It's going to bake the Earth to a cinder

TO the Egyptians it was Ra; to the Greeks, Helios; in India it was known as Surya; to the Incas, Inti; the fact you couldn't look at it directly caused the Mayans to call it Kinich Anau, the squint-eyed. Whether it was the only god or just one of them, the Sun was always ranked among the most powerful.

It shouldn't be any surprise that it has been elevated into a god and worshipped by civilisations around the world and throughout history. It is the bringer of light, the foundation stone of life. It brings us warmth, it nurtures our crops, it even regulates our lives, timing our days and our years.

But how much do we know about the Sun? For all the influence it has over us, what do we understand about this ball of flaming gas, which gives off enough energy in one hundredth of a second to supply mankind's energy needs for 10,000 years?

Science writer David Whitehouse aims to fill that gap. Science correspondent for the BBC and contributor to newspapers and magazines, following a career as an astronomer at Jodrell Bank observatory and at NASA, he has written a biography of the Sun, a combination of science, history and anecdote.

It follows his biography of the Moon, but tackling the Sun provided a very different challenge. "The Moon is a ball of rock, the Sun has a much higher place in the ecology of the universe, and there is far more science associated with the Sun," he says.

"The Sun is almost alive in the way it is an energy provider for the universe. Basically, it doesn't matter if the Moon is there or not, it would not make a great deal of difference to humanity or planet Earth.

"But not only does the Sun keep the Earth warm, it is the very reason the Earth is here."

But the Sun is not exceptional. Its story is one repeated throughout the cosmos, of stars that give off light for billions of years. And we should be glad that the Sun is common. Bigger and brighter stars burn out quicker; smaller stars aren't bright enough to sustain life on orbiting planets.

"It may be that stars like the Sun, which is the most average type of star, are the life-givers of the universe. It is around such stars, that are fairly constant and give off light and heat for billions of years, that life can be nurtured," says Dr Whitehouse. "In saying something about the Sun, you are saying something about life."

But it is difficult to comprehend the size and power of the Sun. It generates the equivalent of 80 billion hydrogen bombs every second, and has been doing that for four and a half billion years. It will carry on doing that for another four, maybe five, billion years. Alongside this, our attempts to solve our energy problems appear puny.

It measures 1.49 million km across. A string of sunspots seen in 1984 was spread over 280,000km, more than 20 times the diameter of the Earth. The temperature at the surface is 6,000 degrees. But these numbers are too large to mean much to us.

For ancient civilisations, the Moon and the Sun were often linked in the stories of how they came into being. Often, the Sun was the most important, but this was far from universal. As well as being bright and strong, some saw the Sun as brutal and unsubtle, typically male characteristics. The Moon was changeable, difficult to understand and linked with water through the tides, and was portrayed as the woman pulling the strings.

But while our lives were once governed by the Sun, we are now gradually becoming divorced from its cycles. Even a century ago, our forebears had a much more intimate relationship with the Sun than we do today.

Now, central heating and electric lights mean the seasons have a much more limited effect on our lives. Even our eating habits have lost the bond they had with the Sun. The idea of seasonal fruit and vegetables has been lost by the ability to transport them cheaply around the world.

But it would be a mistake to start taking the Sun for granted. "Not only is it important for us to understand because of its effect on our climate, but it is also important because of its effect on our health, sunburn and seasonal affective disorder," says Dr Whitehouse.

"We often only notice it when things go wrong, but it has its effect everywhere, if you know where to look. The reason people living near the equator have dark skins is purely an adaptation to the amount of sunlight."

But eventually, this giver of life will bring death, although not in the way many people imagine. The Sun will not swell up and explode, destroying the Earth; instead, it will leave it scorched and charred, with all life obliterated. Thankfully, this is still some way away. If the Sun's life ran from midnight to midnight, it would now be at 10.30am, youthful middle age.

"We know exactly what is going to happen to the Sun, because we can see stars like our Sun which are older and going through this process," says Dr Whitehouse. "Eventually it will get brighter and swell up to become a red giant.

"It will swallow up the planets Mercury and Venus, but it won't quite swallow up the Earth. It will bake the Earth to a cinder, the Earth will be sterilised and become nothing but dry and barren rock.

"After a few tens of millions of years of that, it will then shrink down to become a white dwarf and it will cool and nothing will ever happen to this cosmic cinder. It will drift through space with the remnants of the planets around it for ever, getting colder and colder."

Through the billions of years of the universe, the amount of time the Sun is a ball of flame is as nothing compared with how long it will spend as a cinder, but it is as a burning disc that it has not only given us life, but also seems to have a life of its own.

"You almost get the feeling that it has this extra dimension," says Dr Whitehouse. "It is almost like a cell, it reacts in the same ways. Although it is a purely automatic ball of gas which only works according to the laws of physics, when you look at it in action it does almost seem as if it is alive."

* The Sun: A Biography by David Whitehouse (Wiley, £9.99).