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atoms and the sun


Pete Davis

on 23 February 2016

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Transcript of atoms and the sun

Atoms and the sun
At short distances the attractive nuclear force is stronger than the repulsive electrostatic force. As such, the main technical difficulty for fusion is getting the nuclei close enough to fuse.
Gold foil experiment
The sun is essentially a giant ball of gas and plasma that gets hotter and denser as you travel from the outer rim to the centre. Temperatures run from a mere 5780K on the outer visible layer (the photosphere) to about 15 MILLION Kelvin in the middle!
Coronal Mass Ejections
Coronal mass ejections occur when the confined solar atmosphere can suddenly and violently release bubbles or tongues of gas and magnetic fields. These result from a change in the magnetic field. If one of these coronal mass ejections erupts towards the earth it can effect electromagnetic equipment. Satellites are particularly vulnerable. However, the really exciting effect of a coronal mass ejection coming our way is the auroras that we see usually nearer the poles. In April 2000 a spectacularly big CME brought the aurora down as far as the south of England.

Pictures take at Hampshire Astronomy Group Observatory in April 2000 by Ninian Boyle
The Core
The core of the sun is the the real powerhouse. With temperatures at 15 million K and a density of 160,000 Kg/m3, this is the place where the nuclear fusion that generates massive amounts of energy takes place.
The Radiative Zone
Between the core and the convective zone, the radiative zone extends to about 70% of the sun's radius. The energy flowing from the core through the radiative zone, traveling in a very haphazard path, losing energy in the process.
The Convection Zone
The convection zone is a turbulent mass of material through which the radiation cannot pass as the temperature is too low (about 2 million K at the bottom of the convection zone). The energy pouring from the radiative zone gets trapped and cannot escape, so giant convection currents are set up with hot matter rising and the cooler matter sinking. This results in large bubbles of ionised gas rising through the convection zone, reaching the surface in about 10 days. It help to imagine a boiling pot of water with hot rising bubbles and cooler sinking material. The hot bubbles rise quickly to higher levels, cooling and expanding, just like hot air rising in the atmosphere of the earth. When it becomes cooler that its surroundings, the gas sinks to become reheated and rise again. In this way rolling currents of hot and cold gas create a churning motion that carries heat from the bottom to the top. It seems that largest currents of gas and heat generate myriad smaller ones and these manifest themselves as the granulation we can see in white light and H-Alpha.
The Photosphere
Sunlight as we know it - the visible white light, is emitted from the photosphere. The photosphere is one of the coolest regions of the Sun (about 6000 K), and it is here that we can see the granulation caused by the bubbling gas in the convection layer and the sunspots caused by strong magnetic fields.
The Chromosphere
The chromosphere is 2000-3000 km thick and the temperature rises from around 6000k to 20,000K. These high temperatures result in hydrogen emitting a reddish light (H-alpha emission) and can be seen in the exciting prominences that project from the sun and in the thin reddish line that can sometimes be seen as a 'rim' round the dark disk of the moon inside the corona. It is this colour that gives the chromosphere its name (color-sphere). The image to the left of a total solar eclipse demonstrates the colouring of the chromosphere. The chromosphere contains spikes of gas called spicules that rise through it. Spicules are short-lived phenomena, corresponding to rising jets of gas that move upward at about 30km/sec and last only about 10 minutes.
The Corona
This is the outer layer of the sun and is the whitish halo seen around the disc in a total solar eclipse. This can be seen in the picture of the solar eclipse above. Temperatures range from 2 to 3 million °.

The corona can exhibit coronal holes which can be seen in the spectacular x-ray image of the sun (right). It is from these 'holes' that a high velocity solar wind emanates. The wind consists of high speed particles streaming from the sun and can be viewed as an extension of the the corona into interplanetary space.
Atoms and the Sun
the Rutherford-Marsden-Geiger gold foil experiment
Nuclear Fusion
The structure of the Sun

Stage Fusion Products
Protostar none
Main sequence Helium
Red Giant Oxygen, Nitrogn, Carbon
Super Red Giant Elements up to mass of Iron
Supernova Elements more massive than Iron
White Dwarf none
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