Image sun

The Sun

Our nearest star is the Sun. It is an enormous sphere of burning gasses, mostly hydrogen and minor quantities of helium. The sun’s radius is 700 thousand kilometres, about 109 times that of the Earth’s. However, as the figure shows, the Sun cannot be considered a very big star.

The small full circle on the left represents the Sun. Moving towards the right, the second circle represents the star Antares and it is about 27 times bigger than the Sun. On the right is the star Arcturus, which is about 400 times bigger than the Sun.

Despite this, the Sun’s mass, which is about 2 billion, billion, billion tonnes, corresponds to well over 99.9% of the total mass of the Solar System.

The Sun, like all stars, gives off energy in the form of light and heat. The energy is created because the gas particles in the sun’s core, squashed by the weight of its outer layers, are subjected to incredibly high pressure and temperatures. The temperatures reached are so high that the hydrogen particles are transformed into helium. This transformation is called nuclear fusion and it leads to a release of energy which once it reaches the sun’s surface, is emitted into space mainly in the form of electromagnetic radiation of various frequencies one of which is, of course, visible light.

All the other celestial bodies in the Solar System, including the planets, reflect some of the light given off by the Sun, and absorb some of it.

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