Wiktionary
happen on
vb. to find by chance,
Usage examples of "happen on".
Not only did he at once recognize that a collision with the earth was possible, but he soon foresaw that it was inevitable, and that it must happen on the night of the 31st of December.
In private homes this could happen on trays placed on the rafters below the roof, but this frequent damping of the rafters wasn't good for the wood.
So far, that agenda had marched side-by-side with the Faith's, yet what would happen on the day that was no longer true?
People were so happy when it didn't happen on 2000 that they thought it never would.
Most everything that is to happen on a manned space flight is already known far in advance.