When did Obi-Wan become Jedi Master and the Council member?

[Google]

Anakin achieved knighthood in "Clone Wars chapter 21". (Though Visual Dictionary indicates the novel "Jedi Trial" is the real canon.)

When did Obi-Wan become Jedi Master and the Council member? I can't remember any book tells this story.

[Vinceyoung]

There probably isn't much of a story behind it. A spot opens up, and then he gets picked.