- The Sun gives life to the Earth and the Earth would have no life at all without the energy it receives from the Sun.
- The Sun is only one of millions and millions of stars in the Galaxy.
- We see it as a large round red ball only because we are much closer to the Sun than to any of the other stars.
- Other stars may be larger, brighter, smaller or fainter than our Sun but they are so very far away that we only see them as points of light in the night sky.
- The Earth is one of nine planets that orbit round the Sun in what we call the Solar System.
- Solar is the adjective from Sun and comes from the Latin word for Sun – sol, which also gives us the French soleil. (and the word for Sun in several mother European languages).
- The Sun measures 2,715,395 miles (4.730,005 kilometres) right round (diameter).
- The Sun is 92.96 million miles or 149.6 million kilometres from the Earth.
- The Sun is bigger than can really be imagined, over one million times bigger than the Earth.
- This measurement is taken as one Astronomical Unit and is how we measure distances in our Solar System
- Like all stars, the Sun is composed of a great burning ball of gases. It is made of 92.1% hydrogen and 7.8% helium (helium is from the ancient Greek word helios, which means Sun).
Figure 1. The burning heat of the Sun
- The Sun has six layers.
- The centre of the Sun is its core which produces all the Sun’s energy.
- Around the core is the radiative zone, which carries the energy out from the core.
- It takes about 170,000 years for the Sun’s energy to move from the core through the radiative zone to the next layer, the connective zone.
- From the connective zone, great bubbles move into the Sun’s surface, the photosphere.
- From the photosphere the Sun’s radiation escapes to the earth as sunlight.
- It takes about 8 minutes for the sunlight to be seen on the earth after it has left the Sun.
- Outside the Sun’s surface, or photosphere, are two further layers of light gases, the chromosphere and the corona (Corona means “crown” in Latin).
- These are too faint to be normally seen against the much brighter photosphere but they can be seen on a very dull day or during a solar eclipse (Look at figures 2 and 3.).
- In very bright weather it is dangerous to look directly at the Sun without protective glasses.
- On a dull day when the sky is overcast, you can often see the Sun’s corona – the bright layer around the Sun’s photosphere.
- As the moon orbits round the earth, it very occasionally comes between the Sun and the earth.
- This shuts out most of the light of the Sun and is called a solar eclipse. Sometimes only part of the moon comes between us and the Sun: this is called a partial solar eclipse.
- In a total solar eclipse it is often possible to see chromosphere, the layer of thin gas between the Sun’s surface and the Sun’s corona. You may be able to see the chromosphere as a thin red line in Figure 3 with the corona outside it.
Figure 2 The Sun's corona - the hazy bright area around the Sun, seen on an overcast day.
Figure 3. The moon has eclipsed the Sun which cannot be seen. Only the chromosphere and corona of the Sun can be seen.
- Sometimes darker spots are seen on the surface of the Sun. These are magnetic areas which are cooler than the rest of the Sun. They are called Sunspots.
- Many civilisations, such as the Aztec civilisation in Mexico, have worshipped the Sun.
- Many prehistoric stone circles, such as Stonehenge, are thought to have been built as part of religious worship involving the Sun.
- In the past many people believed that the Earth did not move and that the Sun rotated round the Earth.
- The first scientist to suggest that the Earth and other planets moved round a fixed Sun was Aristarchus of Samos (310-230 B.C.) – more than 2000 years ago.
- The scientist Ptolemy, however, writing more than 300 years later, in 140 A.D. said that the Earth was the centre of the universe. This was believed for another 1400 years.
- The great Polish scientist Nicholas Copernicus (1473-1543) published a book at the end of his life, in 1543, in which he tried to prove that the planets orbited round the Sun; the book’s title was De Revolutionibus Orbium Coelestium (Concerning the revolution of the heavenly spheres).
- Those people who agreed with Copernicus were often imprisoned and even executed for suggesting that the earth moved round the Sun.
- The work of the Italian Galileo (1564-1642) and the German Johann Kepler (1571-1630) reinforced Copernicus’ theory.
- The theory of the Solar System was not really fully accepted until the great English scientist Isaac Newton (1642-1727) published his works on the theory of gravity and finally proved that the planets orbited around the Sun.
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