xkcd.WTF!?

Explanation ➲

This comic is a play on the Messier Catalog, which is a famous list of astronomical objects "that are not a comet" compiled by the French astronomer Charles Messier in the 18th century. The real Messier Catalog includes 110 objects, which are all deep-space objects like nebulae and galaxies.

In the comic, it's humorously suggested that the catalog includes not just these distant celestial objects, but also very ordinary things found here on Earth. Each ordinary object is labeled with an "M" followed by a number, just as the real Messier objects are numbered (like M1, M2, etc.). However, the numbers are much higher than the 110 included in the actual catalog, and they point to mundane things such as the Earth, Charles Messier himself, a tree, a butterfly and a squirrel.

The numbers increase as the objects go from large and significant to humans (the Earth, Charles Messier) to those that are smaller and less significant (a tree, a butterfly, and a squirrel). However, this pattern isn't strictly numerical (i.e., there's no clear mathematical sequence), but rather a conceptual one where the numbers arbitrarily become larger for things that are commonly considered less monumental or noteworthy than celestial objects.

So, the comic is a playful take on a piece of astronomical history, suggesting that everything in the universe is part of the Messier Catalog, not just the deep sky objects Messier originally listed.

The title text refers to the Ship of Theseus. This is a popular thought experiment: if a ship is repaired and/or modified such that it has all of its parts replaced over the years, is it the same ship as the original? And then, what if you take all of the parts that were removed and create another ship using those parts? Are they both the same ship, and if not, which one is the original ship? The title text suggests that this leads to a debate as to whether the original ship and the new ship (with all of its parts replaced) should be considered the same object and therefore given the same Messier number, or the two ships should be considered different objects with different Messier numbers, and if so, which of them should retain the original number.

"M41592" may be a reference to pi as it contains 5 of the first digits at 3.141592. Also noteworthy is that (the real) M6 is called the Butterfly Cluster. However, there are no real galaxies in the original Messier Catalog named after trees or squirrels.

"M137" for Earth seems likely to be a reference to the animated sci-fi/comedy show Rick and Morty, since the version of Rick primarily followed by the show comes from Dimension C-137, even identifying himself as Rick C-137 when around Ricks and Mortys from other dimensions.