THE EARTH AND THE UNIVERSE.

The universe.

The universe appeared 13. 700 million years ago with the “Big Bang”, the explosión of a small mass which contained all the existing matter and energy.

The universe is made of:

•       Stars a celestial body which produces its own light and heat.

•       celestial bodies:

Ø  planets, a celestial body which rotates around a star and does not produces its own light and heat.

Ø  satellites, a celestial body which rotates around a planet.

•       interestelar matter (dust and gas).

The Milky Way.

In the universe, there are millions of groups of stars called galaxies. Each one of them contains thousands of million of stars and planetary systems. One of them is the Milky Way, in which the Solar System is located.

The Milky Way seen from Earth.

The Solar System.

The Solar System is the planetary system to which the Earth Belongs. It was formed about 5.000 million years ago. It consists of eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune) and another celestial bodies (asteroids, satellites and comets) which move around a star of average size, the Sun.

Location of the Solar System in the Milky Way.

The Solar System.

Star size comparision HD

Why the Earth is a living planet?

The Earth is the only planet in the Solar System, and the only known planet, where there is life. Life appeared in Earth about 2.000 million years ago. There are three characteristics that explain this:

1. Abundant supply of liquid water, in the form of oceans and seas. Because of this, it is called the Blue Planet.

The Earth, the Blue Planet.

2. Moderate temperature., it is not too hot (like Venus) or cold (like Mars). It is located about the right distance from the Sun (around 150 million kilometres).

3. The atmosphere, because:

-Contains gases which are essential for life, such as oxygen.

-The atmosphere protects the Earth from dangerous solar radiation.

The Atmosphere as a protective layer.

The Earth: characteristics.

It was formed 4.600 million years ago. Its main characteristics are:

Its an imperfect sphere (geoid), wider at the Equator than at the Poles.

Its surface is 510 million km2, a thousand times the area of Spain. 

Most of its surface is covered by oceans and seas.

Can be divided in two equal parts across the Equator.