Man's physical universe


The Source of the Sun's Energy Is Still Unknown.


The amount of energy that finally reaches the earth is

very large.

Measured by the pyrheliometer, it is found that the earth receives

230,000,000,000,000 horsepower, continuously, or about 160,000 horsepower

for every human being. The amount of energy radiated by the

sun would be sufhcient to melt a 40-foot shell of ice around the sun

within one minute. The generators at Boulder Dam will be able to

generate 663,000 horsepower, which means that it will be able to

harness about 1/340,000,000 of the sun's energy which reaches the


When we consider that the earth and its atmosphere intercept only

about one two-billionth of the total energy emitted by the sun, and

when we consider how much energy this two-billionth represents, we

wonder whether the sun is not gradually growing cooler as it loses all

of this energy.

Indelible records preserved in the rock layers of the earth indicate

that there has been no noticeable permanent change in the amount of

energy that the earth has received during the past billion years.


observation indicates either that there is so much energy in the sun

that the relative amount lost in a billion years is negligible or that

there are changes taking place within the sun which liberate energy.

Hermann HelmhoUz (1821-1894), a German physicist, suggested that

energy was evolved by a gradual condensation process within the sun,

but later calculations showed that such a process would account for less

than one hundred-thousandth of the energy it has already lost.

Astronomers agree that the sun would show a decrease in temperature

after a period much shorter than a billion years if the energy lost

by the sun was not renewed continuously.

Sir Isaac Newton suggested that matter itself might be changed into

radiations, but it remained for recent studies of radioactivity and

nuclear chemistry to provide some concrete evidence which places

such an idea within the range of possibility.

It is now supposed that this energy is liberated either by constructive

or disintegrative processes taking place within the sun which change

matter into energy.

Radioactivity gives off a great deal of heat and produces helium as a


The fact that there is considerable helium in the sun was

responsible for the re :ioactive-decomposition theory of the source of

the sun's energy. More recently, however, a reaction in which matter

is built up rather than decomposed has been found to fit all of the

known facts.

A recent hypothesis, advanced by Bethe, that seems reasonable is

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