sample essays of IELTS

45 The source of Energy

A summary of the physical and chemical nature of life must begin, not on
the Earth, but in the Sun; in fact, at the Suns very center. It is
here that is to be found the source of the energy that the Sun
constantly pours out into space as light and heat. This energy is
librated at the center of the Sun as billions upon billions of nuclei of
hydrogen atoms collide with each other and fuse together to form nuclei
of helium, and in doing so, release 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 converted into helium in the
Sun every second. This the Sun has been doing for several thousands of
millions of year.

The nuclear energy is released at the Suns center as high-energy gamma
radiation, a form of electromagnetic radiation like light and radio
waves, only of very much shorter wavelength. This gamma radiation is
absorbed by atoms inside the Sun to be reemitted at slightly longer
wavelengths. This radiation , in its turn is absorbed and reemitted. 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 what we call the solar surface, and can
escape into space without being absorbed further by solar atoms. A very
small fraction of the Suns light and heat is emitted in such
directions that after passing unhindered through interplanetary space,
it hits the Earth.