International Astronomical Union

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Introduction References & Edit History Quick Facts & Related Topics

Videos

How do features on Pluto and its moons get their names?

Why isn't Pluto a planet?

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Remarkable new details of Pluto's largest moon Charon are revealed in this image from New Horizons' Long Range Reconnaissance Imager (LORRI), taken late on July 13, 2015 from a distance of 289,000 miles

Why Is Pluto No Longer a Planet?

Planet Earth and lunar moon from space

Where Did the Moon Come From?

solar eclipse, sun, moon, astronomy, space

How Do You Tell the Difference Between Total, Annular, Solar, and Lunar Eclipses?

Arrangement of the phases of the moon in total eclipse with Blood Moon

9 Celestial Omens

1 July 2002: The Solar and Heliospheric Observatory (SOHO) satellite reveals a massive solar eruption more than 30 times the Earth's diameter. The eruption formed when a loop of a magnetic field over the surface of the Sun trapped hot gas.

6 Questions About the Sun Answered

Discover

Nelson Mandela, undated photo.

15 Nelson Mandela Quotes

African Americans demonstrating for voting rights in front of the White House as police and others watch, March 12, 1965. One sign reads, "We demand the right to vote everywhere." Voting Rights Act, civil rights.

Timeline of the American Civil Rights Movement

Middle East bee locator map

Are the Middle East and the Near East the Same Thing?

Scolex (head) of the tapeworm Taenia solium. The hooks of the scolex enable the tapeworm to attach to the intestinal wall.

Uninvited Guests: The 7 Worst Parasitic Worms

Lake Mead (the impounded Colorado River) at the Hoover Dam. The light-coloured band of rock above the shoreline shows the decrease in water level in the first few years of the 21st century.

6 Lakes That Are Drying Up

Paul Revere. "The bloody massacre perpetrated in King Street Boston on March 5th 1770 by a party of the 29th Regt.," engraved by Paul Revere. Boston Massacre.

There’s a Riot Goin’ On: Riots in U.S. History (Part One)

Dancers at a Cinco de Mayo festival at the Mission District, San Francisco, California. (Photo dated 2019.) holidays

Is Cinco de Mayo Mexico's Independence Day?

International Astronomical Union: Facts & Related Content

Written and fact-checked by The Information Architects of Encyclopaedia Britannica

Last Updated: May 25, 2025

News •

New minor planet found in the distant solar system • May 23, 2025, 3:48 AM ET (EarthSky)

Facts

Also Known As	IAU
Date	1919 - present
Headquarters	Paris
Areas Of Involvement	astronomy
Related People	Arthur Eddington

Videos

How do features on Pluto and its moons get their names?

Why isn't Pluto a planet?

See All Videos →

Topics

European Union United Nations North Atlantic Treaty Organization OPEC Commonwealth World Health Organization League of Nations World Trade Organization United Nations Security Council ASEAN

Demystified

Remarkable new details of Pluto's largest moon Charon are revealed in this image from New Horizons' Long Range Reconnaissance Imager (LORRI), taken late on July 13, 2015 from a distance of 289,000 miles

Why Is Pluto No Longer a Planet?