Why doesn't the sun get smaller or bigger
The Sun is a giant ball of hydrogen and helium gas. And it is on fire. If we heat a balloon of gas, it expands. That is why a hot air balloon rises. Because the air in the balloon has expanded under heat, it is lighter than normal air, and capable of lifting a basketful of people into the sky.
If the same principle applies, it seems logical to expect that the Sun’s heat would make its own volume expand. We know that it doesn’t do so. In fact, to most people, the Sun seems to behave with complete reliability a constant and unchanging source of light and heat.
A solution to the problem of why the Sun doesn’t grow in size was found in the 1920s by a British astronomer, Arthur Eddington. He argued that, if the Sun consists solely of gas, its force of gravity should draw that gas into a small and fairly tight ball. Because the Sun doesn’t collapse in this way, another force keeps it in a balanced state. That force, he and others deduced, is heat. As gravity pulls inwards, heat pushes outwards. One force cancels out the other. Those twin forces, pulling equally, ensure that the Sun can’t get any bigger. Nor for a long time can it become any smaller.
From these deductions came others. Already, the Sun’s force of gravity was known. Eddington then calculated how much heat was needed to produce an equivalent and balancing force, and found that it was millions of degrees. At its heart, the Sun’s temperature is 15 million°C (27 million°F).
American physicist George Gamow worked out that a pinhead brought to the same temperature, if that were possible, would set fire to everything within a radius of 100 km (60 miles). So vast is the Sun’s ball of gas that by the time heat reaches the surface it has cooled to a modest 5800°C (10 400°F).
The Sun’s surface is in a state of constant turbulence as hot streams of gas break through. Cooler gas, more condensed and therefore heavier, sinks downwards into the furnace. These great flows are visible from Earth, giving the Sun a mottled appearance of light (hot) areas and dark.
If the same principle applies, it seems logical to expect that the Sun’s heat would make its own volume expand. We know that it doesn’t do so. In fact, to most people, the Sun seems to behave with complete reliability a constant and unchanging source of light and heat.
A solution to the problem of why the Sun doesn’t grow in size was found in the 1920s by a British astronomer, Arthur Eddington. He argued that, if the Sun consists solely of gas, its force of gravity should draw that gas into a small and fairly tight ball. Because the Sun doesn’t collapse in this way, another force keeps it in a balanced state. That force, he and others deduced, is heat. As gravity pulls inwards, heat pushes outwards. One force cancels out the other. Those twin forces, pulling equally, ensure that the Sun can’t get any bigger. Nor for a long time can it become any smaller.
From these deductions came others. Already, the Sun’s force of gravity was known. Eddington then calculated how much heat was needed to produce an equivalent and balancing force, and found that it was millions of degrees. At its heart, the Sun’s temperature is 15 million°C (27 million°F).
American physicist George Gamow worked out that a pinhead brought to the same temperature, if that were possible, would set fire to everything within a radius of 100 km (60 miles). So vast is the Sun’s ball of gas that by the time heat reaches the surface it has cooled to a modest 5800°C (10 400°F).
The Sun’s surface is in a state of constant turbulence as hot streams of gas break through. Cooler gas, more condensed and therefore heavier, sinks downwards into the furnace. These great flows are visible from Earth, giving the Sun a mottled appearance of light (hot) areas and dark.
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