The Sun is not only the largest body in the solar system it is also the most important. For without its influence, the planets could not be held within the solar system and there would be absolutely no chance of life ever developing on the Earth.
The Sun is our star and is about 4.6 billion years old. Although it looks spectacular in the sky above us, it is at best an average star in many ways. It is not one of the largest or smallest of stars. It’s also not among the hottest or coolest. In fact it is quite ordinary within the trillions of stars that we know exist in the universe. Astronomers classify our Sun as a yellow dwarf star.
All this does not mean that our Sun is not still an amazing object. It is 864,900 miles in diameter which makes it over 109 times greater than the Earth’s diameter. Light and other forms of energy take approximately 9 minutes to reach us. Since this energy travels at the speed of light, we can calculate that the Sun is about 93 million miles away.
The Sun is a huge gaseous ball of energy consisting of about 73% hydrogen, 25% helium and various other heavier elements in small amounts. Within the core of the Sun, the hydrogen comes under great pressure and heat. So high are they that the hydrogen atoms are fused together to form helium. This process called fusion also results in the release of large amounts of energy in the form of heat and light.
The rate at which it does all this is amazing; over 600 million tons per second and of this, over 5 million tons is in the form of energy. This energy then rises to the surface by means of radiation and convection systems.
The surface of the Sun is called the photosphere and it may surprise you to learn that the surface is cooler than you might imagine. It is still hot but at 5,500º Celsius it is within our understanding. However, as you move deeper into the Sun the temperature rises. At the core where the nuclear fusion takes place, it rises to a staggering 15 million degrees.
At this point it must be stressed that you never look directly at the sun. If you do, your eyes will be damaged. There are safe methods of observing the Sun and you must study them before you attempt it.
The photosphere is about 300 miles thick and if you were to study it, it would take on the appearance of an orange because the surface is mottled like the peel of an orange. The reason it appears this way is because there are cells of rising gas breaking through the surface all the time. In addition there are many jets of gas escaping which help maintain this appearance.
From time to time, dark patches also appear on the surface. These are called sunspots and they indicate where the surface is slightly cooler. When we say cooler, it is all relative as these areas are still about 1,500º Celsius. Closer examination shows them to be composed of two distinct components. There is a dark centre called the umbra and this is surrounded by a lighter area called the penumbra. The umbra is the coolest part of the sunspot. Sunspots appear in cycles of about 11 years. They occur because some of the rising hot gases do not make it to the surface.
One of the most amazing aspects of the Sun’s activity is when it ejects a solar flare. The cloud of gases making up a solar flare can be massive and last for many hours. Another type of eruption takes the form of a solar prominence. These are also made up of a cloud of erupting gaseous material but they can stretch out much further into space and last for much longer.
The sun is the reason our solar system is held together and why the Earth can support life. But we are not alone and in future articles, we shall discuss the planets and other objects in our solar system.
John Pullen 