Tuesday, May 29, 2007
Inside The Turbulent Sun
To the non-astronomer, the Sun is a model of constancy - a featureless white globe that has shone steadily throughout human history. But astronomers know the Sun to be a nuclear powerhouse in constant turmoil, and it may be far less reliable than we think.
The Sun is a vast ball of hot gas, principally hydrogen, big enough to swallow up 1.3 million Earths. To express its weight in tonnes you would need to write a 2 followed by 27 noughts. This weight, some 3000 000 times that of the Earth, crushes the Sun's core to a pressure of over 300 million times that of our atmosphere.
The temperature at the centre of the Sun is 15 000 000 degree C (27 000 000 degree F). In this furnace rages the nuclear reaction that creates the Sun's light and heat. It is the same reaction that powers the H-Bomb - the nuclear 'burning' of hydrogen into helium. As in all nuclear reactions, matter is converted into energy. The amount of helium produced in the reaction is only 92.3 per cent of the amount of hydrogen used up. The difference has been converted into light, heat, X-rays and other forms of energy. Four million tonnes of the Sun's matter vanish in this way each second.
At the surface, the Sun's temperature is a mere 5800 degree C (10 400 degree F). The visible surface is mottled - bright where hot gas has just risen from the depths, darker where a cooled area is about to descend. Invisible, looping magnetic fields occasionally break through the surface from the depths beneath. The magnetic fields block the flow of energy, so the areas of the surface where the loops emerge and re-enter become relatively cool and appear as dark sunspots. Prominences - spectacular clouds of glowing red hydrogen many times the size of the Earth - climb into the solar sky and fall back again.
Can a body as violent as the Sun be relied upon not to change its behaviour in the future - not to scorch us or let us freeze to death?
Constant monitoring shows many irregularities. It appears, for example, that since 1979 the Sun has cooled by one-tenth of 1 per cent. This minor fluctuation will probably reverse, staying in step with regular ups and downs in general solar activity, such as the number of sunspots. All theorists agree that the Sun will continue to support life on Earth for about another 5000 million years.