The Sun


Our small part of the universe is bound by the gravitational pull of our sun. At the moment we know there are eight planets (there may be more that we haven't discovered yet), three dwarf planets, two belts of asteroids, and other smaller particles and bits and pieces in our 'neighbourhood'.

We think of this collection of objects as a system, the solar (sun) system.

The sun

It is hard to believe that the sun is just a star, similar to those we see in the night sky. It is a ball of very hot gas. The main difference is that the sun is much closer to Earth than all the other stars we see. It is only 150 million kilometres from the Earth. This may still seem like a very long way away, but it is close enough to provide the Earth with sunlight and warmth. Without these two things, plants, animals and humans would not be able to survive on Earth. Without them, the Earth would be cold and lifeless.

The sun, therefore, is the most important part of the solar system. In fact, without the sun, there would be no solar system.

How big is the sun?

Within our enormous galaxy, the Milky Way, the sun would be considered a fairly small star among millions and millions of others. To us here on Earth, the sun is a massive structure. Its size is difficult for us to comprehend. Across its diameter, the sun measures an amazing 1.4 million kilometres. This is so big that, in theory, we could fit one million Earths inside the sun. If you were to combine all the matter in the entire solar system, the sun would make up 99.9 percent of the total matter in the solar system.

Not only is it a huge structure, but a very heavy one too. The sun weighs an astonishing 2000 trillion trillion tonnes. This is 700 times heavier than all the moons and planets put together. This is an amazing fact when you consider that is made up mainly of two of the lightest gases in the universe. Its mass is so great, however, that the gravitational force created is strong enough to attract all the planets into orbit around it. Our entire solar system is held in place by the sun's gravitational pull caused by its mass.

How hot is the sun?

The hotter an object is, the brighter it glows. Each centimetre of the sun is said to burn as brightly as the light of 250 000 candles. Knowing that the sun is bright enough to light our entire planet, even though it is roughly 150 million kilometres away, gives some idea of how hot it must be. Not only does it light our planet from that distance away, but the sun's heat is even strong enough to burn our skin from that distance. If you have ever accidentally been out in the sun for too long without sunscreen, you will know the damage it can do.

So how hot is it? The temperature on the surface of the sun is approximately 6000 degrees Celsius. At the very core of the sun, where the heat is produced, the temperature reaches a scorching 15 million degrees Celsius.

What is the sun made of?

The sun is not solid like the Earth but is a fiery ball of gases. It is mainly made of hydrogen and helium gases. It does, however, have a number of layers to its structure. At the very centre of the sun is the extremely hot core. This is where the sun's energy is produced. Surrounding this is an outer layer called the convection region. This area contains rising and falling currents of gases.

The visible surface layer of the sun is called the photosphere. The photosphere looks like a violent sea of bubbling, boiling gases. It is this sea of boiling gas that sends out the light and heat that we see and feel on Earth. Above this is thechromosphere. This is the inner layer of the sun's atmosphere. Tongues of flames called spicules dart through this layer, making it look like a flaming forest. The final layer of extremely hot gases is called the corona. The corona is the outer layer of the sun's atmosphere. It sits above the chromosphere like a halo.

Where does the sun's energy come from?

Even though the sun may look as if it is on fire, it is not burning in the same way that wood or coal burns. The heat and light that come from the sun are caused by huge nuclear reactions that happen inside its core.

The enormous size of the sun means that tremendous pressure builds up in its core. This pressure causes hydrogen atoms to crash together to form helium atoms. Every second, about 600 million tonnes of hydrogen atoms crash together. This process creates huge amounts of energy. The energy escapes in the form of heat and light.

It is interesting to learn that each time this process happens, the sun loses a small amount of its mass. This is because it takes four hydrogen atoms to form one single helium atom. The sun loses four million tonnes every second. Imagine how much lighter it will be by the time you finish reading this page.

There is no need for alarm, though. The sun has been shining for the last five billion years and it contains so much material that it will continue shining for many thousands of millions of years yet.

What is a solar eclipse?

A solar eclipse occurs when the moon comes directly between us and the sun. This happens only once every one or two years. It can be quite spectacular. The moon appears to be a similar size to the Sun when viewed from Earth. A solar eclipse causes a dark shadow to fall over the Earth. The light from the Sun is blocked out on Earth for a few minutes.

What are sunspots?

If it were possible to look at the surface of the sun (which you should never attempt as it can cause blindness), you would possibly see some dark blemishes. Within these dark spots, strong magnetic fields occur. The magnetic fields stop the sun's gases from boiling and bubbling in these spots. As the trapped gas in these areas cool, they become dark in colour. These are what we call sunspots.