The universe is everything that exists in space. This includes the galaxies, stars, solar systems, and planets. The universe was created 13.8 billion years ago in the Big Bang. This event created all of the matter and energy in space.
Image: the Lagoon Nebula is a region of gases where stars are made (Creative Commons: NASA).
Birth of the Universe
The universe is thought to have been created by the Big Bang. This was a huge explosion that released all the matter and energy into existence. The Big Bang occurred about 13.8 billion years ago.
As the matter cooled, it condensed into nebulae. Nebulae are huge clouds of gas and dust. Eventually, the force of gravity pulled these clouds together into smaller balls. These balls would become galaxies, nebula, stars, solar systems, and planets.
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 in one of many such systems in the Milky Way galaxy. As many as two trillion galaxies may exist.
There are three basic types of galaxies. These are the elliptical, irregular, and spiral galaxies. The earth is found in the spiral Milky Way galaxy. Each galaxy is composed of billions of stars.
- Galaxy: the Largest Object in the Universe
- Elliptical Galaxy: the Old Galaxy
- Irregular Galaxy: Galaxies in Collision
- Spiral Galaxy: Young at Heart
- Milky Way: Living in the Spiral Arms
Stars and Other Objects
Stars go through a life cycle. They are born, they mature, and then they die. Not every star goes through the same life cycle. Stars may become dwarf stars or become supernovae at the end of their life.
- Life Cycle of Stars: From Ashes to Dust
- Nebula: Star Cooking with Gas
- Supernova: Going Out with a Bang
The following is a recommended list of words and their definitions for students.
Improving Your Reading and Thinking Skills
Think for a few moments. Try to recall the major ideas in this article. Try to answer the following questions to improve your reading comprehension.
- Our Expanding Universe, Space.com.