A (36) of the physical and chemical nature
of life must begin; not on the Earth,: but in the Sum In fact, it is. at the
Sun% very center. It is here that is to be found the source of the energy that
the Sun (37) pours out into space as light and heat. This
energy is liberated at the center of the Sun as billions upon billions of nuclei
of (38) atoms collide with each other and fuse together to
form nuclei of helium (氦). And, in doing so, it (39) some of
the energy that is stored in the nuclei of atoms. The output of light and heat
of the Sun requires that some 600 million tons of hydrogen be (40)
into helium in the Sun every second. This the Sun has been doing for
several thousands of millions of years. The nuclear energy is
released at the Sun’s center as high-energy gamma (41) , a
form of electro-magnetic radiation like light and radio waves, only of very much
shorter (42) . This gamma radiation is (43)
by atoms inside the Sun, to be re-emitted at slightly longer wavelengths.
This radiation, in its turn, is absorbed and reemitted. (44)
, it passes through the X-ray part of the spectrum (频谱) , eventually
becoming light. At this stage, it has reached what we call the solar surface and
can escape into space, (45) . A very small fraction of the
Sun’s light and heat is emitted in such directions (46)
.