In ancient times the Romans called the Sun Sol, the Greeks called it Helios. The Sun is at the center of a planetary system that is called the Solar system, after the Roman name for the Sun.

The Sun is a star. It is a giant ball of hydrogen gas that is being turned into helium by massive forces caused by gravity. As hydrogen atoms combine to form helium, energy is given off. This make the Sun very hot, around 6,000 Kelvin at the surface, millions of Kelvin at the core.

The other stars in the sky are also burning balls of gas, most are smaller than our sun, some are much bigger.

Our Sun is about 5 billion years old. It formed from a vast cloud of gas called a nebula. Most of the light gas collected together at the center of the Nebula under the influence of gravity. This became the Sun. At a specific point gravitational forces started to make hydrogen atoms fuse together and the Sun ignited, though it isn't on fire in the same way wood burns.

The Sun is at the center of our Solar System. Earth revolves around the Sun, but not in a perfect circle. The orbit of the Earth is elliptical and the Sun lies at one of the ellipse focal points. At its closest, Earth is 147 million kilometers from the Sun. At its furthest point, Earth is 152 million kilometers from the Sun. One revolution of the Earth takes 365.25 days, or one year.

The sun has a diameter of around 1.4 million kilometers, big enough to fit 1.3 million of Earths in it. The Sun makes up over 99% of the volume of the solar system.

The process by which hydrogen gas is converted into helium gas is called Nuclear fusion.

Atoms are made of elements called protons, neutrons and electrons. The center of an atom is called the Nucleus and is made from an equal number of protons and neutrons.

Protons have a positive charge and if they were to come close they would repel each other, the neutrons have no charge and help separate the protons allowing them to stick together.

Electrons are negatively charged and exist around the Nucleus, balancing its charge and making an atom neutral. Sometimes an atom will lose an electron, or gain one, making the atom either negative or positive. These are called Ions.

Hydrogen atoms are the smallest type of atom. They have one proton, one neutron and one electron. This gives hydrogen an Atomic number of 1. Helium is the next smallest having an atomic number of 2 (two protons, two neutrons and two electrons). Two hydrogen atoms can be combined to produce one helium atom.

This process is achieved by the extraordinarily high gravitational forces at the center of the Sun due to the large amounts of matter that make up the Sun.

When two hydrogen atoms are combined in this way, heat is created. This heat builds up inside the sun and atoms slowly make their way to the outside. As they do they cool and fall back down towards the center again. This cycle is called convection and it can take millions of years for an atom to complete the cycle.

The average temperature at the surface of the sun is around 6,000 Kelvin. Not every point is at the same temperature though. Some areas are hotter than others. The cooler areas appear darker and are called sun spots.

Being cooler than the lighter areas Sunspots are much denser and have a higher gravitational force because there is more mass. They are also associated with high magnetic fields and come in pairs, equivalent to the North and South Pole of a magnet.

Sunspots come and go on a regular 11 year cycle, building in intensity and then declining. The cycle was discovered by Samuel Heinrich Schwabe (1789-1875), a German astronomer who studied sunspot activity very closely.

A Solar flare is the result of a huge explosion of material from the Sun that usually appear over sunspots. They appear as very bright spots as tons of high energy particles are released in extremely hot streams.

As the sun converts nuclear fuel into energy it gives off streams of atomic particles. These particles race away from the sun at fantastic speeds and some eventually approach the planets. Earth is shielded from these dangerous particles by it's magnetic field. It is the solar wind that create the tails of comets, which will always appear to heading away from the sun rather than trailing behind the comet.

The Sun depends on a supply of hydrogen for fuel. The hydrogen is converted into helium by the force of gravity at the sun's center. Once this fuel is used up it will start to change.

In about 5 billion years the Sun's outer layers will start to expand. As it does it will cause the water on Earth to boil away and life will eventually cease to exist.

The sun will continue to expand and turn red. As it does it will consume the Earth. This stage will last about 100 million years. When the star finally runs out of fuel it will turn into a white dwarf star hardly visible from the remaining planets.