21: Kepler

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
Science joke. You should probably move along.
Title text: Science joke. You should probably move along.

[edit] Explanation

Johannes Kepler was a German mathematician, astronomer and astrologer, best known for his laws of planetary motion. By using Tycho Brahe's observations of our solar system, Brahe gave Kepler the job of observing and explaining the motion of the planet Mars, Kepler was able to deduce that planets in the system do not move in a circular orbit around the Sun, but rather in an elliptical one.

According to Kepler's Second Law, "A line joining a planet and the Sun sweeps out equal areas during equal intervals of time." This looks like wiping a wipe on the floor.

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.

[edit] Transcript

[Two people stand in an aisle in a store.]
Cueball 1: Nice store. How do you keep the floors so clean?
Cueball 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.

[edit] Trivia

  • 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.
comment.png add a comment! ⋅ 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)
Personal tools


It seems you are using noscript, which is stopping our project wonderful ads from working. Explain xkcd uses ads to pay for bandwidth, and we manually approve all our advertisers, and our ads are restricted to unobtrusive images and slow animated GIFs. If you found this site helpful, please consider whitelisting us.

Want to advertise with us, or donate to us with Paypal or Bitcoin?