Download The Sun: Our Closest Star and a Nuclear Fusion Reactor

The Sun: Our Closest Star and a Nuclear
Fusion Reactor
The first in a series of articles on the Universe. Starting with the solar system and moving out
into the Universe. A descriptive look at what's out there.
Imagine a golf ball in the middle of a football pitch. Imagine the Earth to be the size of the
golf ball and the football pitch to be circular. The Sun would be approximately the size of the
circular football pitch.
The Sun: Nuclear Furnace Contains 99.8% of Solar System's Mass
The Sun is 1 400 000 km in diameter and is composed of 75% hydrogen and 25% helium. Its
internal core temperature is 14 000 000 degrees centigrade whereas the external surface
temperature is approximately 6 000 degrees centigrade. The Sun has a mass of 2 000 billion
tonnes.
The Sun's Energy.
The power source of the Sun is a nuclear fusion reaction where hydrogen atoms fuse together
at the huge temperatures to form helium. Essentially what happens is that in the process of
forming hydrogen from helium there is small loss of mass. This mass is converted to energy
such as heat and light and provides the fuel to sustain the nuclear fusion reactions within the
Sun's inner core. It is a simply amazing thought that matter can be converted directly into
energy.
The Sun's Structure.
Similar to the Earth, the Sun has many different layers that define its structure. However
unlike the Earth, the Sun is an incredibly hot ball of gas with no solid surface.
The Sun has a definite structure and the layers are:
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The central core. This is around 10% of the Sun's mass and where the nuclear fusion
takes place. It is incredibly hot at around 14 000 000 degress centigrade.
Radiation zone. In this zone the incredibly hot region energy starts moving towards
the Sun's surface through the process of radiation. The region is approximately 85%
of the Sun's diameter.
Convection zone. In this zone energy is transported to the surface by huge convection
currents. Atoms are cool enough to retain their electrons and this region accounts for
approximately 15 % of the Sun's diameter.
Photosphere. This is the incredibly bright layer which can be seen from Earth. All
light from the Sun is transmitted outwards by the photosphere. The layer is about 500
km thick.
Chromosphere. This is the outermost layer of the Sun and strangely enough is hotter
than the photosphere. The temperature rise is thought to be due to the huge vibrations
and noise from chemical and nuclear processes happening within the Sun. It is around
10 000 degrees centigrade and extends 5000 km out into space.
Corona. This region is where the hot gases are flowing out into space. It is the bright
gaseous edge of the Sun only visible during a solar eclipse. Gases that flow further out
into space from the corona are called the solar wind.
In his book Stars of the Southern Skies, Patrick Moore not only discusses the structure of the
Sun but also how to set up the equipment for solar observations.
The Sun's Future.
The Sun is a incredibly large and very hot ball of gas powered by nuclear fusion. It provides
the energy which sustains life on Earth. The Sun is middle aged and will live for another 4 to
5 billion years in its present form. Towards the end of its life it will expand to form a red
giant as the nuclear fuel of hydrogen begins to run out. During this time the Sun will expand
and consume Mercury and possibly Venus. It will also blow off Earth's atmosphere turning
the planet into a charred lifeless rock. Eventually the Sun will throw off its own atmosphere
forming a planetary nebula. It will then cool and collapse in size to a hot white dwarf. As the
Sun cools further it will finally form a black dwarf.
Life on Earth will not be possible in 4 billion years time as the planet will be far too hot. For
life to exist beyond this we must go to the stars.
Further Reading
Moore, Patrick. Stars of the Southern Skies. David Bateman Ltd, Auckland, New Zealand,
1994.