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.

Lagoon Nebula (cc: NASA).

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.

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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.

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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.

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Vocabulary Building

The following is a recommended list of words and their definitions for students.

Big Bang: the explosion of a ball of matter and energy that created the known universe

galaxy: a large system of stars, gas, and dust held together by gravity.

nebula: is a cloud of gas and dust in space.

star: a very large ball of burning gas in space such as the sun.

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.

• What is the Big Bang?

• What is the largest object in the universe?

• What is a nebula?



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