Why doesn't the sun ever burn out | How long will the sun last?
If you fail to stoke a fire, its flames at some time will die. Yet the great fire of the Sun has burned nonstop for about 5000 million years with po apparent sign of going out. We, on Earth, soak up a tiny fraction perhaps one hundred millionth of the Sun’s vast energy. The rest of its awesome output of heat and light vanishes beyond the planets and into space.
People in many cultures regarded the Sun as a miraculous gift from the gods, quite different from earthly fires and therefore not likely to fail them unless the gods were made angry. We now know that the Sun will eventually burn away. Tests show that its temperature fluctuates.
Since 1979, it seems to have cooled by one tenth of 1 per cent, but that is not a sign that the great fire is going out. Space scientists believe that, because of the Sun’s volatile nature, this minor change may soon be reversed.
The Sun is composed of almost 75 per cent hydrogen and 25 per cent helium, plus much smaller amounts of oxygen, carbon, neon, nitrogen, magnesium, iron and silicon. It is known as a main sequence star, one that shines by burning hydrogen. At the Sun’s heart, the hydrogen was once compressed with such force that it started a nuclear reaction. In this giant furnace, the hydrogen is converted by nuclear fusion into another combustible gas, helium, in a reaction similar to that in an H-bomb. Thus, the Sun is both burning fuel and creating it. As the hydrogen store diminishes, its stock of helium grows. The light and heat coming now from the Sun were actually produced in its core many millions of years ago.
When we burn fuel on a fire, we are converting matter wood or coal partly into energy. The more efficient the fire, the more heat it produces. The Sun is an extremely efficient furnace, but even so the helium it generates to keep the great fire going is only 92.3 per cent of the hydrogen it burns. The other 7.7 per cent vanishes in several forms of energy, mainly heat, light and X-rays. This loss of hydrogen is slight when compared to the Sun’s enormous bulk. Even though it is composed of light gas, the Sun weighs some 300 000 times as much as the Earth. And it loses about 4 million tonnes of matter every second.
Scientists predict that the Sun has enough hydrogen to keep the fire going for another 5000 million years, about as long again as it has already burned. If humans still inhabit the Earth at that time, they and all other life will perish in a terrifying holocaust.
Before its great fire dies, the Sun will turn into a red giant, bloated to about 100 times its current size. First, it will engulf Mercury and then Venus, the nearest planets. The Earth’s atmosphere, which normally shields it from the intense heat of the Sun, will drift away. Then the Earth’s oceans will boil and vanish in steam. Without the cooling effects of its atmosphere and oceans, Earth itself will turn into a massive ball of fire. Mars will disintegrate next.
The Sun will become what astronomers call a ‘white dwarf’, a star with a tiny, white hot core. Now very unstable, it will produce no energy. Gradually, like the heart of a dying fire, it will change colour, turning in this case from white to yellow and red until, finally, as a black dwarf, it disappears from sight.
If that sounds depressing, take heart! If the Sun switched off its power tomorrow, it would be ten million years before its surface cooled sufficiently for anybody on Earth to feel the chill. In 5000 million years’ time, humans may well have found an answer to impending doom.
People in many cultures regarded the Sun as a miraculous gift from the gods, quite different from earthly fires and therefore not likely to fail them unless the gods were made angry. We now know that the Sun will eventually burn away. Tests show that its temperature fluctuates.
Since 1979, it seems to have cooled by one tenth of 1 per cent, but that is not a sign that the great fire is going out. Space scientists believe that, because of the Sun’s volatile nature, this minor change may soon be reversed.
The Sun is composed of almost 75 per cent hydrogen and 25 per cent helium, plus much smaller amounts of oxygen, carbon, neon, nitrogen, magnesium, iron and silicon. It is known as a main sequence star, one that shines by burning hydrogen. At the Sun’s heart, the hydrogen was once compressed with such force that it started a nuclear reaction. In this giant furnace, the hydrogen is converted by nuclear fusion into another combustible gas, helium, in a reaction similar to that in an H-bomb. Thus, the Sun is both burning fuel and creating it. As the hydrogen store diminishes, its stock of helium grows. The light and heat coming now from the Sun were actually produced in its core many millions of years ago.
When we burn fuel on a fire, we are converting matter wood or coal partly into energy. The more efficient the fire, the more heat it produces. The Sun is an extremely efficient furnace, but even so the helium it generates to keep the great fire going is only 92.3 per cent of the hydrogen it burns. The other 7.7 per cent vanishes in several forms of energy, mainly heat, light and X-rays. This loss of hydrogen is slight when compared to the Sun’s enormous bulk. Even though it is composed of light gas, the Sun weighs some 300 000 times as much as the Earth. And it loses about 4 million tonnes of matter every second.
Scientists predict that the Sun has enough hydrogen to keep the fire going for another 5000 million years, about as long again as it has already burned. If humans still inhabit the Earth at that time, they and all other life will perish in a terrifying holocaust.
Before its great fire dies, the Sun will turn into a red giant, bloated to about 100 times its current size. First, it will engulf Mercury and then Venus, the nearest planets. The Earth’s atmosphere, which normally shields it from the intense heat of the Sun, will drift away. Then the Earth’s oceans will boil and vanish in steam. Without the cooling effects of its atmosphere and oceans, Earth itself will turn into a massive ball of fire. Mars will disintegrate next.
The Sun will become what astronomers call a ‘white dwarf’, a star with a tiny, white hot core. Now very unstable, it will produce no energy. Gradually, like the heart of a dying fire, it will change colour, turning in this case from white to yellow and red until, finally, as a black dwarf, it disappears from sight.
If that sounds depressing, take heart! If the Sun switched off its power tomorrow, it would be ten million years before its surface cooled sufficiently for anybody on Earth to feel the chill. In 5000 million years’ time, humans may well have found an answer to impending doom.
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