填空题

A summary of the physical and chemical nature of life must begin,
not on the Earth, but in the Sun, in fact, at the Sun’s very center. It is here
which is to be found the source of the energy that the Sun constantly pours 41 ______
out into space light and heat. This energy is librated at the center of 42 ______
the Sun as billions upon billions of nuclei of hydrogen atoms collide
with each other and fuse together to form nuclei of helium, and doing 43 ______
so, relieve some of the energy that is stored in the nuclei of atoms. 44 ______
The output of light and heat of the Sun requires that some 600 million
tons of hydrogen are converted into helium in the Sun every second. 45 ______
This the Sun has been doing for several thousands of millions of year.
The nuclear energy is released at the Sun’s center as high-energy
gamma radiation, a form of electromagnetic radiation like light and
radio waves, only of very much short wavelength. This gamma radiation 46 ______
is absorbed by atoms inside the Sun to be reemitted at slight longer 47 ______
wavelengths. This radiation, in its mm is absorbed and reemitte& As the
energy filters through the layers of the solar interior, it passes through
the X-ray part of the spectrum eventually becoming light. At this stage,
it has reached that we call the solar surface, and can escape into space 48 ______
without being absorbed further by solar atoms. A very small fraction of
the Sun’s light and heat are emitted in such directions that after 49 ______
passing unhindering through interplanetary space, it hits the Earth. 50 ______