8. The universe and the Earth


This unit looks at the universe and the characteristics of planet Earth, as well as its satellite, the Moon. You should have an overall picture of the universe and should understand the importance of studying it as a means of understanding the origin and evolution of the planet on which we live.


The universe is made up of collections of celestial bodies (planets, satellites, stars), in addition to gases and dust, which make up galaxies.

The solar system is also made up of a star, the Sun, around which the planets and their satellites revolve.

Which is the relationship between the movements of the Earth and the existence of day and night or the change of seasons?
Earth rotates on its axis and revolves around the sun in its orbit. Rotation gives it day/night, while earth is tilted on its axis, revolution gives it seasons.


What is the universe?

The concept of the universe has changed a lot throughout history. The Greeks used observations and measurements and concluded that the Earth is a spherical body which floats in space with other celestial bodies. This resulted in other scientific theories such as geocentrism and heliocentrism.

The current concept of the universe

The Universe is a collection of all the matter, energy and time that exists, and that it occupies an enormous space.
Most of the universe is empty or contains dark matter that is very difficult to detect. The rest of the matter is concentrated in galaxies. Galaxies are immense collections of thousands of millions of stars and nebulas, or areas of gas and dust that come from the stars.
Stars are enormous spheres of matter that emit energy (mostly light and heat) and high-speed particles (stellar wind), due to the nuclear reactions that take place inside them.
Structure of Universe. At the end it shows the Milky Way galaxy
Many of the stars have different types of celestial bodies around them (planets, satellites, asteroids, comets, etc.). These collections of celestial bodies are known as solar systems. Our planet, the Earth, is in a solar system.

2.Our solar system

The solar system is located in the Milky Way galaxy, which is part of a cluster of about twenty galaxies known as a Local Group.
Resultado de imagen de milky way galaxy gif
If you could travel outside the galaxy and look down on it from above, you’d see that the Milky Way is a spiral galaxy. It seems to have two spiral arms. The Solar System is located in a region between the two arms.

The Sun

The Sun is a yellow star that is small sized when compared to other stars. It moves through space with the rotation of the galaxy.
Resultado de imagen de the sun rotation gif
The Sun also rotates on its own axis. Like other stars, the Sun sends energy out into space in the form of light and heat, as well as a stellar wind of particles. This wind is called the solar wind.
Scientists have calculated that the Sun was created 5 000 million years ago and they believe it will continue to emit energy for another 4 500 million years.

The planets

The planets in our solar system travel in elliptical orbits around the Sun and at different distances from it.
Imagen relacionada
In the solar system there are also two types of planets:
The rocky or inner planets. These are Mercury, Venus, Earth and Mars. They are small and made mostly of rock.
The gas or outer planets. These are Jupiter, Saturn, Uranus and Neptune. They are much larger that the rocky planets. They have a small solid nucleus and a large atmosphere. All of them have rings around them.

The satellites

Satellites orbit planets. All the planets in the solar system, apart from Mercury and Venus, have one or more satellites.
There are 79 known moons of Jupiter. This gives Jupiter the largest number of moons of any planet in the Solar System.
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