xkcd.WTF!?

Explanation ➲

The comic shows two overlapping circles. This is a simple example of a Venn Diagram, which is a way that set theorists often illustrate the relationships between sets. Venn diagrams can consist of a number of overlapping shapes to describe the similarities and differences between any number of objects. Up to three overlapping circles can be used to represent every combination of membership of those separate sets. Beyond this, circles cannot suffice and other shapes (ovals or even concave shapes) are needed, but just two such areas is as trivial as shown, with the portion of the diagram where the two circles overlap represents the intersection of the sets (items that are in both sets). There are several other comics about Venn diagrams.

The two sets in this diagram are set theorists and astronomers. Set theorists would find the shape here interesting because such diagrams would appear regularly in their work. Astronomers also find overlapping circles interesting, because this is what they see during eclipses, when one astronomical body is directly or partially in front of another. In the overlapping section in the middle would be people who are both set theorists and astronomers. The joke here is that these people would be particularly excited by the shape, because it represents the overlapping of both their fields of study.

Note that Randall seems to have chosen humor over scientific accuracy. Read literally, this diagram appears to be saying that the only people who are excited about the shape are those who are both set theorists and astronomers. The label that is in the intersection of the two circles should properly apply to their union. However, a pedantic person might note that the label is actually within the union of the two circles, so perhaps all is well after all.

A common snarky comment on the Internet is "The Venn diagram of [x] and [y] is a circle" (for example, "xkcd" and "peak fiction"), implying that the two sets are identical. Totality describes a total (full) eclipse, when one astronomical body completely blocks the light from another. During totality, the shape of the eclipse is a circle. The title text references the totality that occurs during a total solar eclipse and its corresponding shape (or "Venn diagram," as the title text phrases it).

This comic was released 8 days after the Solar eclipse of April 20, 2023, which was visible across parts of South East Asia and Australia, and of which an excited astronomer would certainly be aware.