Before setting out to conquer space, let’s get to know our solar system.
THE SUN :

The sun is a star at the center of our solar system. In stars, hydrogen and helium atoms undergo nuclear fusion reaction to produce new atome. The reactions release phenomenal amounts of energy in the form of light, making stars primary sources of light.
The sun is located 150 million km from the Earth.
THE EARTH :

The Earth revolves around the sun in an almost circular trajectory ( orbital)
It orbits the sun in 364.25 days. This time is called the period of revolution.
The Earth turns on itself in 24 hours.
This time is called the rotation period.
THE MOON: 

The Moon revolves around the Earth in 29.5 days. This time is called its period of revolution around the Earth, and the Moon’s path is almost circular.
The Moon is a natural satellite of the Earth.
A satellite is an object that orbits ( gravitates) around certain planets.
The Moon rotates on itself. It period of rotation is almost equal to its period of revolution around the Earth.
The phases of the Moon correspond to the different aspects of the Moon ( seen from the Earth) during its revolution around the Earth.
THE SOLAR SYSTEM :

Our solar system appeared 4.5 billion years ago in a cloud of gas and dust. This cloud of gas concentrated to give birth to our Sun, then to our 8 planets, to the dwarf planets ( Pluto…), to the asteroids and to the comets ( large blocks of ice)
The different celestial objects are attracted by the sun but do not fall on it.
The solar system is located within a group of several hundred billion stars called a galaxy. Our galaxy, the Milky Way

, is shaped like a spiral, rotating on itself.

The planets in our solar system can be divided into two groups.
-> The telluric planets ( which have a rocky soil). The are small.
There is Mercury, Venus, Earth and Mars, the red planet.

-> The gaseous planets ( balls of gas)
They are bigger. There is Jupiter, Saturn, Uranus and Neptune.

The two families of planets are separated by an asteroid belt ( large non-spherical rocks)
The periphery of the solar system is made up of a belt of small icy bodies and dust called the KUIPER belt.
The last objects in our solar system are the natural satellites.
A satellite is a spherical celestial body that orbits a planet. A planet can have one( Earth) or several ( Mars , Jupiter…) satellites.

These objects are attracted to their planet but they do not fall on it because they orbit their planet at the right speed.

The representation on the scale of the solar system are impossible to carry out because of the distances and de dimensions considered.
Note: planets orbiting a star other than our sun 

 (i.e. outside our solar system ) are called exo planets.

THE UNITS OF DISTANCE IN ASTRONOMY :
The distance between celestial bodies and their dimensions are considerable !
The unit of kilometers is far to small.
That’s why in astronomy we use two other units.
-> The astronomical unit :
It corresponds to the distance between the Earth and the Sun, that is 150 million km. This unit is used to talk about distances in our solar system .
The size of the solar system is 100au.
-> The light year :
It corresponds to the distance traveled in 1 year by light ( knowing that it moves at a speed of 300,000km in 1 second). This unit is used to express the distances between stars or between galaxies.
For example the star, outside our solar system, the closest to the Earth is PROXIMA CENTAURI and it is 4.2al from Earth.

And now let’s go on our fabulous adventure….