The Sun
The Sun is a G type main sequence star which formed about four and a half billion years ago when a cloud of hydrogen collapsed. The Sun is about halfway through its life as a main sequence star and in about five billion years time it will become a red giant. It is just over one hundred times as wide as the Earth and over three hundred thousand times as massive, accounting for over ninety nine percent of the total mass of the Solar System.
The Sun is described as a plasma, a state of matter similar to an extremely dense, partially ionised gas. It has a temperature of over five and a half thousand degrees Celsius and is mostly composed of hydrogen, with some helium and trace elements of oxygen, carbon, neon and iron.
The Sun rotates faster at its equator than its poles and this can lead to 'twists' in the magnetic force which is created by highly ionised iron and oxygen in the atmosphere. When this force is strong enough it can cool the surface, darkening it and creating tiny pores called granules. Granules may last for just a few hours and disappear, but sometimes they grow as more magnetic fields are brought to the surface. When a pore is a few thousand kilometres wide it is referred to as a sunspot. Singular sunspots are soon accompanied by others and a group forms. Groups travel around the Sun about four times before the field is destroyed and they disappear.
The Star Garden
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The pressure in agitated magnetic fields can get so high that a dense cloud of plasma is emitted from the surface in a Solar flare. Photons are pushed into the photosphere creating a bright flash, which is hotter than the centre of the Sun, and a thousand billion tonnes of matter, including electrons, ultra violet light and x-rays, fly out towards the Earth. Minutes to hours later, a stream of Solar cosmic rays are emitted, these are mostly composed of protons travelling at over ninety nine percent the speed of light. Solar winds that can reach further than Pluto, creating a 'bubble' around the Solar System.
When charged particles enter the Earth's magnetosphere they follow the magnetic field lines to the poles, ionising atoms in the upper atmosphere and creating aurora, the northern and southern lights.
References
See NASA's profiles of the Sun.