Mankind has always been fascinated by the heavens. Early people, like the ones who built Stonehenge, believed the Sun was a god and worshipped it. The Egyptians, through geometry and astronomy, believed they had found heaven. Even the Romans and Greeks studied the skies. The ancients grouped the stars into constellations, which were named in various ways. The constellations we know today are Greek, with Latin names, such as Ursa Major. So let's look at the facts and take a journey through the life of a star.

The Sun would have begun its life as a nebula. A nebula is a cloud of gas and dust that has slowly formed over time by atoms in space coming together. Many stars are born at the same time, some of which disperse, while others are held together by gravity.

The second stage in a star's life is when it changes into a protostar. Protostars are formed when parts of the nebula collapse due to gravity. Each part becomes most dense at its centre. Here heat is trapped and a protostar is formed. When the protostar is hot enough it changes again. Nuclear fusion reactions take place and massive amounts of energy are released. The protostar is now called a T. Tauri type star.

Over time, the rest of the nebula is blown away. Gravity at the centre of the star pulls hydrogen atoms towards it, where they smash together and fuse. This forms helium and energy. The pressure at the centre of the star keeps it expanded. Now the T. Tauri type star has changed into a main sequence star.

The Sun as we know it is currently in this state. It will spend approximately 10,000,000,000 (ten billion) years as a main sequence star. It's becoming obvious why astronomers today and from millennia ago love their work! Some more massive, hotter stars use up their fuel more quickly and only spend a short time as main sequence stars. After these ten billion years, the amount of light the star gives out increases and it becomes more dense and hotter. The star next changes when all the hydrogen is used up.

By now, the centre is so hot that the star expands and the surface cools. The cooled surface turns red, hence the new star's name, a red giant. Once again the star changes. The helium begins to join with itself to form carbon. The star has now changed into a Cepheid. The star gradually shrinks as it loses its outer layers. By now the star is close to death and we're nearing our journey's end.

The next stage in a star's life is when it changes into a White Dwarf. The outer layers of the star become unstable and blow away into space. The inner layers then don't have enough energy to remain expanded and so they collapse. The star has now become a White Dwarf and will eventually fade to a Black Dwarf, a dead star with no light or heat. This signifies our journey's end and the end of the star's life.

However, not all stars die as white dwarfs. Some stars are so massive that when they collapse, they explode. This explosion is called a supernova. The core of the supernova may remain as a neutron star.

A neutron star is the type of star formed when some stars collapse. When a star with between about 1.4 and three times the sun's mass collapses, it leaves a core called a neutron star.

In 1054, the Chinese recorded a star so bright that it could be seen in daylight. The star was actually a supernova. Today, we can see its remains: the Crab Nebula. The core of the exploding star is now a pulsar, rotating 30 times per second. A pulsar is a fast-spinning neutron star that flashes signals towards Earth as it spins. Pulsars were discovered by two British astronomers, Jocelyn Burnell and Antony Hewish.

Unusual things happen to stars at the end of their lives if their mass is more than three times the mass of the sun. It will collapse, becoming more and more compact. The star continues to collapse until it becomes so dense that not even light can escape its gravity. It has become a black hole with a point of infinite density (singularity) at its centre.

So next time you're lying on the beach, sunbathing or looking up at the sky at night, stargazing, spare a thought for the incredible journey from nebula to nova.