to-front on the bonnet so that it can be read in car mirrors. The way that mirrors flip things back-to-front is called lateral inversion. So how come they don't put the writing upside down? That's because rays that are travelling horizontally into the mirror are reflected back horizontally. The top ray and the bottom ray can't cross over as they would for a less or for a concave mirror. In fact, lateral inversion is not caused by the left and right rays crossing over either. It's basically an optical illusion. If you look at your reflection in the mirror, it has to be a reflection of the front of you. The rays can't cross over left and right, so the ray on your left will come from what would be the right hand of your reflection.

Spring tide for the New Moon

 

This was high tide in Dumfriesshire this lunchtime. It is the New Moon. The Moon is lined up with the Sun on the same side of the Earth. They are both pulling on the water. The Sun is a lot heavier but a lot further away. This, coupled with high onshore winds, meant that the sea was almost onto the dunes. The relative pull of each heavenly body is proportional to its mass divided by the distance away squared. For the Moon, this is 7x10^22/(3.8x10^8)^2 = 4.8x10^5. For the Sun it is 2x10^30/(150x10^9)^2 = 8.8x10^7. The pull of the Sun is actually about 180x bigger than the Moon. However, it is not this that affects the tides. It is the difference of pull from one side of the Earth to another. That's going to need further calculation.

Ringing out the old, ringing in the new

 

HAPPY NEW YEAR!

 

Last night we rang in the New Year. We rang out the old before midnight. That was done with the bells half-muffled to give a more mournful sound. It's done by strapping a piece of leather to one side of the bell clapper, as shown in the picture. The leather is a more springy material that the metal. It deforms slightly when it hits the side of the bell. This makes the collision last slightly longer. The same change in momentum taking place over a longer time means that less force is involved. This doesn't get the metal vibrating as much as a direct hit with a metal clapper.

 

Just before midnight we took the muffles off so that we could ring in the new with a full peal of loud bells.