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Age of the sun.

It had been assumed for thousands of years that the Sun was eternal and changeless (and would be until God wished to put it to an end). The discovery of sunspots (see 1610) had shaken this belief but not destroyed it.

Once the law of conservation of energy was well established (see 1847), however, the shining of the Sun had to be questioned. Light and heat were energy, and this could not be created out of nothing. Where, then, did the Sun obtain the energy that had kept it shining brilliantly enough to warm the Earth at a distance of nearly a hundred million miles for all the many thousands of years of history? It could not be ordinary burning, for the entire substance of the Sun would have been consumed in a mere fifteen hundred years in that case.

Helmholtz, who had been the one to establish the law of energy conservation, pondered the matter and by 1853 had decided that the only energy supply that would suffice was that of the Sun's own gravitation.

Slowly, the Sun's globe must be contracting, and the falling inward of that huge mass must be supplying the energy that was converted into light and heat.

This must be the continuation of a process that had begun when a gigantic cloud of dust and gas had contracted to form the Sun in the first place (see 1796).

In order to supply light and heat at the current rate, Helmholtz concluded, the Sun must have contracted from a size filling the orbit of the Earth to its present size in something like twenty-five million years. That meant Earth could be no older than that. Moreover, it meant that in another ten million years, the Sun would be too small and cool to support life on Earth.

This conclusion came as a great shock to geologists, who already thought the Earth must be considerably older than twenty-five million years. It was to be another half-century before the controversy was settled-in favor of the geologists.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
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