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NASA's Space Place

The Amazing Universe

By Linda Hermans-Killam
National Aeronautics and Space Administration

"The cosmos is all that is, or ever was, or ever will be." This is how astronomer Carl Sagan described the universe. Cosmos is another word for universe. The universe is made up of everything we know of. Earth, the sun, and the moon are part of the universe. In fact, so are all of the planets, stars, and galaxies. All of space, time, energy, and matter exist inside the universe. The universe is so big that we cannot even see it all, and never will!

But where did the universe come from? Scientists who study the universe are called astronomers. Astronomers discovered evidence that the universe was created in an enormous expansion beginning about 13.8 billion years ago called the Big Bang. At that moment, all of the matter and energy in the universe was created. Time and space were also created in the Big Bang.

At the time of the Big Bang, everything in the universe was squeezed together in an incredibly hot and compressed state. The heat and pressure caused the universe to expand at extremely high speeds, which created space. As the universe expanded and cooled, stars, planets, and galaxies formed out of the matter present at the Big Bang. Today, the universe contains billions of galaxies, each of which contain millions or billions of stars, and possibly millions or billions of planets and moons.

But all of the things that we can see in the universe—such as planets, stars, and galaxies—make up only about 5 percent of what is in the universe. Most of the universe is made up of mysterious forms of matter and energy that we cannot see. These forms of matter and energy are called dark matter and dark energy.

We do not yet understand what dark energy and dark matter are. However, experiments show that they exist. Dark matter is thought to make up about 27 percent of the universe, while about 68 percent of the universe is thought to be dark energy. Dark matter clumps together similar to the way galaxies do. Dark energy is thought to fill all of space, maybe the same everywhere, but maybe different at different places and times.

So as you can see, the universe is a huge, amazing place with many exciting mysteries to solve and discoveries to be made!

If you want to learn more about the Big Bang, visit the NASA Space Place: http://spaceplace.nasa.gov/big-bang/en/

Hubble Space Telescope image of a small part of the universe filled with galaxies. It would take around 25 million pictures like this to cover the whole sky – space is really big!

Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)


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