Which of the following words fits the best in the blank?

Words: on/in/at

Phrase: “Chaos ____ the sky” is a noun phrase.

Yes, even this blog’s title has a 2/3 chance of being grammatically incorrect. (I went with “at” because the acronym is a common word.)

On a very unrelated note, apparently some people found this blog by searching “antiderivative of tangent“. Should I write some more posts that might be hit by a random googler?