21: Kepler

Explain xkcd: It's 'cause you're dumb.
Revision as of 18:10, 19 January 2013 by St.nerol (talk | contribs) (Explanation)
Jump to: navigation, search
Science joke. You should probably move along.
Title text: Science joke. You should probably move along.


Johannes Kepler was a German mathematician, astronomer and astrologer, best known for his laws of planetary motion. By observing our solar system each night at the same spot, Kepler was able to deduce that planets in the system do not move in a circular direction around the Sun, but rather in an elliptical way. According to Kepler's Second Law, "A line joining a planet and the Sun sweeps out equal areas during equal intervals of time."

In the comic, the janitor Kepler also sweeps the same area, although in this case "area" is used in the sense of "surface" (of floor) rather than in the purely mathematical sense.


  • [Original Randall quote]: "Another one which, if you don't get, you're probably better off."
  • This is the twentieth comic posted to livejournal. The previous was 20: Ferret. The next was 44: Love.


[Two people stand in an aisle in a store]
Person 1: Nice store. How do you keep the floors so clean?
Person 2: Oh, we hired this dude named Kepler, he's really good. Hard worker. Doesn't mind the monotony. Sweeps out the same area every night.

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


Rikthoff (talk) The date of issue of this comic is off. Does anybody have the correct issue date?

It appears to be accurate; it's the date from Randall's xkcd LiveJournal entry. Blaisepascal (talk) 02:21, 16 August 2012 (UTC)

Sorry, I fixed the date (to livejournal date) on August 8, 2012 but did not see/update talk page.--B. P. (talk) 18:39, 17 August 2012 (UTC)

I thought it was a reference to the Kepler telescope being pointed in the same direction for a long time, but I don't really know enough to be sure about that 02:14, 17 April 2015 (UTC)

It could be, Kepler was planned to be launched around the time this comic was originally published, but it was delayed due to budget cuts. While I think Kepler's Second Law explanation seems more relevant to the joke in the comic, I have updated the explanation and trivia sections to include Project Kepler. 18:40, 16 February 2017 (UTC)

There is a community portal discussion of what to call Cueball and what to do in case with more than one Cueball. I have added this comic to the new Category:Multiple Cueballs. Since the store manager Cueball has the interesting part of this comic, I have listed him as Cueball. Just made a note that the other guy also looks like Cueball.--Kynde (talk) 18:13, 16 March 2015 (UTC)

Need title text explanation. 23:38, 21 October 2017 (UTC)