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Astronomy for Kids

The Universe

Pillars of Creation by the Hubble Space Telescope
The "Pillars of Creation"
Photo by the Hubble Space Telescope.
Source: NASA.
What is the universe?

The universe contains everything that exists including the Earth, planets, stars, space, and galaxies. This includes all matter, energy, and even time.

How big is the universe?

No one knows for sure just how big the universe is. It could be infinitely large. Scientists, however, measure the size of the universe by what they can see. They call this the "observable universe." The observable universe is around 93 billion light years across.

The Universe is Expanding

One of the interesting things about the universe is that it is currently expanding. It's growing larger and larger all the time. Not only is it growing larger, but the edge of the universe is expanding at a faster and faster rate. Scientists think that the edge of the universe is expanding faster than the speed of light.

Timeline of the universe expansion
Timeline of the Universe over 13.77 billion years.
Scientists think it is still expanding at a very fast rate.
Source: NASA.

What is the universe made of?

Even though the Earth seems really big to us, it's actually a very tiny part of the universe. The Sun has a mass of 330,000 times the Earth. The Sun is just one star in the Milky Way galaxy that contains over 300 billion stars and scientists estimate that there are over 170 billion galaxies in the universe!

However, most of the universe is what we think of as empty space. All the atoms together only make up around four percent of the universe. The majority of the universe consists of something scientists call dark matter and dark energy.

What are dark matter and dark energy?

We mentioned above that the majority of the universe is made up of dark matter and dark energy, but what exactly are these things? How old is the universe?

Scientists think that the universe began between 13 and 14 billion years ago with the start of a massive explosion called the Big Bang.

Shapes of the universe
The shape of the universe may be
closed (top), open (middle), or flat (bottom).
Source: NASA.
Interesting Facts about the Universe

More Astronomy Subjects

The Sun and Planets
Solar System

Black Holes
Meteors and Comets
Sunspots and Solar Wind
Solar and Lunar Eclipse

Space Exploration Timeline
Space Race
Nuclear Fusion
Astronomy Glossary

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