The universe is everything that exists in space. This includes galaxies, stars, solar systems, and planets. The universe was created 13.8 billion years ago. All of the matter and energy in space was created in one gigantic Big Bang.
Birth of the Universe
Science believes that the universe was created by the Big Bang. This was a huge explosion that released all the matter and energy that now exists. Evidence suggests that this Big Bang took place 13.8 billion years ago.
As the matter from the Big Bang cooled, it began to condense into nebulae. Nebulae are huge clouds of gas and dust. Eventually, the force of gravity pulled the cloud particles together into balls of dust and gas. These balls would continue to condense and form galaxies, stars, star systems, and planets.
The universe is made up of ordinary matter. However, this only accounts for about 5% of all the matter that exists. As a result, scientists have hypothesized that “dark matter” makes up the rest of the universe. Dark matter may be responsible for the ongoing expansion of the universe.
Galaxies
The largest objects in the universe are galaxies. A galaxy is a cluster of stars, dust and gas held together by gravity. The Earth’s solar system is one of many star systems in the Milky Way galaxy. As many as two trillion other galaxies may exist.
There are three basic types of galaxies. These are the elliptical, irregular, and spiral galaxies. The earth is found in the Milky Way which is a spiral galaxy. Each such galaxy is composed of billions of stars.
Stars and Other Celestial Objects
Stars go through a life cycle. They are born, they mature, and then they die. However, stars do not all have the same life cycle. Some stars become dwarf stars and others become supernovae at the end of their life.
Stars may be the center of their own star systems. The solar system is a star system made up of a sun and eight planets. Other celestial bodies within the solar system include satellites, asteroids, and comets.
Reflections
Vocabulary
- Big Bang
- galaxy
- nebula
Notes
- The Big Bang created the universe 13.8 billion years ago.
- Galaxies are the largest objects in the universe and exist as three basic types.
- There are billions of stars and star systems in each galaxy.
Bibliography
- A Universe Study Guide
- Our Expanding Universe, Space.com.
