Universe

Introduction
Earliest conceptions of the universe
Astronomical theories of the ancient Greeks
The system of Aristotle and its impact on medieval thought
The Copernican revolution
Perceptions of the 20th century
- Kapteyn’s statistical studies
- Shapley’s contributions
- Hubble’s research on extragalactic systems

References & Edit History Related Topics

Images & Videos

Britannica editor Erik Gregersen, a white man wearing glasses, holds a microphone in front of a galaxy background. Displayed above him are the phrases: Ask an Editor, and How old is the universe?

Diagram of the Milky Way galaxy showing labeled locations of the Sun, Milky Way center, Sagittarius dwarf elliptical, and Canis Major dwarf, with axes marking 80,000 light-years.

How did Ptolemy explain retrograde motion?

Diagram illustrating Eratosthenes' method for calculating Earth's circumference, showing the angle of sunlight at Syene and Alexandria, camels traveling between the two cities, and rays from the Sun striking Earth's surface at different angles.

Aristotle's theory of the solar system explained

Copernicus's revolutionary theory: The Sun as the center

Kepler's revolutionary laws of planetary motion

At a Glance

universe summary

Quizzes

View of the Andromeda Galaxy (Messier 31, M31).

Astronomy and Space Quiz

The orbits of the planets and other elements of the solar system, including asteroids, Kuiper belt, Oort cloud, comet

Space Odyssey

Ursa major constellation illustration art. (Big Dipper) stars, space, night sky)

Stars: Explosions in Space

Nicolaus Copernicus. Nicolas Copernicus (1473-1543) Polish astronomer. In 1543 he published, forward proof of a Heliocentric (sun centered) universe. Coloured stipple engraving published London 1802. De revolutionibus orbium coelestium libri vi.

All About Astronomy

Related Questions

How did Edwin Hubble provide evidence for an expanding universe?
How did primordial nucleosynthesis produce helium in the early universe?
How did small cosmic microwave background fluctuations help galaxies form?
How did the cosmic microwave background form when the early universe became transparent?
How did the steady-state theory explain an expanding universe?
How did the universe change as it expanded and cooled after the big bang?
How does gravitational lensing reveal dark matter in galaxies and galaxy clusters?
How does weak gravitational lensing help astronomers study dark energy?
How have the Hubble Space Telescope and James Webb Space Telescope helped astronomers study early galaxies?
How was the cosmic microwave background discovered by Arno Penzias and Robert Wilson?
What are the possible long-term outcomes for the universe according to cosmology?
What did WMAP measurements reveal about the early universe?
What did the COBE satellite discover about tiny fluctuations in the cosmic microwave background?
What does Hubble’s law say about the distance and recession speed of galaxies?
What role did Georges Lemaître play in developing the big-bang theory?
What types of telescopes help astronomers observe the distant universe?
When did the first stars and galaxies begin to form?
Why did distant radio galaxies challenge the steady-state theory?
Why do the observed amounts of hydrogen, helium, and deuterium support the big-bang model?
Why does looking at distant galaxies reveal the universe’s past?
Why is the cosmic microwave background considered evidence for the big bang?
Why is the cosmic microwave background only about 2.7 kelvins today?
Why were distant Type Ia supernovas fainter than expected in a universe without dark energy?
What is solar energy?
How is solar energy collected?
What are the advantages and disadvantages of solar energy?
How is a black hole formed?
What are some examples of black holes?
What are the types of dark matter?
What are constellations?
How many constellations are officially recognized?
How many planets are in the solar system?
How did the solar system form?

Science Astronomy

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External Websites

NASA Science - What is the universe?
Salt Lake Community College Pressbooks - Physical Geography and Natural Disasters - The Universe
LiveScience - How Did the Universe Begin?

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

universe - Children's Encyclopedia (Ages 8-11)
universe - Student Encyclopedia (Ages 11 and up)

Universe

astronomy

Written by

Frank H. Shu

Professor of Physics, University of Calfornia, San Diego. Author of The Physical Universe.

Frank H. Shu

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 12, 2026 •History

Universe, the whole cosmic system of matter and energy of which Earth, and therefore the human race, is a part. Humanity has traveled a long road since societies imagined Earth, the Sun, and the Moon as the main objects of creation, with the rest of the universe being formed almost as an afterthought. Today it is known that Earth is only a small ball of rock in a space of unimaginable vastness and that the...

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