The International Astronomical Union celebrates its 100th anniversary

First General Assembly of the IAU in Rome, Italy, in 1922
Credit: UAI
Première assemblée générale de l’UAI à Rome, Italie, en 1922
  • Première assemblée générale de l’UAI à Rome, Italie, en 1922
  • Logo de l’Union astronomique internationale
  • Vote lors de l’assemblée générale de 2006 à Prague, République tchèque, entérinant le statut de planète naine à Pluton
The International Astronomical Union celebrates its 100th anniversary

In July 2019, the International Astronomical Union (IAU) marked the centennial of its founding. After modest beginnings, the organization grew to become the international authority in astronomy, and now consists of over 13,500 members hailing from 96 countries around the world.

A humble birth

In 1919, the First World War had just ended and the world was licking its wounds. At the time, American astronomer George Ellery Hale had been working on the creation of an international science and research organization, and in its wake, the International Astronomical Union was created on July 26, 1919. It’s now headquartered at the Institut d’astrophysique de Paris.

The goal of the IAU is to coordinate the work of astronomers from all over the world. Members of the organization get together every three years in a general assembly. The first assembly took place in Rome in 1922. It’s been held just once in Canada, when Montréal hosted the august institution’s discussions in 1979.

IAU activities are overseen by 40 commissions touching on every area of astronomy. In recent times it’s attached great importance to education and the dissemination of astronomical knowledge to the public.

Naming the celestial bodies

One of the important roles of the IAU is defining the rules governing the nomenclature of celestial objects. As such, it’s the only organization entitled to provide them with names.

Incidentally, it was at that first assembly in 1922 that the number, boundaries and names of the constellations that we use today were defined.

Since that time, precise rules have been established for the naming of stars, planets, planet satellites or structures on their surface, asteroids or comets, and dwarf planets.

You have to be careful of anyone who proposes naming a star in your name or the name of a loved one, especially in exchange for money. That would be fraudulent, because none of those names would be recognized by the IAU. Bear in mind that the IAU authorizes no one to sell the names of heavenly bodies. On top of that, the same star could be sold a number of times or by different organizations!

Pluto’s no longer a planet

In 2006 the IAU made headlines when its members, gathered in Prague, adopted a new, more precise definition of a planet. The effect was that Pluto got relegated to the status of dwarf planet. Pluto’s now considered the prototype of trans-Neptunian objects, meaning the bodies orbiting the Sun at a greater distance than the planet Neptune.

In the course of this first century of the organization’s history there’ve been numerous upheavals in astronomy: the expansion of the Universe, the discovery of asteroids, of dwarf planets and of exoplanets, the nature of galaxies, and many others. And each time the IAU has been at the heart of these events or discoveries. Long live the International Astronomical Union!

Definitions of a planet and a dwarf planet

A planet is a body:

  • orbiting around a star,
  • massive enough to take on an almost round shape,
  • that has cleared its orbit of all other bodies.

A dwarf planet is a body:

  • that is not a satellite of a planet,
  • orbiting around a star,
  • massive enough to take on an almost round shape,
  • that has not cleared its orbit of all other bodies.

For more information on observing planets, constellations, and other astronomical phenomena
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