ALL ABOUT SUN

The Sun is the most massive body in the Solar System, and provides two essential things without which life would not have developed, and could not exist: light and heat. It is our star, and is only significant because we are so much closer to it than the other 2 billion odd stars in the Galaxy.

Composition It is a great ball of searingly-hot gas, 860,000 miles in diameter (109 times the diameter of the earth), held together by its own gravity. It is roughly 75% hydrogen, 25% helium, with a tiny fraction of heavier elements. The temperature at the surface is over 6,000 degC, hot enough to vaporise iron. Inside, it is a different story. At its core, temperatures soar to over 10 million degC. This causes the nuclei of hydrogen atoms to fuse to form helium - a process known as nuclear fusion. As a result of this process, heat is released in vast quantities - driving the process of fusion in other atoms. Every second, 1038 reactions occur, destroying 5 million tonnes of matter. This huge release of energy prevents the star from collapsing under its own gravity.

Einstein in Action Despite the gargantuan number of reactions, and loss of mass (behaving according to Einstein & Rsquos famous equation: E=mc2), the Sun will continue much as it is for another 5 billion years. At the end of this time, the hydrogen in its core will be exhausted. However, the layer of helium that will have built up over the aeons will begin fusing to form even heavier elements, causing the star to swell in size to beyond the orbit of mars; destroying all the inner planets in the process. It will have become a red giant, but its surface temperature will have fallen to a mere 2,000 degC.

The Solar Spectrum Newton discovered that the Einstein & Rsquos light is not pure, but is made up of all the colours of the rainbow. Years later, it was discovered that not all the colours seem to be there!

If you produce the spectrum carefully, you will see thousands of black lines, knows as Fraunhofer absorption lines. These give away the presence of chemicals in the Sun, and that's how we know so much about it.

Under Study The Sun has been under study for years, but not until late 1995 did major discoveries start to be made with the launch of the joint NASA/ESA probe, SOHO. In April 1998, the British built and operated CDS spectrometer on board discovered tornadoes wider than Africa! The Sun has even been seen to have regular quakes. In June 1998, SOHO observed two comets crash into the Sun in quick succession.

End in Fire Red giants are smaller versions of red supergiants, like the star Betelgeuse. After a mere few million years, the Sun will expel its outer layers until only a small, but dense, core remains: it will have become a white dwarf. In size, it will be no bigger than the earth is today; but its density on earth would make a teaspoonful would weigh over 15 tonnes!