we went to their Fifteith anniversary
is 50th capitalized?
No. And it's spelled like this ~~> fiftieth
Yes, "50th" is capitalized when referring to a specific event or anniversary. In the sentence you provided, since it is referring to their "Fiftieth anniversary," where "fiftieth" is an ordinal number, it should be capitalized as "Fiftieth." Capitalizing ordinal numbers, like "50th," emphasizes the significance of the anniversary.
To check for capitalization rules in general, you can refer to style guides such as The Chicago Manual of Style or The Associated Press Stylebook. These style guides provide guidelines for capitalization and other writing conventions commonly used in different fields. Additionally, you can also refer to dictionaries for specific capitalization rules of certain words or phrases.