Wikipedia:You do need to cite that the sky is blue

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Shortcuts WP:NOTBLUE WP:DOCITEBLUE WP:NOTBLUESKY WP:REDSKY

This page in a nutshell: Just because something appears obvious to you, doesn't mean it's obvious to everyone. Build articles from reliable, expert sources, and cite those sources.

It is sometimes felt that "obvious" statements, such as "the sky is blue", do not need citing. However, there are some reasons why you do need to cite the "obvious", such as that the sky is blue.

First of all, you do need citations in the "main" article, i.e., where the subject is the "obvious" statement or its major element. I.e., the statement "the sky is blue" must be footnoted in the article "Sky", especially in the section that discusses the color of the sky. Such references usually lead to more detailed knowledge.

Even the most obvious and simple assertion may need an explanation. The statement that the sky is blue needs explaining that it is due to Rayleigh scattering. Citing the sources that explain why it is blue would be valuable to some readers.

Readers come from different backgrounds and with different knowledges, cultures and experiences. It would be inappropriate to assume everyone's knowledge is the same.

Before making a statement, no matter how trivial or "obvious", make sure that it could not be misinterpreted or challenged.