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The Solar System consists of the Sun and a group of bodies that orbit around it: the planets, dwarf planets, satellites and comets.
The structure of the Sun
Video 3: Our Solar System
3.1. The Sun
Talking book
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 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
Talking book
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.
Dwarf planets:rocky bodies that move around the Sun in orbits that are occupied by other bodies.
Comets: bodies composed of ice, rock and dust, which orbit the Sun in distant orbits.
Asteroid belt: formed by irregular bodies that orbit the Sun between the orbit of Mars Jupiter.
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).
Satellites: rocky bodies that orbit planets.
3.3. The movements of the planets
Talking book
Animation 1: How to construct a Solar System
All the bodies in the Universe are continuously moving. The planets in our Solar System move in two different ways: revolution and rotation.
Revolution is the movement of the planets around the Sun. The period of time that a planet takes to complete one revolution around the Sun is called a year.
The orbits of the planets in the Solar System are elliptical and are on approximately the same plane. The planets orbit the Sun in an anticlockwise direction.
Revolution
Rotation is the movement a body makes on its own axis. The period of time that a planet takes to complete one rotation is called a day.
Key concepts
The Solar System is located in the Orion Arm in the Milky Way.
Revolution is the movement that planets and other bodies make around the Sun.
Rotation is the movement that planets and other bodies make on their own axis.
Apart from Uranus, which rotates on a horizontal axis, planets rotate on an axis which is perpendicular to their orbita orbital plane. Like revolution, the rotation of most planets is in an anticlockwise direction (except for Venus and Uranus).
Axis of rotation of the planets
1
Activity 14 Which planets take longer to orbit the Sun: the inner planets or outer planets?
