Mercury A to Z: International Astronomical Union

Hello, friends!  The planet Mercury doesn’t get nearly as much love and attention as he deserves, which is why I picked Mercury as my theme for this year’s A to Z Challenge.  In today’s post, I is for:


The International Astronomical Union (I.A.U.) has the awesome responsibility of naming astronomical objects and defining important astronomical terminology.  The I.A.U. is probably most famous (or infamous) for their 2006 decision to change the definition of the word planet in such a way as to exclude Pluto from the planet club.  But we’re not going to talk about that today.  Instead, I want to tell you about one of my favorite Mercury fun facts.  According to I.A.U. rules, all craters on Mercury are supposed to be named after artists, musicians, and writers.

Apparently the I.A.U. was originally planning to name Mercury’s craters either after birds or cities.  It was Carl Sagan, always one for blending the sciences with the humanities, who lobbied for naming the craters on Mercury after poets and authors.  The I.A.U. ultimately went with Sagan’s idea, expanding it to include musicians, painters, sculptors, etc.

Some craters did have well established names before the I.A.U. made that rule, so Caloris Basin (named after the Latin word for heat) and Kuiper Crater (which we’ll visit in just a few days) are exceptions to the rule.  But otherwise, the I.A.U. has been consistent about following their naming convention.  There’s a Shakespeare Crater, a Beethoven Crater, a Mark Twain Crater… there are craters named after John Lennon and Chuck Berry… craters named after J.R.R. Tolkien and H.P. Lovecraft….  Maya Angelou has a crater.  Dr. Seuss has a crater.  There’s even a crater named after Walt Disney (and if you’ve never seen a picture of Disney Crater, you need to see a picture of Disney Crater).

So if you would like to have a crater on Mercury named after you, the I.A.U. says you only have to meet two criteria:

  • Be famous or be considered historically significant as a writer, artist, or musician for more than fifty years, and…
  • Be dead for at least three years.

The I.A.U. also tries to avoid using names that are too heavily associated with politics, the military, or religion.  So try to avoid getting too tangled up in those things during your lifetime.


Curious to see if your favorite artist, writer, or musician has a crater on Mercury?  Here’s a list of named craters on Mercury.

Wondering how the I.A.U. names things other than craters on Mercury?  Here’s a list of official themes the I.A.U. uses for naming surface features on the various planets and moons of the Solar System.

Lastly, I know I recommended this book before, but I’m going to recommend Mercury, by William Sheehan, once again.  It’s part of the Kosmos series.  That’s where I learned about Carl Sagan’s role in coming up with the I.A.U.’s Mercurian crater naming convention.

6 thoughts on “Mercury A to Z: International Astronomical Union

    1. I think it’s only the largest of the three craters that’s officially named Disney crater. The two “ears” are different craters. I’m not sure if they’ve been named yet.


  1. Mercury is my favorite planet, and I’ve added the book to my wish list. I always enjoy Reaktion books, and I’m sure this one will also delight. I love Sagan’s idea. I’ll be amusing myself coming up with my own list of crater names, whether they’re IAU sanctioned or not.

    Liked by 1 person

    1. If you’re a Mercury fan, you’ll love that book. It’s a rare thing to find a book about one specific planet, unless that planet is Mars. And the Kosmos series is so well researched and so well presented.

      Mercury is the most heavily cratered object in the whole Solar System, so the I.A.U. has left plenty of craters to be named.

      Liked by 1 person

    1. Which book? The one by Neil deGrasse Tyson book or the “Why I Killed Pluto” book? I actually haven’t read either one yet. Instead, I read a book by Alan Stern (NASA scientist on the New Horizons Mission) where he argued the I.A.U. got it wrong and Pluto is still a planet.


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