What is the International Astronomical Union (IAU)?

Mary McMahon
Mary McMahon

The International Astronomical Union (IAU) is an organization which coordinates the work of national astronomy associations along with professional astronomers. The IAU promotes advancement in the science of astronomy, along with protection of astronomy as a scientific field. It is a member organization of the International Council for Science, a group of international scientific organizations which includes the International Union of Pure and Applied Chemistry and the International Mathematical Union, among many others.

A galaxy.
A galaxy.

This organization was founded in 1919 with the melding of several astronomy organizations. It is based in Paris, France, and includes individual professional members, most of whom are leaders in the field of astronomy, along with numerous national astronomy organizations. While the bulk of the International Astronomical Union's work is focused on advancements in professional astronomy, the organization also works with groups which include amateur astronomers among their members, and it recognizes the valuable contributions made by some amateur astronomers.

A meteor and a radio telescope.
A meteor and a radio telescope.

One of the key aspects of the work of the International Astronomical Union is the development of uniform and consistent terminology through the Working Group for Planetary System Nomenclature. The organization has extensively defined and designated terms for use in astronomy so that astronomers can clearly communicate with each other. When an astronomer writes about a “planet” in a scientific paper, for example, other astronomers know precisely what sort of celestial body that astronomer is referring to, thanks to the standards set by the IAU.

There are several parts to the IAU. The first is the General Assembly, a collective of the representative member nations which meets every three years to set policy. The locations of General Assembly meetings rotate, giving every member nation an opportunity to host the International Astronomical Union. The organization as a whole is broken into divisions, with each division subdivided into commissions. The commissions in turn have a large pool of working groups and programs which work on individual issues.

For reasons of standardization, astronomy texts usually stick with terminology which has been defined by the International Astronomical Union, and the organization publishes updates periodically so that people in the field can keep up with changing terminology. The definitions published by the IAU are not without controversy, however, as scientists are a notoriously stickling and argumentative bunch, and astronomers are no exception. The decision to downgrade Pluto from a "planet" to a "dwarf planet" and later a "plutoid," for example, attracted a great deal of attention.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@Charred - Yes, anytime you have assemblies, there will be a uniquely political nature to the kind of work you do. The International Astronomical Union Symposium is no exception.

People deliberate, they disagree, they vote. It’s the nature of the beast. I don’t think definitions are as important as scientific experiments personally.

But since we are moving towards a global society I can see why the work of the symposium is important.


@SkyWhisperer - Standards are important. I am glad the organization exists to establish those standards. Anytime you establish standards, however, you will run into controversy from time to time.

We have the metric system, for example. This is an international standard, yet the United States is still lax to implement the metric system. I figure we’ll catch up in a few more decades.

Still, it doesn’t make sense to make the rest of the world stick with the old English system, does it? The metric system makes more sense in my opinion.

In the final analysis, whatever standards you set forth, you must be able to defend them, and consistency is a big requirement. If the changes bother you that much, just read your old astronomy books, written before the latest discoveries.


@SkyWhisperer - I don’t think it was by fiat actually. They found another planet further out than Pluto. This other planet was larger than Pluto yet it was called a “dwarf planet.”

I don’t know all the criteria for calling a planet a dwarf planet. However, the astronomic society was faced with a problem. If the last planet, bigger than Pluto, was a dwarf planet, why was Pluto a planet?

I think in the end it came down to consistency. So they had to redefine Pluto as a dwarf planet. It’s still part of the solar system, but it doesn’t really hold its own, so to speak, like the other planets do.

I don’t think there was an agenda driving the decision. Science is a process of discovery. Sometimes you need to redefine your assumptions based on new data.


Where did the astronomical society get the nerve to downgrade Pluto from a planet to a dwarf planet? When that happened, they were held up to all sorts of ridicule in the press.

Sometimes I wonder if there is a hidden agenda driving this decision making. But people, let’s be serious. Pluto was never a threat to anybody’s astronomical worldview. It’s so far out there, and its discovery was heralded as a great achievement and a welcome addition to the solar system.

Now it’s been shown the back door so to speak, because the society decided, almost by fiat, to redefine what it means to be a planet.

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