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3.
THE SOLAR SYSTEM
3.1.
The Sun
The Sun was born 4600 million years ago and it is approximately 40000 light years
from the nucleus of the Milky Way. It is a medium-sized yellow star with a surface
temperature of 5500 ºC. It consists mostly of hydrogen and helium, although there
are other elements such as oxygen, carbon and iron.
The Sun
rotates
on its axis in an anticlockwise
4
direction. One
rotation
takes
approximately 28 days. Its mass is 2 x 1030 kg, which is almost 99% of the total
mass of the Solar System. The material that makes up the Sun is divided into
different layers.
❚
The
inner layers
contain the heaviest materials. In the innermost layer of the
sun, the core, nuclear fusion reactions occur that generate energy.
❚
The
outer layers
contain the lightest materials. The most external layer is the
layer we can see from Earth, called the
photosphere
. Energy is released from
here in the form of light and heat.
3.2.
The structure of the Solar System
The Solar System consists of a series of celestial bodies that revolve around its star,
the Sun. The celestial bodies are classified according to their size, composition and
the orbit they follow.
The Solar System
consists of the Sun and the celestial bodies that orbit
it.
Planets
: rocky bodies that move around the Sun, in orbits that are not
occupied by other bodies. Depending on their distance from the Sun, they
are classified as
inner (rocky) planets
(Mercury, Venus, Earth and Mars); and
outer (gaseous) planets
(Jupiter, Saturn, Uranus and Neptune).
Asteroid belt
:
formed by
irregular bodies
that orbit the
Sun between
the orbit of
Mars Jupiter.
Comets
: bodies
composed of ice,
rock and dust,
which orbit the
Sun in distant
orbits.
Satellites
: rocky bodies that orbit planets.
Dwarf planets
:
rocky bodies that
move around the Sun in orbits that
are occupied by other bodies.
The structure of the Sun
4
anticlockwise
:
in the opposite
direction to the hands of a clock
