The Universe

  • About

    • The observable universe contains as many as 100 billion galaxies and extends a billion light-years in every direction.

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  • For Educators

    • Topic: Astronomy

      Subtopic: Universe

      Keywords: Universe, Light--Speed, Galaxies

      Audience: General

In This Section

Formation and Evolution of the Universe

Formation and Evolution of the Universe

Our Milky Way Galaxy was once thought to comprise the entire known universe. Today our universe encompasses many billions of galaxies, and its history can be recounted back to its earliest moments.

Dimming Starlight

Dimming Starlight

Telescopes can easily zoom in on a star. But to see a dim object next to a star, such as a planet, astronomers need to block out the star’s light.

What is the Universe?

What is the Universe?

The universe is all the matter, energy, and space that exist. We can observe only a part of it - the observable universe. 

The Big Bang

The Big Bang

The Big Bang is the scientific description of the origin of the cosmos.

Evolution of the Universe

Evolution of the Universe

Galaxies form and evolve within an expanding and cooling universe. Because light takes billions of years to cross the cosmos, we see distant galaxies as they were at earlier times.