The universe contain galaxies, stars, black holes, planets, comets and meteors. In short, it holds all matter and energy. It also has a lot of empty space. It has around 80 billion galaxies or many large group of stars. The Sun is just one of the many stars in the universe. There are also many planets orbiting these stars. The size of the universe is still unknown.
Scientists believe that the universe continues to expand outwards. The galaxies are also moving apart. With the universe existing space, matter and time also came into existence. No one knows the exact size of the universe.
The famous Big Bang theory explains the origin of the universe. It is a cosmic cataclysm which took place almost 14 billion years ago. Georges Lemaître, a Belgian priest, first suggested this theory in 1920. To this day scientists continue to study what started the Big Bang. There is no instrument that can give specific details on how it all started, but with the use of mathematical theories, models, and the cosmic microwave background, they understand the origin and expansion of the universe.
Several space missions where made by NASA and other organizations to study the CMB. Their study of the CMB gave them clues on what the universe contains. As a result, they learned that the universe is composed only of 5 percent matter including all the galaxies, stars, planets, comets and meteors.