The term universe means the world as we know it. In other words, the term universe encompasses space and all substances and energy contained inside it. According to our modern understanding, the universe was formed 14 billion years ago as a result of a gigantic explosion ("the Big Bang") and the rapid expansion that followed it.

After a while, the gases that were created during the explosion began to concentrate, forming star systems or galaxies. There are millions of galaxies in the universe. They are like small islands dotted across the infinite, empty sea of space.

Our own galaxy is called the Milky Way. It consists of 100–400 billion stars. Its diameter is approximately 100 000 light years long, and it is over 10 000 light years wide. 

The light year is a unit of distance that is widely used in astronomy. A light year represents the distance that light travels during a single year. This means that a single light year is an incomprehensibly long distance. Light travels at a speed of approximately 300 000 kilometers per second, meaning that the distance from the Earth to the Moon takes light only just over one second to travel. The distance between the Sun and the Earth takes light approximately eight minutes, whereas the distance between Earth and the next solar system takes four light years to travel.